ksh is a command interpreter that is intended for both interactive and
  shell script use. Its command language is a superset of the sh(1) shell
  language.
The following options can be specified only on the command line:
  - -c command-string
- the shell executes the command(s) contained in command-string
- -i
- interactive mode — see below
- -l
- login shell — see below interactive mode — see below
- -s
- the shell reads commands from standard input; all non-option arguments are
      positional parameters
- -r
- restricted mode — see below
In addition to the above, the options described in the set
    built-in command can also be used on the command line.
If neither the -c nor the -s options are specified,
    the first non-option argument specifies the name of a file the shell reads
    commands from; if there are no non-option arguments, the shell reads
    commands from standard input. The name of the shell (i.e., the
    contents of the $0) parameter is determined as follows: if the
    -c option is used and there is a non-option argument, it is used as
    the name; if commands are being read from a file, the file is used as the
    name; otherwise the name the shell was called with (i.e., argv[0]) is
    used.
A shell is interactive if the -i option is used or
    if both standard input and standard error are attached to a tty. An
    interactive shell has job control enabled (if available), ignores the INT,
    QUIT and TERM signals, and prints prompts before reading input (see
    PS1 and PS2 parameters). For non-interactive shells, the
    trackall option is on by default (see set command below).
A shell is restricted if the -r option is used or if
    either the basename of the name the shell is invoked with or the
    SHELL parameter match the pattern *r*sh (e.g., rsh, rksh,
    rpdksh, etc.). The following restrictions come into effect after the
    shell processes any profile and $ENV files:
  -   •
- the cd command is disabled
-   •
- the SHELL, ENV and PATH parameters can't be
    changed
-   •
- command names can't be specified with absolute or relative paths
-   •
- the -p option of the command built-in can't be used
-   •
- redirections that create files can't be used (i.e., >,
      >|, >>, <>)
A shell is privileged if the -p option is used or if
    the real user-id or group-id does not match the effective user-id or
    group-id (see getuid(2), getgid(2)). A privileged shell does
    not process $HOME/.profile nor the ENV parameter (see below), instead
    the file /etc/suid_profile is processed. Clearing the privileged option
    causes the shell to set its effective user-id (group-id) to its real user-id
    (group-id).
If the basename of the name the shell is called with (i.e.,
    argv[0]) starts with - or if the -l option is used, the shell
    is assumed to be a login shell and the shell reads and executes the contents
    of /etc/profile, $HOME/.profile and $ENV if they exist
    and are readable.
If the ENV parameter is set when the shell starts (or, in
    the case of login shells, after any profiles are processed), its value is
    subjected to parameter, command, arithmetic and tilde substitution and the
    resulting file (if any) is read and executed. If the ENV parameter is
    not set (and not null) the file $HOME/.kshrc is included (after the
    above mentioned substitutions have been performed).
The exit status of the shell is 127 if the command file specified
    on the command line could not be opened, or non-zero if a fatal syntax error
    occurred during the execution of a script. In the absence of fatal errors,
    the exit status is that of the last command executed, or zero, if no command
    is executed.
The shell begins parsing its input by breaking it into words. Words,
  which are sequences of characters, are delimited by unquoted
  white-space characters (space, tab and newline) or
  meta-characters (<, >, |, ;,
  &, ( and )). Aside from delimiting words, spaces and
  tabs are ignored, while newlines usually delimit commands. The meta-characters
  are used in building the following tokens: <, <&,
  <<, >, >&, >>, etc.
  are used to specify redirections (see Input/Output Redirection below);
  | is used to create pipelines; |& is used to create
  co-processes (see Co-Processes below); ; is used to separate commands;
  & is used to create asynchronous pipelines; && and
  || are used to specify conditional execution; ;; is used in
  case statements; (( .. )) are used in arithmetic
  expressions; and lastly, ( .. ) are used to create subshells.
White-space and meta-characters can be quoted individually using
    backslash (\), or in groups using double (") or single
    (') quotes. Note that the following characters are also treated
    specially by the shell and must be quoted if they are to represent
    themselves: \, ", ', #, $, `,
    ~, {, }, *, ? and [. The first
    three of these are the above mentioned quoting characters (see Quoting
    below); #, if used at the beginning of a word, introduces a comment
    — everything after the # up to the nearest newline is ignored;
    $ is used to introduce parameter, command and arithmetic
    substitutions (see Substitution below); ` introduces an old-style
    command substitution (see Substitution below); ~ begins a directory
    expansion (see Tilde Expansion below); { and } delimit
    csh(1) style alternations (see Brace Expansion below); and, finally,
    *, ? and [ are used in file name generation (see File
    Name Patterns below).
As words and tokens are parsed, the shell builds commands, of
    which there are two basic types: simple-commands, typically programs
    that are executed, and compound-commands, such as for and
    if statements, grouping constructs and function definitions.
A simple-command consists of some combination of parameter
    assignments (see Parameters below), input/output redirections (see
    Input/Output Redirections below), and command words; the only restriction is
    that parameter assignments come before any command words. The command words,
    if any, define the command that is to be executed and its arguments. The
    command may be a shell built-in command, a function or an external
    command, i.e., a separate executable file that is located
    using the PATH parameter (see Command Execution below). Note that all
    command constructs have an exit status: for external commands, this
    is related to the status returned by wait(2) (if the command could
    not be found, the exit status is 127, if it could not be executed, the exit
    status is 126); the exit status of other command constructs (built-in
    commands, functions, compound-commands, pipelines, lists, etc.) are
    all well defined and are described where the construct is described. The
    exit status of a command consisting only of parameter assignments is that of
    the last command substitution performed during the parameter assignment or
    zero if there were no command substitutions.
Commands can be chained together using the | token to form
    pipelines, in which the standard output of each command but the last
    is piped (see pipe(2)) to the standard input of the following
    command. The exit status of a pipeline is that of its last command. A
    pipeline may be prefixed by the ! reserved word which causes the exit
    status of the pipeline to be logically complemented: if the original status
    was 0 the complemented status will be 1, and if the original status was not
    0, then the complemented status will be 0.
Lists of commands can be created by separating pipelines by
    any of the following tokens: &&, ||, &,
    |& and ;. The first two are for conditional execution:
    cmd1 && cmd2 executes cmd2 only if the
    exit status of cmd1 is zero; || is the opposite —
    cmd2 is executed only if the exit status of cmd1 is non-zero.
    && and || have equal precedence which is higher than
    that of &, |& and ;, which also have equal
    precedence. The & token causes the preceding command to be
    executed asynchronously, that is, the shell starts the command, but does not
    wait for it to complete (the shell does keep track of the status of
    asynchronous commands — see Job Control below). When an asynchronous
    command is started when job control is disabled (i.e., in most
    scripts), the command is started with signals INT and QUIT ignored and with
    input redirected from /dev/null (however, redirections specified in the
    asynchronous command have precedence). The |& operator starts a
    co-process which is special kind of asynchronous process (see
    Co-Processes below). Note that a command must follow the &&
    and || operators, while a command need not follow &,
    |& and ;. The exit status of a list is that of the last
    command executed, with the exception of asynchronous lists, for which the
    exit status is 0.
Compound commands are created using the following reserved words
    — these words are only recognized if they are unquoted and if they
    are used as the first word of a command (i.e., they can't be preceded
    by parameter assignments or redirections):
  
    | case | else | function | then | ! | 
  
    | do | esac | if | time | [[ | 
  
    | done | fi | in | until | { | 
  
    | elif | for | select | while | } | 
Note: Some shells (but not this one) execute control structure commands
  in a subshell when one or more of their file descriptors are redirected, so
  any environment changes inside them may fail. To be portable, the exec
  statement should be used instead to redirect file descriptors before the
  control structure.
In the following compound command descriptions, command lists
    (denoted as list) that are followed by reserved words must end with a
    semi-colon, a newline or a (syntactically correct) reserved word. For
    example,
{ echo foo; echo bar; }
{ echo foo; echo bar<newline>}
{ { echo foo; echo bar; } }
are all valid, but
{ echo foo; echo bar }
is not.
  - ( list )
- Execute list in a subshell. There is no implicit way to pass
      environment changes from a subshell back to its parent.
- { list }
- Compound construct; list is executed, but not in a subshell. Note
      that { and } are reserved words, not meta-characters.
- case word in [ [(] pattern [|
    pattern] ... ) list ;; ] ... esac
- The case statement attempts to match word against the
      specified patterns; the list associated with the first
      successfully matched pattern is executed. Patterns used in case
      statements are the same as those used for file name patterns except that
      the restrictions regarding . and / are dropped. Note that
      any unquoted space before and after a pattern is stripped; any space with
      a pattern must be quoted. Both the word and the patterns are subject to
      parameter, command, and arithmetic substitution as well as tilde
      substitution. For historical reasons, open and close braces may be used
      instead of in and esac (e.g., case $foo { *) echo
      bar; }). The exit status of a case statement is that of the
      executed list; if no list is executed, the exit status is
      zero.
- for name [ in word ... term ] do
    list done
- where term is either a newline or a ;. For each word
      in the specified word list, the parameter name is set to the word
      and list is executed. If in is not used to specify a word
      list, the positional parameters ("$1",
      "$2", etc.) are used instead. For historical
      reasons, open and close braces may be used instead of do and
      done (e.g., for i; { echo $i; }). The exit status of
      a for statement is the last exit status of list; if
      list is never executed, the exit status is zero.
- if list then list [elif list
    then list] ... [else list] fi
- If the exit status of the first list is zero, the second
      list is executed; otherwise the list following the
      elif, if any, is executed with similar consequences. If all the
      lists following the if and elifs fail (i.e., exit
      with non-zero status), the list following the else is
      executed. The exit status of an if statement is that of
      non-conditional list that is executed; if no non-conditional
      list is executed, the exit status is zero.
- select name [ in word ... term ]
    do list done
- where term is either a newline or a ;. The select
      statement provides an automatic method of presenting the user with a menu
      and selecting from it. An enumerated list of the specified words is
      printed on standard error, followed by a prompt (PS3, normally
      `#? '). A number corresponding to one of the enumerated words is
      then read from standard input, name is set to the selected word (or
      is unset if the selection is not valid), REPLY is set to what was
      read (leading/trailing space is stripped), and list is executed. If
      a blank line (i.e., zero or more IFS characters) is entered,
      the menu is re-printed without executing list. When list
      completes, the enumerated list is printed if REPLY is null, the
      prompt is printed and so on. This process is continues until an
      end-of-file is read, an interrupt is received or a break statement is
      executed inside the loop. If in word ... is omitted,
      the positional parameters are used (i.e., "$1",
      "$2", etc.). For historical reasons, open and
      close braces may be used instead of do and done
      (e.g., select i; { echo $i; }). The exit status of a
      select statement is zero if a break statement is used to exit the
      loop, non-zero otherwise.
- until list do list done
- This works like while, except that the body is executed only while
      the exit status of the first list is non-zero.
- while list do list done
- A while is a prechecked loop. Its body is executed as often as the
      exit status of the first list is zero. The exit status of a
      while statement is the last exit status of the list in the
      body of the loop; if the body is not executed, the exit status is
    zero.
- function name { list }
- Defines the function name. See Functions below. Note that
      redirections specified after a function definition are performed whenever
      the function is executed, not when the function definition is
    executed.
- name () command
- Mostly the same as function. See Functions below.
- time [ -p ] [ pipeline ]
- The time reserved word is described in the Command Execution
      section.
- (( expression ))
- The arithmetic expression expression is evaluated; equivalent to
      let "expression". See Arithmetic
      Expressions and the let command below.
- [[ expression ]]
- Similar to the test and [ ... ] commands (described
      later), with the following exceptions:
  -   •
- Field splitting and file name generation are not performed on
    arguments.
-   •
- The -a (and) and -o (or) operators are replaced with
      && and ||, respectively.
-   •
- Operators (e.g., -f, =, !, etc.) must
      be unquoted.
-   •
- The second operand of != and = expressions are patterns
      (e.g., the comparison in
    
 [[ foobar = f*r ]]
 succeeds).
-   •
- There are two additional binary operators: < and >
      which return true if their first string operand is less than, or greater
      than, their second string operand, respectively.
-   •
- The single argument form of test, which tests if the argument has
      non-zero length, is not valid - explicit operators must always be used,
      e.g., instead of
    
 [ str ]
 use
 [[ -n str ]]
 
-   •
- Parameter, command and arithmetic substitutions are performed as
      expressions are evaluated and lazy expression evaluation is used for the
      && and || operators. This means that in the
      statement
    
 [[ -r foo && $(< foo) = b*r ]]
 the $(< foo) is evaluated if and only if the file foo
      exists and is readable.
 
Quoting is used to prevent the shell from treating characters or words
  specially. There are three methods of quoting: First, \ quotes the
  following character, unless it is at the end of a line, in which case both the
  \ and the newline are stripped. Second, a single quote (')
  quotes everything up to the next single quote (this may span lines). Third, a
  double quote (") quotes all characters, except $, `
  and \, up to the next unquoted double quote. $ and `
  inside double quotes have their usual meaning (i.e., parameter, command
  or arithmetic substitution) except no field splitting is carried out on the
  results of double-quoted substitutions. If a \ inside a double-quoted
  string is followed by \, $, ` or ", it is
  replaced by the second character; if it is followed by a newline, both the
  \ and the newline are stripped; otherwise, both the \ and the
  character following are unchanged.
Note: An earlier version of ksh(1) changed the interpretation of
    sequences of the form
    "...`...\"...`.."
    according to whether or not POSIX mode was in effect. In the current
    implementation, the backslash in \" is seen and removed by the
    outer "...", so the backslash is not seen by the
    inner `...`.
There are two types of aliases: normal command aliases and tracked aliases.
  Command aliases are normally used as a short hand for a long or often used
  command. The shell expands command aliases (i.e., substitutes the alias
  name for its value) when it reads the first word of a command. An expanded
  alias is re-processed to check for more aliases. If a command alias ends in a
  space or tab, the following word is also checked for alias expansion. The
  alias expansion process stops when a word that is not an alias is found, when
  a quoted word is found or when an alias word that is currently being expanded
  is found.
The following command aliases are defined automatically by the
    shell: 
autoload='typeset -fu'
functions='typeset -f'
hash='alias -t'
history='fc -l'
integer='typeset -i'
local='typeset'
login='exec login'
nohup='nohup '
r='fc -e -'
stop='kill -STOP'
suspend='kill -STOP $$'
type='whence -v'
Tracked aliases allow the shell to remember where it found a
    particular command. The first time the shell does a path search for a
    command that is marked as a tracked alias, it saves the full path of the
    command. The next time the command is executed, the shell checks the saved
    path to see that it is still valid, and if so, avoids repeating the path
    search. Tracked aliases can be listed and created using alias -t.
    Note that changing the PATH parameter clears the saved paths for all
    tracked aliases. If the trackall option is set (i.e., set
    -o trackall or set -h), the shell tracks all commands. This
    option is set automatically for non-interactive shells. For interactive
    shells, only the following commands are automatically tracked: cat,
    cc, chmod, cp, date, ed, emacs,
    grep, ls, mail, make, mv, pr,
    rm, sed, sh, vi and who.
The first step the shell takes in executing a simple-command is to perform
  substitutions on the words of the command. There are three kinds of
  substitution: parameter, command and arithmetic. Parameter substitutions,
  which are described in detail in the next section, take the form $name
  or ${...}; command substitutions take the form
  $(command) or `command`; and
  arithmetic substitutions take the form $((expression)).
If a substitution appears outside of double quotes, the results of
    the substitution are generally subject to word or field splitting according
    to the current value of the IFS parameter. The IFS parameter
    specifies a list of characters which are used to break a string up into
    several words; any characters from the set space, tab and newline that
    appear in the IFS characters are called IFS white space. Sequences of
    one or more IFS white space characters, in combination with zero or one
    non-IFS white space characters delimit a field. As a special case, leading
    and trailing IFS white space is stripped (i.e., no leading or
    trailing empty field is created by it); leading or trailing non-IFS white
    space does create an empty field. Example: if IFS is set to
    `<space>:', the sequence of characters
    `<space>A<space>:<space><space>B::D' contains four
    fields: `A', `B', `' and `D'. Note that if the IFS parameter is set
    to the null string, no field splitting is done; if the parameter is unset,
    the default value of space, tab and newline is used.
The results of substitution are, unless otherwise specified, also
    subject to brace expansion and file name expansion (see the relevant
    sections below).
A command substitution is replaced by the output generated by the
    specified command, which is run in a subshell. For
    $(command) substitutions, normal quoting rules are used
    when command is parsed, however, for the
    `command` form, a \ followed by any of $,
    ` or \ is stripped (a \ followed by any other character
    is unchanged). As a special case in command substitutions, a command of the
    form < file is interpreted to mean substitute the contents
    of file ($(< foo) has the same effect as $(cat foo), but it is
    carried out more efficiently because no process is started).
  
  NOTE: $(command) expressions are currently parsed by
    finding the matching parenthesis, regardless of quoting. This will hopefully
    be fixed soon.
Arithmetic substitutions are replaced by the value of the
    specified expression. For example, the command echo $((2+3*4)) prints
    14. See Arithmetic Expressions for a description of an
  expression.
Parameters are shell variables; they can be assigned values and their values can
  be accessed using a parameter substitution. A parameter name is either one of
  the special single punctuation or digit character parameters described below,
  or a letter followed by zero or more letters or digits (`_' counts as a
  letter). The later form can be treated as arrays by appending an array index
  of the form: [expr] where expr is an arithmetic
  expression. Array indices are currently limited to the range 0 through 1023,
  inclusive. Parameter substitutions take the form $name,
  ${name} or
  ${name[expr]}, where name is a
  parameter name. If substitution is performed on a parameter (or an array
  parameter element) that is not set, a null string is substituted unless the
  nounset option (set -o nounset or set -u) is set, in
  which case an error occurs.
Parameters can be assigned values in a number of ways. First, the
    shell implicitly sets some parameters like #, PWD, etc.; this
    is the only way the special single character parameters are set. Second,
    parameters are imported from the shell's environment at startup. Third,
    parameters can be assigned values on the command line, for example,
    `FOO=bar' sets the parameter FOO to bar; multiple parameter
    assignments can be given on a single command line and they can be followed
    by a simple-command, in which case the assignments are in effect only for
    the duration of the command (such assignments are also exported, see below
    for implications of this). Note that both the parameter name and the
    = must be unquoted for the shell to recognize a parameter assignment.
    The fourth way of setting a parameter is with the export,
    readonly and typeset commands; see their descriptions in the
    Command Execution section. Fifth, for and select loops set
    parameters as well as the getopts, read and set -A
    commands. Lastly, parameters can be assigned values using assignment
    operators inside arithmetic expressions (see Arithmetic Expressions below)
    or using the ${name=value} form of
    parameter substitution (see below).
Parameters with the export attribute (set using the export
    or typeset -x commands, or by parameter assignments followed by
    simple commands) are put in the environment (see environ(7)) of
    commands run by the shell as name=value pairs. The
    order in which parameters appear in the environment of a command is
    unspecified. When the shell starts up, it extracts parameters and their
    values from its environment and automatically sets the export attribute for
    those parameters.
Modifiers can be applied to the ${name} form
    of parameter substitution:
  - ${name:-word}
- if name is set and not null, it is substituted, otherwise
      word is substituted.
- ${name:+word}
- if name is set and not null, word is substituted, otherwise
      nothing is substituted.
- ${name:=word}
- if name is set and not null, it is substituted, otherwise it is
      assigned word and the resulting value of name is
      substituted.
- ${name:?word}
- if name is set and not null, it is substituted, otherwise
      word is printed on standard error (preceded by name:) and an
      error occurs (normally causing termination of a shell script, function or
      .-script). If word is omitted the string `parameter null or not set' is
      used instead.
In the above modifiers, the : can be omitted, in which case
    the conditions only depend on name being set (as opposed to set and
    not null). If word is needed, parameter, command, arithmetic and
    tilde substitution are performed on it; if word is not needed, it is
    not evaluated.
The following forms of parameter substitution can also be
  used:
  - ${#name}
- The number of positional parameters if name is *, @
      or is not specified, or the length of the string value of parameter
      name.
- ${#name[*]}, ${#name[@]}
- The number of elements in the array name.
- ${name#pattern},
    ${name##pattern}
- If pattern matches the beginning of the value of parameter
      name, the matched text is deleted from the result of substitution.
      A single # results in the shortest match, two #'s results in
      the longest match.
- ${name%pattern},
    ${name%%pattern}
- Like ${..#..} substitution, but it deletes from the
      end of the value.
The following special parameters are implicitly set by the shell
    and cannot be set directly using assignments:
  - !
- Process id of the last background process started. If no background
      processes have been started, the parameter is not set.
- #
- The number of positional parameters (i.e., $1, $2,
      etc.).
- $
- The process ID of the shell, or the PID of the original shell if it is a
      subshell.
- -
- The concatenation of the current single letter options (see set
      command below for list of options).
- ?
- The exit status of the last non-asynchronous command executed. If the last
      command was killed by a signal, $? is set to 128 plus the signal
      number.
- 0
- The name the shell was invoked with (i.e., argv[0]), or the
      command-name if it was invoked with the -c option and the
      command-name was supplied, or the file argument, if it was
      supplied. If the posix option is not set, $0 is the name of
      the current function or script.
- 1 ... 9
- The first nine positional parameters that were supplied to the shell,
      function or .-script. Further positional parameters may be accessed
      using ${number}.
- *
- All positional parameters (except parameter 0), i.e., $1 $2
      $3.... If used outside of double quotes, parameters are separate words
      (which are subjected to word splitting); if used within double quotes,
      parameters are separated by the first character of the IFS
      parameter (or the empty string if IFS is null).
- @
- Same as $*, unless it is used inside double quotes, in which case a
      separate word is generated for each positional parameter - if there are no
      positional parameters, no word is generated ("$@" can be used to
      access arguments, verbatim, without losing null arguments or splitting
      arguments with spaces).
The following parameters are set and/or used by the shell:
  - _ (underscore)
- When an external command is executed by the shell, this parameter is set
      in the environment of the new process to the path of the executed command.
      In interactive use, this parameter is also set in the parent shell to the
      last word of the previous command. When MAILPATH messages are
      evaluated, this parameter contains the name of the file that changed (see
      MAILPATH parameter below).
- CDPATH
- Search path for the cd built-in command. Works the same way as
      PATH for those directories not beginning with / in cd
      commands. Note that if CDPATH is set and does not contain . nor an
      empty path, the current directory is not searched.
- COLUMNS
- Set to the number of columns on the terminal or window. Currently set to
      the cols value as reported by stty(1) if that value is
      non-zero. This parameter is used by the interactive line editing modes,
      and by select, set -o and kill -l commands to format
      information in columns.
- EDITOR
- If the VISUAL parameter is not set, this parameter controls the
      command line editing mode for interactive shells. See VISUAL
      parameter below for how this works.
- ENV
- If this parameter is found to be set after any profile files are executed,
      the expanded value is used as a shell start-up file. It typically contains
      function and alias definitions.
- ERRNO
- Integer value of the shell's errno variable — indicates the reason
      the last system call failed.
    Not implemented yet. 
- EXECSHELL
- If set, this parameter is assumed to contain the shell that is to be used
      to execute commands that execve(2) fails to execute and which do
      not start with a `#! shell' sequence.
- FCEDIT
- The editor used by the fc command (see below).
- FPATH
- Like PATH, but used when an undefined function is executed to
      locate the file defining the function. It is also searched when a command
      can't be found using PATH. See Functions below for more
      information.
- HISTFILE
- The name of the file used to store history. When assigned to, history is
      loaded from the specified file. Also, several invocations of the shell
      running on the same machine will share history if their HISTFILE
      parameters all point at the same file.
    
 NOTE: if HISTFILE isn't set, no history file is used. This is different from
      the original Korn shell, which uses $HOME/.sh_history; in future,
      pdksh may also use a default history file.
- HISTSIZE
- The number of commands normally stored for history, default 128.
- HOME
- The default directory for the cd command and the value substituted
      for an unqualified ~ (see Tilde Expansion below).
- IFS
- Internal field separator, used during substitution and by the read
      command, to split values into distinct arguments; normally set to space,
      tab and newline. See Substitution above for details.
    
 Note: this parameter is not imported from the environment when the
      shell is started.
- KSH_VERSION
- The version of shell and the date the version was created (readonly). See
      also the version commands in Emacs Editing Mode and Vi Editing Mode
      sections, below.
- LINENO
- The line number of the function or shell script that is currently being
      executed.
- LINES
- Set to the number of lines on the terminal or window.
    Not implemented yet. 
- MAIL
- If set, the user will be informed of the arrival of mail in the named
      file. This parameter is ignored if the MAILPATH parameter is
    set.
- MAILCHECK
- How often, in seconds, the shell will check for mail in the file(s)
      specified by MAIL or MAILPATH. If 0, the shell checks before
      each prompt. The default is 600 (10 minutes).
- MAILPATH
- A list of files to be checked for mail. The list is colon separated, and
      each file may be followed by a ? and a message to be printed if new
      mail has arrived. Command, parameter and arithmetic substitution is
      performed on the message, and, during substitution, the parameter
      $_ contains the name of the file. The default message is you
      have mail in $_.
- OLDPWD
- The previous working directory. Unset if cd has not successfully
      changed directories since the shell started, or if the shell doesn't know
      where it is.
- OPTARG
- When using getopts, it contains the argument for a parsed option,
      if it requires one.
- OPTIND
- The index of the last argument processed when using getopts.
      Assigning 1 to this parameter causes getopts to process arguments
      from the beginning the next time it is invoked.
- PATH
- A colon separated list of directories that are searched when looking for
      commands and .'d files. An empty string resulting from a leading or
      trailing colon, or two adjacent colons is treated as a `.', the current
      directory.
- POSIXLY_CORRECT
- If set, this parameter causes the posix option to be enabled. See
      POSIX Mode below.
- PPID
- The process ID of the shell's parent (readonly).
- PS1
- PS1 is the primary prompt for interactive shells. Parameter,
      command and arithmetic substitutions are performed, and ! is
      replaced with the current command number (see fc command below). A
      literal ! can be put in the prompt by placing !! in PS1. Note that since
      the command line editors try to figure out how long the prompt is (so they
      know how far it is to edge of the screen), escape codes in the prompt tend
      to mess things up. You can tell the shell not to count certain sequences
      (such as escape codes) by prefixing your prompt with a non-printing
      character (such as control-A) followed by a carriage return and then
      delimiting the escape codes with this non-printing character. If you don't
      have any non-printing characters, you're out of luck... BTW, don't blame
      me for this hack; it's in the original ksh. Default is `$ '
      for non-root users, `# ' for root.
- PS2
- Secondary prompt string, by default `> ', used when more input
      is needed to complete a command.
- PS3
- Prompt used by select statement when reading a menu selection.
      Default is `#? '.
- PS4
- Used to prefix commands that are printed during execution tracing (see
      set -x command below). Parameter, command and arithmetic
      substitutions are performed before it is printed. Default is
      `+ '.
- PWD
- The current working directory. Maybe unset or null if shell doesn't know
      where it is.
- RANDOM
- A simple random number generator. Every time RANDOM is referenced,
      it is assigned the next number in a random number series. The point in the
      series can be set by assigning a number to RANDOM (see
      rand(3)).
- REPLY
- Default parameter for the read command if no names are given. Also
      used in select loops to store the value that is read from standard
      input.
- SECONDS
- The number of seconds since the shell started or, if the parameter has
      been assigned an integer value, the number of seconds since the assignment
      plus the value that was assigned.
- TMOUT
- If set to a positive integer in an interactive shell, it specifies the
      maximum number of seconds the shell will wait for input after printing the
      primary prompt (PS1). If the time is exceeded, the shell
    exits.
- TMPDIR
- The directory shell temporary files are created in. If this parameter is
      not set, or does not contain the absolute path of a writable directory,
      temporary files are created in /tmp.
- VISUAL
- If set, this parameter controls the command line editing mode for
      interactive shells. If the last component of the path specified in this
      parameter contains the string vi, emacs or gmacs, the
      vi, emacs or gmacs (Gosling emacs) editing mode is enabled,
    respectively.
Tilde expansion, which is done in parallel with parameter substitution, is done
  on words starting with an unquoted ~. The characters following the
  tilde, up to the first /, if any, are assumed to be a login name. If
  the login name is empty, + or -, the value of the HOME,
  PWD, or OLDPWD parameter is substituted, respectively.
  Otherwise, the password file is searched for the login name, and the tilde
  expression is substituted with the user's home directory. If the login name is
  not found in the password file or if any quoting or parameter substitution
  occurs in the login name, no substitution is performed.In parameter assignments (those preceding a simple-command or
    those occurring in the arguments of alias, export,
    readonly, and typeset), tilde expansion is done after any
    unquoted colon (:), and login names are also delimited by colons.
The home directory of previously expanded login names are cached
    and re-used. The alias -d command may be used to list, change and add
    to this cache (e.g., `alias -d fac=/usr/local/facilities; cd
    ~fac/bin').
Brace expressions, which take the form
prefix{str1,...,strN}suffix
are expanded to N words, each of which is the concatenation of prefix,
  stri and suffix (e.g., `a{c,b{X,Y},d}e' expands to four
  word: ace, abXe, abYe, and ade). As noted in the example, brace expressions
  can be nested and the resulting words are not sorted. Brace expressions must
  contain an unquoted comma (,) for expansion to occur (i.e.,
  {} and {foo} are not expanded). Brace expansion is carried out
  after parameter substitution and before file name generation.
A file name pattern is a word containing one or more unquoted ? or
  * characters or [..] sequences. Once brace expansion has
  been performed, the shell replaces file name patterns with the sorted names of
  all the files that match the pattern (if no files match, the word is left
  unchanged). The pattern elements have the following meaning:
  - ?
- matches any single character.
- *
- matches any sequence of characters.
- [..]
- matches any of the characters inside the brackets. Ranges of characters
      can be specified by separating two characters by a -, e.g.,
      [a0-9] matches the letter a or any digit. In order to
      represent itself, a - must either be quoted or the first or last
      character in the character list. Similarly, a ] must be quoted or
      the first character in the list if it is represent itself instead of the
      end of the list. Also, a ! appearing at the start of the list has
      special meaning (see below), so to represent itself it must be quoted or
      appear later in the list.
- [!..]
- like [..], except it matches any character not inside the
      brackets.
- *(pattern| ... |pattern)
- matches any string of characters that matches zero or more occurrences of
      the specified patterns. Example: the pattern *(foo|bar) matches the
      strings `', `foo', `bar', `foobarfoo', etc..
- +(pattern| ... |pattern)
- matches any string of characters that matches one or more occurrences of
      the specified patterns. Example: the pattern +(foo|bar) matches the
      strings `foo', `bar', `foobarfoo', etc..
- ?(pattern| ... |pattern)
- matches the empty string or a string that matches one of the specified
      patterns. Example: the pattern ?(foo|bar) only matches the strings
      `', `foo' and `bar'.
- @(pattern| ... |pattern)
- matches a string that matches one of the specified patterns. Example: the
      pattern @(foo|bar) only matches the strings `foo' and `bar'.
- !(pattern| ... |pattern)
- matches any string that does not match one of the specified patterns.
      Examples: the pattern !(foo|bar) matches all strings except `foo'
      and `bar'; the pattern !(*) matches no strings; the pattern
      !(?)* matches all strings (think about it).
Note that pdksh currently never matches . and ..,
    but the original ksh, Bourne sh and bash do, so this may have to change (too
    bad).
Note that none of the above pattern elements match either a period
    (.) at the start of a file name or a slash (/), even if they
    are explicitly used in a [..] sequence; also, the names
    . and .. are never matched, even by the pattern .*.
If the markdirs option is set, any directories that result
    from file name generation are marked with a trailing /.
The POSIX character classes (i.e.,
    [:class-name:] inside a [..] expression)
    are not yet implemented.
When a command is executed, its standard input, standard output and standard
  error (file descriptors 0, 1 and 2, respectively) are normally inherited from
  the shell. Three exceptions to this are commands in pipelines, for which
  standard input and/or standard output are those set up by the pipeline,
  asynchronous commands created when job control is disabled, for which standard
  input is initially set to be from /dev/null, and commands for which any
  of the following redirections have been specified:
  - > file
- standard output is redirected to file. If file does not
      exist, it is created; if it does exist, is a regular file and the
      noclobber option is set, an error occurs, otherwise the file is
      truncated. Note that this means the command cmd < foo > foo
      will open foo for reading and then truncate it when it opens it for
      writing, before cmd gets a chance to actually read foo.
- >| file
- same as >, except the file is truncated, even if the
      noclobber option is set.
- >> file
- same as >, except the file an existing file is appended to
      instead of being truncated. Also, the file is opened in append mode, so
      writes always go to the end of the file (see open(2)).
- < file
- standard input is redirected from file, which is opened for
      reading.
- <> file
- same as <, except the file is opened for reading and
    writing.
- << marker
- after reading the command line containing this kind of redirection (called
      a here document), the shell copies lines from the command source into a
      temporary file until a line matching marker is read. When the
      command is executed, standard input is redirected from the temporary file.
      If marker contains no quoted characters, the contents of the
      temporary file are processed as if enclosed in double quotes each time the
      command is executed, so parameter, command and arithmetic substitutions
      are performed, along with backslash (\) escapes for $,
      `, \ and \newline. If multiple here documents are
      used on the same command line, they are saved in order.
- <<- marker
- same as <<, except leading tabs are stripped from lines in
      the here document.
- <& fd
- standard input is duplicated from file descriptor fd. fd can
      be a single digit, indicating the number of an existing file descriptor,
      the letter p, indicating the file descriptor associated with the
      output of the current co-process, or the character -, indicating
      standard input is to be closed.
- >& fd
- same as <&, except the operation is done on standard
    output.
In any of the above redirections, the file descriptor that is
    redirected (i.e., standard input or standard output) can be
    explicitly given by preceding the redirection with a single digit.
    Parameter, command and arithmetic substitutions, tilde substitutions and (if
    the shell is interactive) file name generation are all performed on the
    file, marker and fd arguments of redirections. Note
    however, that the results of any file name generation are only used if a
    single file is matched; if multiple files match, the word with the
    unexpanded file name generation characters is used. Note that in restricted
    shells, redirections which can create files cannot be used.
For simple-commands, redirections may appear anywhere in the
    command, for compound-commands (if statements, etc.), any
    redirections must appear at the end. Redirections are processed after
    pipelines are created and in the order they are given, so
cat /foo/bar 2>&1 > /dev/null | cat
  -n
will print an error with a line number prepended to it.
Integer arithmetic expressions can be used with the let command, inside
  $((..)) expressions, inside array references (e.g.,
  name[expr]), as numeric arguments to the
  test command, and as the value of an assignment to an integer
  parameter.
Expression may contain alpha-numeric parameter identifiers, array
    references, and integer constants and may be combined with the following C
    operators (listed and grouped in increasing order of precedence).
  - Unary operators:
- + - ! ~ ++ --
- Binary operators:
- ,
    
 = *= /= %= += -= <<= >>= &= ^= |=
 ||
 &&
 |
 ^
 &
 == !=
 < <= >= >
 << >>
 + -
 * / %
- Ternary operator:
- ?: (precedence is immediately higher than assignment)
- Grouping operators:
- ( )
Integer constants may be specified with arbitrary bases using the
    notation base#number, where base is a decimal
    integer specifying the base, and number is a number in the specified
    base.
The operators are evaluated as follows:
  - unary +
- result is the argument (included for completeness).
- unary -
- negation.
- !
- logical not; the result is 1 if argument is zero, 0 if not.
- ~
- arithmetic (bit-wise) not.
- ++
- increment; must be applied to a parameter (not a literal or other
      expression) - the parameter is incremented by 1. When used as a prefix
      operator, the result is the incremented value of the parameter, when used
      as a postfix operator, the result is the original value of the
    parameter.
- --
- similar to ++, except the parameter is decremented by 1.
- ,
- separates two arithmetic expressions; the left hand side is evaluated
      first, then the right. The result is value of the expression on the right
      hand side.
- =
- assignment; variable on the left is set to the value on the right.
- *= /= %= += -= <<= >>= &= ^= |=
- assignment operators; <var> <op>=
      <expr> is the same as <var> =
      <var> <op> ( <expr> ).
- ||
- logical or; the result is 1 if either argument is non-zero, 0 if not. The
      right argument is evaluated only if the left argument is zero.
- &&
- logical and; the result is 1 if both arguments are non-zero, 0 if not. The
      right argument is evaluated only if the left argument is non-zero.
- |
- arithmetic (bit-wise) or.
- ^
- arithmetic (bit-wise) exclusive-or.
- &
- arithmetic (bit-wise) and.
- ==
- equal; the result is 1 if both arguments are equal, 0 if not.
- !=
- not equal; the result is 0 if both arguments are equal, 1 if not.
- <
- less than; the result is 1 if the left argument is less than the right, 0
      if not.
- <= >= >
- less than or equal, greater than or equal, greater than. See <.
- << >>
- shift left (right); the result is the left argument with its bits shifted
      left (right) by the amount given in the right argument.
- + - * /
- addition, subtraction, multiplication, and division.
- %
- remainder; the result is the remainder of the division of the left
      argument by the right. The sign of the result is unspecified if either
      argument is negative.
- <arg1> ? <arg2> :
    <arg3>
- if <arg1> is non-zero, the result is <arg2>,
      otherwise <arg3>.
 
A co-process, which is a pipeline created with the |& operator, is an
  asynchronous process that the shell can both write to (using print -p)
  and read from (using read -p). The input and output of the co-process
  can also be manipulated using >&p and <&p
  redirections, respectively. Once a co-process has been started, another can't
  be started until the co-process exits, or until the co-process input has been
  redirected using an exec n>&p redirection. If a
  co-process's input is redirected in this way, the next co-process to be
  started will share the output with the first co-process, unless the output of
  the initial co-process has been redirected using an exec
  n<&p redirection.
Some notes concerning co-processes:
  -   •
- the only way to close the co-process input (so the co-process reads an
      end-of-file) is to redirect the input to a numbered file descriptor and
      then close that file descriptor (e.g., exec 3>&p;exec
      3>&-).
-   •
- in order for co-processes to share a common output, the shell must keep
      the write portion of the output pipe open. This means that end of file
      will not be detected until all co-processes sharing the co-process output
      have exited (when they all exit, the shell closes its copy of the pipe).
      This can be avoided by redirecting the output to a numbered file
      descriptor (as this also causes the shell to close its copy). Note that
      this behaviour is slightly different from the original Korn shell which
      closes its copy of the write portion of the co-processes' output when the
      most recently started co-process (instead of when all sharing
      co-processes) exits.
-   •
- print -p will ignore SIGPIPE signals during writes if the signal is
      not being trapped or ignored; the same is not true if the co-process input
      has been duplicated to another file descriptor and print -un
      is used.
Functions are defined using either Korn shell function name syntax
  or the Bourne/POSIX shell name() syntax (see below for the
  difference between the two forms). Functions are like .-scripts in that
  they are executed in the current environment, however, unlike
  .-scripts, shell arguments (i.e., positional parameters,
  $1, etc.) are never visible inside them. When the shell is
  determining the location of a command, functions are searched after special
  built-in commands, and before regular and non-regular built-ins, and before
  the PATH is searched.An existing function may be deleted using unset -f
    function-name. A list of functions can be obtained using typeset
    +f and the function definitions can be listed using typeset -f.
    autoload (which is an alias for typeset -fu) may be used to
    create undefined functions; when an undefined function is executed, the
    shell searches the path specified in the FPATH parameter for a file
    with the same name as the function, which, if found is read and executed. If
    after executing the file, the named function is found to be defined, the
    function is executed, otherwise, the normal command search is continued
    (i.e., the shell searches the regular built-in command table and
    PATH). Note that if a command is not found using PATH, an
    attempt is made to autoload a function using FPATH (this is an
    undocumented feature of the original Korn shell).
Functions can have two attributes, trace and export, which can be
    set with typeset -ft and typeset -fx, respectively. When a
    traced function is executed, the shell's xtrace option is turned on
    for the functions duration, otherwise the xtrace option is turned
    off. The export attribute of functions is currently not used. In the
    original Korn shell, exported functions are visible to shell scripts that
    are executed.
Since functions are executed in the current shell environment,
    parameter assignments made inside functions are visible after the function
    completes. If this is not the desired effect, the typeset command can
    be used inside a function to create a local parameter. Note that special
    parameters (e.g., $$, $!) can't be scoped in this
  way.
The exit status of a function is that of the last command executed
    in the function. A function can be made to finish immediately using the
    return command; this may also be used to explicitly specify the exit
    status.
Functions defined with the function reserved word are
    treated differently in the following ways from functions defined with the
    () notation:
  -   •
- the $0 parameter is set to the name of the function (Bourne-style
      functions leave $0 untouched).
-   •
- parameter assignments preceding function calls are not kept in the shell
      environment (executing Bourne-style functions will keep assignments).
-   •
- OPTIND is saved/reset and restored on entry and exit from the
      function so getopts can be used properly both inside and outside
      the function (Bourne-style functions leave OPTIND untouched, so
      using getopts inside a function interferes with using
      getopts outside the function). In the future, the following
      differences will also be added:
-   •
- A separate trap/signal environment will be used during the execution of
      functions. This will mean that traps set inside a function will not affect
      the shell's traps and signals that are not ignored in the shell (but may
      be trapped) will have their default effect in a function.
-   •
- The EXIT trap, if set in a function, will be executed after the function
      returns.
The shell is intended to be POSIX compliant, however, in some cases, POSIX
  behaviour is contrary either to the original Korn shell behaviour or to user
  convenience. How the shell behaves in these cases is determined by the state
  of the posix option (set -o posix) — if it is on, the POSIX
  behaviour is followed, otherwise it is not. The posix option is set
  automatically when the shell starts up if the environment contains the
  POSIXLY_CORRECT parameter. (The shell can also be compiled so that it
  is in POSIX mode by default, however this is usually not desirable).The following is a list of things that are affected by the state
    of the posix option:
  -   •
- kill -l output: in posix mode, signal names are listed one a single
      line; in non-posix mode, signal numbers, names and descriptions are
      printed in columns. In future, a new option (-v perhaps) will be
      added to distinguish the two behaviours.
-   •
- fg exit status: in posix mode, the exit status is 0 if no errors
      occur; in non-posix mode, the exit status is that of the last foregrounded
      job.
-   •
- eval exit status: if eval gets to see an empty command
      (e.g., eval "`false`"), its exit status in posix
      mode will be 0. In non-posix mode, it will be the exit status of the last
      command substitution that was done in the processing of the arguments to
      eval (or 0 if there were no command substitutions).
-   •
- getopts: in posix mode, options must start with a -; in
      non-posix mode, options can start with either - or +.
-   •
- brace expansion (also known as alternation): in posix mode, brace
      expansion is disabled; in non-posix mode, brace expansion enabled. Note
      that set -o posix (or setting the POSIXLY_CORRECT parameter)
      automatically turns the braceexpand option off, however it can be
      explicitly turned on later.
-   •
- set -: in posix mode, this does not clear the verbose or
      xtrace options; in non-posix mode, it does.
-   •
- set exit status: in posix mode, the exit status of set is 0 if
      there are no errors; in non-posix mode, the exit status is that of any
      command substitutions performed in generating the set command. For
      example, `set -- `false`; echo $?' prints 0 in posix mode, 1 in
      non-posix mode. This construct is used in most shell scripts that use the
      old getopt(1) command.
-   •
- argument expansion of alias, export, readonly, and
      typeset commands: in posix mode, normal argument expansion done; in
      non-posix mode, field splitting, file globing, brace expansion and
      (normal) tilde expansion are turned off, and assignment tilde expansion is
      turned on.
-   •
- signal specification: in posix mode, signals can be specified as digits
      only if signal numbers match POSIX values (i.e., HUP=1, INT=2,
      QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15); in non-posix mode, signals
      can be always digits.
-   •
- alias expansion: in posix mode, alias expansion is only carried out when
      reading command words; in non-posix mode, alias expansion is carried out
      on any word following an alias that ended in a space. For example, the
      following for loop
alias a='for ' i='j'
a i in 1 2; do echo i=$i j=$j; done 
uses parameter i in posix mode, j in non-posix
  mode.
  -   •
- test: in posix mode, the expression "-t" (preceded by
      some number of "!" arguments) is always true as it is a
      non-zero length string; in non-posix mode, it tests if file descriptor 1
      is a tty (i.e., the fd argument to the -t test may be
      left out and defaults to 1).
After evaluation of command line arguments, redirections and parameter
  assignments, the type of command is determined: a special built-in, a
  function, a regular built-in or the name of a file to execute found using the
  PATH parameter. The checks are made in the above order. Special
  built-in commands differ from other commands in that the PATH parameter
  is not used to find them, an error during their execution can cause a
  non-interactive shell to exit and parameter assignments that are specified
  before the command are kept after the command completes. Just to confuse
  things, if the posix option is turned off (see set command below) some
  special commands are very special in that no field splitting, file globing,
  brace expansion nor tilde expansion is performed on arguments that look like
  assignments. Regular built-in commands are different only in that the
  PATH parameter is not used to find them.The original ksh and POSIX differ somewhat in which commands are
    considered special or regular:
  - POSIX special commands
- 
    
      
        | . | continue | exit | return | trap |  
        | : | eval | export | set | unset |  
        | break | exec | readonly | shift |  
 
- Additional ksh special commands
- 
    
  
- Very special commands (non-posix mode)
- 
    
      
        | alias | readonly | set | typeset |  
 
- POSIX regular commands
- 
    
      
        | alias | command | fg | kill | umask |  
        | bg | false | getopts | read | unalias |  
        | cd | fc | jobs | true | wait |  
 
- Additional ksh regular commands
- 
    
      
        | [ | let | pwd | ulimit |  
        | echo | print | test | whence |  
 
In the future, the additional ksh special and regular commands may
    be treated differently from the POSIX special and regular commands.
Once the type of the command has been determined, any command line
    parameter assignments are performed and exported for the duration of the
    command.
The following describes the special and regular built-in
  commands:
  - . file [arg1 ...]
- Execute the commands in file in the current environment. The file
      is searched for in the directories of PATH. If arguments are given,
      the positional parameters may be used to access them while file is
      being executed. If no arguments are given, the positional parameters are
      those of the environment the command is used in.
- : [ ... ]
- The null command. Exit status is set to zero.
- alias [ -d | ±t [-r] ]
    [±px] [±] [name1[=value1]
    ...]
- Without arguments, alias lists all aliases. For any name without a
      value, the existing alias is listed. Any name with a value defines an
      alias (see Aliases above).
    When listing aliases, one of two formats is used: normally,
        aliases are listed as name=value, where
        value is quoted; if options were preceded with + or a lone
        + is given on the command line, only name is printed. In
        addition, if the -p option is used, each alias is prefixed with
        the string "alias ". The -x option sets (+x clears) the export
        attribute of an alias, or, if no names are given, lists the aliases with
        the export attribute (exporting an alias has no affect). The -t option indicates that tracked aliases are to be
        listed/set (values specified on the command line are ignored for tracked
        aliases). The -r option indicates that all tracked aliases are to
        be reset. The -d causes directory aliases, which are used in
        tilde expansion, to be listed or set (see Tilde Expansion above). 
- bg [job ...]
- Resume the specified stopped job(s) in the background. If no jobs are
      specified, %+ is assumed. This command is only available on systems
      which support job control. See Job Control below for more
    information.
- bind [-l] [-m]
    [key[=editing-command] ...]
- Set or view the current emacs command editing key bindings/macros. See
      Emacs Editing Mode below for a complete description.
- break [level]
- break exits the levelth inner most for, select, until, or
      while loop. level defaults to 1.
- builtin command [arg1 ...]
- Execute the built-in command command.
- cd [-LP] [dir]
- Set the working directory to dir. If the parameter CDPATH is
      set, it lists directories to search in for dir. An empty entry in
      the CDPATH entry means the current directory. If a non-empty
      directory from CDPATH is used, the resulting full path is printed
      to standard output. If dir is missing, the home directory
      $HOME is used. If dir is -, the previous working
      directory is used (see OLDPWD parameter). If -L option (logical
      path) is used or if the physical option (see set command
      below) isn't set, references to .. in dir are relative to
      the path used get to the directory. If -P option (physical path) is
      used or if the physical option is set, .. is relative to the
      filesystem directory tree. The PWD and OLDPWD parameters are
      updated to reflect the current and old wording directory,
    respectively.
- cd [-LP] old new
- The string new is substituted for old in the current
      directory, and the shell attempts to change to the new directory.
- command [-pvV] cmd [arg1 ...]
- If neither the -v nor -V options are given, cmd is
      executed exactly as if the command had not been specified, with two
      exceptions: first, cmd cannot be a shell function, and second,
      special built-in commands lose their specialness (i.e., redirection
      and utility errors do not cause the shell to exit, and command assignments
      are not permanent). If the -p option is given, a default search
      path is used instead of the current value of PATH (the actual value
      of the default path is system dependent: on POSIXish systems, it is the
      value returned by
    
 getconf CS_PATH
 ).If the -v option is given, instead of executing
        cmd, information about what would be executed is given (and the
        same is done for arg1 ...): for special and regular built-in
        commands and functions, their names are simply printed, for aliases, a
        command that defines them is printed, and for commands found by
        searching the PATH parameter, the full path of the command is
        printed. If no command is found, (i.e., the path search fails),
        nothing is printed and command exits with a non-zero status. The
        -V option is like the -v option, except it is more
        verbose. 
- continue [levels]
- continue jumps to the beginning of the levelth inner most
      for, select, until, or while loop. level defaults to 1.
- echo [-neE] [arg ...]
- Prints its arguments (separated by spaces) followed by a newline, to
      standard out. The newline is suppressed if any of the arguments contain
      the backslash sequence \c. See print command below for a
      list of other backslash sequences that are recognized.
    The options are provided for compatibility with BSD shell
        scripts: -n suppresses the trailing newline, -e enables
        backslash interpretation (a no-op, since this is normally done), and
        -E suppresses backslash interpretation. 
- eval command ...
- The arguments are concatenated (with spaces between them) to form a single
      string which the shell then parses and executes in the current
      environment.
- exec [command [arg ...]]
- The command is executed without forking, replacing the shell process.
    If no arguments are given, any IO redirection is permanent and
        the shell is not replaced. Any file descriptors greater than 2 which are
        opened or dup(2)-ed in this way are not made available to other
        executed commands (i.e., commands that are not built-in to the
        shell). Note that the Bourne shell differs here: it does pass these file
        descriptors on. 
- exit [status]
- The shell exits with the specified exit status. If status is not
      specified, the exit status is the current value of the ?
    parameter.
- export [-p] [parameter[=value]]
    ...
- Sets the export attribute of the named parameters. Exported parameters are
      passed in the environment to executed commands. If values are specified,
      the named parameters also assigned.
    If no parameters are specified, the names of all parameters
        with the export attribute are printed one per line, unless the -p
        option is used, in which case export commands defining all
        exported parameters, including their values, are printed. 
- false
- A command that exits with a non-zero status.
- fc [-e editor | -l [-n]] [-r]
    [first [last]]
- first and last select commands from the history. Commands
      can be selected by history number, or a string specifying the most recent
      command starting with that string. The -l option lists the command
      on stdout, and -n inhibits the default command numbers. The
      -r option reverses the order of the list. Without -l, the
      selected commands are edited by the editor specified with the -e
      option, or if no -e is specified, the editor specified by the
      FCEDIT parameter (if this parameter is not set, /bin/ed is
      used), and then executed by the shell.
- fc [-e - | -s] [-g]
    [old=new] [prefix]
- Re-execute the selected command (the previous command by default) after
      performing the optional substitution of old with new. If
      -g is specified, all occurrences of old are replaced with
      new. This command is usually accessed with the predefined alias
      r='fc -e -'.
- fg [job ...]
- Resume the specified job(s) in the foreground. If no jobs are specified,
      %+ is assumed. This command is only available on systems which
      support job control. See Job Control below for more information.
- getopts optstring name [arg ...]
- getopts is used by shell procedures to parse the specified
      arguments (or positional parameters, if no arguments are given) and to
      check for legal options. optstring contains the option letters that
      getopts is to recognize. If a letter is followed by a colon, the
      option is expected to have an argument. Options that do not take arguments
      may be grouped in a single argument. If an option takes an argument and
      the option character is not the last character of the argument it is found
      in, the remainder of the argument is taken to be the option's argument,
      otherwise, the next argument is the option's argument.
    Each time getopts is invoked, it places the next option
        in the shell parameter name and the index of the next argument to
        be processed in the shell parameter OPTIND. If the option was
        introduced with a +, the option placed in name is prefixed
        with a +. When an option requires an argument, getopts
        places it in the shell parameter OPTARG. When an illegal option
        or a missing option argument is encountered a question mark or a colon
        is placed in name (indicating an illegal option or missing
        argument, respectively) and OPTARG is set to the option character
        that caused the problem. An error message is also printed to standard
        error if optstring does not begin with a colon. When the end of the options is encountered, getopts
        exits with a non-zero exit status. Options end at the first (non-option)
        argument that does not start with a -, or when a -- argument is
        encountered. Option parsing can be reset by setting OPTIND to 1
        (this is done automatically whenever the shell or a shell procedure is
        invoked). Warning: Changing the value of the shell parameter
        OPTIND to a value other than 1, or parsing different sets of
        arguments without resetting OPTIND may lead to unexpected
        results. 
- hash [-r] [name ...]
- Without arguments, any hashed executable command pathnames are listed. The
      -r option causes all hashed commands to be removed from the hash
      table. Each name is searched as if it where a command name and
      added to the hash table if it is an executable command.
- jobs [-lpn] [job ...]
- Display information about the specified jobs; if no jobs are specified,
      all jobs are displayed. The -n option causes information to be
      displayed only for jobs that have changed state since the last
      notification. If the -l option is used, the process-id of each
      process in a job is also listed. The -p option causes only the
      process group of each job to be printed. See Job Control below for the
      format of job and the displayed job.
- kill [-s signame | -signum | -signame ]
    { job | pid | -pgrp } ...
- Send the specified signal to the specified jobs, process ids, or process
      groups. If no signal is specified, the signal TERM is sent. If a job is
      specified, the signal is sent to the job's process group. See Job Control
      below for the format of job.
- kill -l [exit-status ...]
- Print the name of the signal that killed a process which exited with the
      specified exit-statuses. If no arguments are specified, a list of
      all the signals, their numbers and a short description of them are
      printed.
- let [expression ...]
- Each expression is evaluated, see Arithmetic Expressions above. If all
      expressions are successfully evaluated, the exit status is 0 (1) if the
      last expression evaluated to non-zero (zero). If an error occurs during
      the parsing or evaluation of an expression, the exit status is greater
      than 1. Since expressions may need to be quoted, (( expr
      )) is syntactic sugar for let
      "expr".
- print [-nprsun | -R [-en]] [argument
    ...]
- Print prints its arguments on the standard output, separated by
      spaces, and terminated with a newline. The -n option suppresses the
      newline. By default, certain C escapes are translated. These include \b,
      \f, \n, \r, \t, \v, and \0### (# is an octal digit, of which there may be
      0 to 3). \c is equivalent to using the -n option. \ expansion may
      be inhibited with the -r option. The -s option prints to the
      history file instead of standard output, the -u option prints to
      file descriptor n (n defaults to 1 if omitted), and the
      -p option prints to the co-process (see Co-Processes above).
    The -R option is used to emulate, to some degree, the
        BSD echo command, which does not process \ sequences unless the
        -e option is given. As above, the -n option suppresses the
        trailing newline. 
- pwd [-LP]
- Print the present working directory. If -L option is used or if the
      physical option (see set command below) isn't set, the
      logical path is printed (i.e., the path used to cd to the
      current directory). If -P option (physical path) is used or if the
      physical option is set, the path determined from the filesystem (by
      following .. directories to the root directory) is printed.
- read [-prsun] [parameter ...]
- Reads a line of input from standard input, separate the line into fields
      using the IFS parameter (see Substitution above), and assign each
      field to the specified parameters. If there are more parameters than
      fields, the extra parameters are set to null, or alternatively, if there
      are more fields than parameters, the last parameter is assigned the
      remaining fields (inclusive of any separating spaces). If no parameters
      are specified, the REPLY parameter is used. If the input line ends
      in a backslash and the -r option was not used, the backslash and
      newline are stripped and more input is read. If no input is read,
      read exits with a non-zero status.
    The first parameter may have a question mark and a string
        appended to it, in which case the string is used as a prompt (printed to
        standard error before any input is read) if the input is a tty
        (e.g., read nfoo?'number of foos: '). The -un and -p options cause input to be
        read from file descriptor n or the current co-process (see
        Co-Processes above for comments on this), respectively. If the -s
        option is used, input is saved to the history file. 
- readonly [-p] [parameter[=value]]
    ...
- Sets the readonly attribute of the named parameters. If values are given,
      parameters are set to them before setting the attribute. Once a parameter
      is made readonly, it cannot be unset and its value cannot be changed.
    If no parameters are specified, the names of all parameters
        with the readonly attribute are printed one per line, unless the
        -p option is used, in which case readonly commands
        defining all readonly parameters, including their values, are
      printed. 
- return [status]
- Returns from a function or . script, with exit status
      status. If no status is given, the exit status of the last
      executed command is used. If used outside of a function or .
      script, it has the same effect as exit. Note that pdksh treats both
      profile and $ENV files as . scripts, while the original Korn
      shell only treats profiles as . scripts.
- set [±abCefhkmnpsuvxX] [±o
    [option]] [±A name] [--] [arg
    ...]
- The set command can be used to set (-) or clear (+) shell
      options, set the positional parameters, or set an array parameter. Options
      can be changed using the ±o option syntax, where
      option is the long name of an option, or using the
      ±letter syntax, where letter is the option's
      single letter name (not all options have a single letter name). The
      following table lists both option letters (if they exist) and long names
      along with a description of what the option does.
    
    
      
        | -A |  | Sets the elements of the array parameter name to arg
          ...; If -A is used, the array is reset (i.e., emptied)
          first; if +A is used, the first N elements are set (where N is
          the number of args), the rest are left untouched. |  
        | -a | allexport | all new parameters are created with the export attribute |  
        | -b | notify | Print job notification messages asynchronously, instead of just
          before the prompt. Only used if job control is enabled
          (-m). |  
        | -C | noclobber | Prevent > redirection from overwriting existing files
          (>| must be used to force an overwrite). |  
        | -e | errexit | Exit (after executing the ERR trap) as soon as an error
          occurs or a command fails (i.e., exits with a non-zero status).
          This does not apply to commands whose exit status is explicitly tested
          by a shell construct such as if, until, while,
          && or || statements. |  
        | -f | noglob | Do not expand file name patterns. |  
        | -h | trackall | Create tracked aliases for all executed commands (see Aliases
          above). On by default for non-interactive shells. |  
        | -i | interactive | Enable interactive mode - this can only be set/unset when the shell
          is invoked. |  
        | -k | keyword | Parameter assignments are recognized anywhere in a command. |  
        | -l | login | The shell is a login shell - this can only be set/unset when the
          shell is invoked (see Shell Startup above). |  
        | -m | monitor | Enable job control (default for interactive shells). |  
        | -n | noexec | Do not execute any commands - useful for checking the syntax of
          scripts (ignored if interactive). |  
        | -p | privileged | Set automatically if, when the shell starts, the real uid or gid
          does not match the effective uid or gid, respectively. See Shell
          Startup above for a description of what this means. |  
        | -r | restricted | Enable restricted mode — this option can only be used when
          the shell is invoked. See Shell Startup above for a description of
          what this means. |  
        | -s | stdin | If used when the shell is invoked, commands are read from standard
          input. Set automatically if the shell is invoked with no arguments.
          When -s is used in the set command, it causes the
          specified arguments to be sorted before assigning them to the
          positional parameters (or to array name, if -A is
          used). |  
        | -u | nounset | Referencing of an unset parameter is treated as an error, unless one
          of the -, + or = modifiers is used. |  
        | -v | verbose | Write shell input to standard error as it is read. |  
        | -x | xtrace | Print commands and parameter assignments when they are executed,
          preceded by the value of PS4. |  
        | -X | markdirs | Mark directories with a trailing / during file name
          generation. |  
        |  | bgnice | Background jobs are run with lower priority. |  
        |  | braceexpand | Enable brace expansion (aka, alternation). |  
        |  | emacs | Enable BRL emacs-like command line editing (interactive shells
          only); see Emacs Editing Mode. |  
        |  | emacs-usemeta | In emacs command-line editing, use the 8th bit as meta (^[) prefix.
          This is the default if LC_CTYPE is unset or POSIX respectively C. 8 |  
        |  | gmacs | Enable gmacs-like (Gosling emacs) command line editing (interactive
          shells only); currently identical to emacs editing except that
          transpose (^T) acts slightly differently. |  
        |  | ignoreeof | The shell will not (easily) exit on when end-of-file is read,
          exit must be used. To avoid infinite loops, the shell will exit
          if eof is read 13 times in a row. |  
        |  | nohup | Do not kill running jobs with a HUP signal when a login shell
          exists. Currently set by default, but this will change in the future
          to be compatible with the original Korn shell (which doesn't have this
          option, but does send the HUP signal). |  
        |  | nolog | No effect - in the original Korn shell, this prevents function
          definitions from being stored in the history file. |  
        |  | physical | Causes the cd and pwd commands to use `physical'
          (i.e., the filesystem's) .. directories instead of
          `logical' directories (i.e., the shell handles .., which
          allows the user to be oblivious of symlink links to directories).
          Clear by default. Note that setting this option does not effect the
          current value of the PWD parameter; only the cd command
          changes PWD. See the cd and pwd commands above
          for more details. |  
        |  | posix | Enable posix mode. See POSIX Mode above. |  
        |  | vi | Enable vi-like command line editing (interactive shells only). |  
        |  | viraw | No effect - in the original Korn shell, unless viraw was set, the vi
          command line mode would let the tty driver do the work until ESC (^[)
          was entered. pdksh is always in viraw mode. |  
        |  | vi-esccomplete | In vi command line editing, do command / file name completion when
          escape (^[) is entered in command mode. |  
        |  | vi-show8 | Prefix characters with the eighth bit set with `M-'. If this option
          is not set, characters in the range 128-160 are printed as is, which
          may cause problems. |  
        |  | vi-tabcomplete | In vi command line editing, do command / file name completion when
          tab (^I) is entered in insert mode. This is the default. |  
 These options can also be used upon invocation of the shell.
        The current set of options (with single letter names) can be found in
        the parameter -. set -o with no option name will list all
        the options and whether each is on or off; set +o will print the
        long names of all options that are currently on. Remaining arguments, if any, are positional parameters and are
        assigned, in order, to the positional parameters (i.e., 1,
        2, etc.). If options are ended with -- and there
        are no remaining arguments, all positional parameters are cleared. If no
        options or arguments are given, then the values of all names are
        printed. For unknown historical reasons, a lone - option is
        treated specially: it clears both the -x and -v
      options. 
- shift [number]
- The positional parameters number+1, number+2 etc. are
      renamed to 1, 2, etc. number defaults to
    1.
- test expression
- [ expression ]
- test evaluates the expression and returns zero status if
      true, 1 if false, and greater than 1 if there was an error. It is normally
      used as the condition command of if and while statements.
      The following basic expressions are available:
    
    
      
        | str | str has non-zero length. Note
          that there is the potential for problems if str turns out to be
          an operator (e.g., -r) - it is generally better to use a
          test like [ X"str" != X ] instead
          (double quotes are used in case str contains spaces or file
          globing characters). |  
        | -r file | file exists and is
          readable. |  
        | -w file | file exists and is
          writable. |  
        | -x file | file exists and is
          executable. |  
        | -a file | file exists. |  
        | -e file | file exists. |  
        | -f file | file is a regular file. |  
        | -d file | file is a directory. |  
        | -c file | file is a character special
          device. |  
        | -b file | file is a block special
          device. |  
        | -p file | file is a named pipe. |  
        | -u file | file's mode has setuid bit
          set. |  
        | -g file | file's mode has setgid bit
          set. |  
        | -k file | file's mode has sticky bit
          set. |  
        | -s file | file is not empty. |  
        | -O file | file's owner is the shell's
          effective user-ID. |  
        | -G file | file's group is the shell's
          effective group-ID. |  
        | -h file | file is a symbolic link. |  
        | -H file | file is a context dependent
          directory (only useful on HP-UX). |  
        | -L file | file is a symbolic link. |  
        | -S file | file is a socket. |  
        | -o option | shell option is set (see
          set command above for list of options). As a non-standard
          extension, if the option starts with a !, the test is negated;
          the test always fails if option doesn't exist (thus [ -o
          foo -o -o !foo ] returns true if and
          only if option foo exists). |  
        | file -nt file | first file is newer than second
          file or first file exists and the second file
          does not. |  
        | file -ot file | first file is older than second
          file or second file exists and the first file
          does not. |  
        | file -ef file | first file is the same file as
          second file. |  
        | -t [fd] | file descriptor is a tty device. If the
          posix option (set -o posix, see POSIX Mode above) is not set,
          fd may be left out, in which case it is taken to be 1 (the
          behaviour differs due to the special POSIX rules described
          below). |  
        | string | string is not empty. |  
        | -z string | string is empty. |  
        | -n string | string is not empty. |  
        | string = string | strings are equal. |  
        | string == string | strings are equal. |  
        | string != string | strings are not equal. |  
        | number -eq number | numbers compare equal. |  
        | number -ne number | numbers compare not equal. |  
        | number -ge number | numbers compare greater than or
          equal. |  
        | number -gt number | numbers compare greater than. |  
        | number -le number | numbers compare less than or
          equal. |  
        | number -lt number | numbers compare less than. |  
 The above basic expressions, in which unary operators have
        precedence over binary operators, may be combined with the following
        operators (listed in increasing order of precedence): 
      
        | expr -o expr | logical or |  
        | expr -a expr | logical and |  
        | ! expr | logical not |  
        | ( expr ) | grouping |  
 On operating systems not supporting /dev/fd/n
        devices (where n is a file descriptor number), the test
        command will attempt to fake it for all tests that operate on files
        (except the -e test). I.e., [ -w /dev/fd/2 ] tests if file
        descriptor 2 is writable. Note that some special rules are applied (courtesy of POSIX)
        if the number of arguments to test or [ ... ] is
        less than five: if leading ! arguments can be stripped such that
        only one argument remains then a string length test is performed (again,
        even if the argument is a unary operator); if leading ! arguments
        can be stripped such that three arguments remain and the second argument
        is a binary operator, then the binary operation is performed (even if
        first argument is a unary operator, including an unstripped
      !). Note: A common mistake is to use if [ $foo = bar
        ] which fails if parameter foo is null or unset, if it has
        embedded spaces (i.e., IFS characters), or if it is a
        unary operator like ! or -n. Use tests like if [
        "X$foo" = Xbar ] instead. 
- time [-p] [ pipeline ]
- If a pipeline is given, the times used to execute the pipeline are
      reported. If no pipeline is given, then the user and system time used by
      the shell itself, and all the commands it has run since it was started,
      are reported. The times reported are the real time (elapsed time from
      start to finish), the user CPU time (time spent running in user mode) and
      the system CPU time (time spent running in kernel mode). Times are
      reported to standard error; the format of the output is:
    
    0.00s real     0.00s user     0.00s system
    unless the -p option is given (only possible if pipeline is a simple
      command), in which case the output is slightly longer:
    real   0.00
    user   0.00
    sys    0.00
    (the number of digits after the decimal may vary from system to system).
      Note that simple redirections of standard error do not effect the output
      of the time command:
 time sleep 1 2> afile
 
 { time sleep 1; } 2> afile
 times for the first command do not go to afile, but those of the
      second command do.
- times
- Print the accumulated user and system times used by the shell and by
      processes which have exited that the shell started.
- trap [handler signal ...]
- Sets trap handler that is to be executed when any of the specified signals
      are received. Handler is either a null string, indicating the
      signals are to be ignored, a minus (-), indicating that the default
      action is to be taken for the signals (see signal(3)), or a string
      containing shell commands to be evaluated and executed at the first
      opportunity (i.e., when the current command completes, or before
      printing the next PS1 prompt) after receipt of one of the signals.
      Signal is the name of a signal (e.g., PIPE or ALRM) or the
      number of the signal (see kill -l command above). There are two
      special signals: EXIT (also known as 0), which is executed
      when the shell is about to exit, and ERR which is executed after an
      error occurs (an error is something that would cause the shell to exit if
      the -e or errexit option were set — see set
      command above). EXIT handlers are executed in the environment of
      the last executed command. Note that for non-interactive shells, the trap
      handler cannot be changed for signals that were ignored when the shell
      started.
    With no arguments, trap lists, as a series of
        trap commands, the current state of the traps that have been set
        since the shell started. Note that the output of trap can not be
        usefully piped to another process (an artifact of the fact that traps
        are cleared when subprocesses are created). The original Korn shell's DEBUG trap and the handling
        of ERR and EXIT traps in functions are not yet
        implemented. 
- true
- A command that exits with a zero value.
- typeset [[±Ulprtux] [-L[n]]
    [-R[n]] [-Z[n]] [-i[n]] |
    -f [-tux]] [name[=value] ...]
- Display or set parameter attributes. With no name arguments,
      parameter attributes are displayed: if no options arg used, the current
      attributes of all parameters are printed as typeset commands; if an option
      is given (or - with no option letter) all parameters and their
      values with the specified attributes are printed; if options are
      introduced with +, parameter values are not printed.
    If name arguments are given, the attributes of the
        named parameters are set (-) or cleared (+). Values for
        parameters may optionally be specified. If typeset is used inside a
        function, any newly created parameters are local to the function. When -f is used, typeset operates on the attributes of
        functions. As with parameters, if no names are given, functions
        are listed with their values (i.e., definitions) unless options
        are introduced with +, in which case only the function names are
        reported. 
      
        | -Ln | Left justify attribute: n specifies the field width. If
          n is not specified, the current width of a parameter (or the
          width of its first assigned value) is used. Leading white space (and
          zeros, if used with the -Z option) is stripped. If necessary,
          values are either truncated or space padded to fit the field
          width. |  
        | -Rn | Right justify attribute: n specifies the field width. If
          n is not specified, the current width of a parameter (or the
          width of its first assigned value) is used. Trailing white space are
          stripped. If necessary, values are either stripped of leading
          characters or space padded to make them fit the field width. |  
        | -Zn | Zero fill attribute: if not combined with -L, this is the
          same as -R, except zero padding is used instead of space
          padding. |  
        | -in | integer attribute: n specifies the base to use when
          displaying the integer (if not specified, the base given in the first
          assignment is used). Parameters with this attribute may be assigned
          values containing arithmetic expressions. |  
        | -U | unsigned integer attribute: integers are printed as unsigned values
          (only useful when combined with the -i option). This option is
          not in the original Korn shell. |  
        | -f | Function mode: display or set functions and their attributes,
          instead of parameters. |  
        | -l | Lower case attribute: all upper case characters in values are
          converted to lower case. (In the original Korn shell, this parameter
          meant `long integer' when used with the -i option). |  
        | -p | Print complete typeset commands that can be used to re-create the
          attributes (but not the values) of parameters. This is the default
          action (option exists for ksh93 compatibility). |  
        | -r | Readonly attribute: parameters with the this attribute may not be
          assigned to or unset. Once this attribute is set, it can not be turned
          off. |  
        | -t | Tag attribute: has no meaning to the shell; provided for application
          use. For functions, -t is the trace attribute. When functions
          with the trace attribute are executed, the xtrace (-x)
          shell option is temporarily turned on. |  
        | -u | Upper case attribute: all lower case characters in values are
          converted to upper case. (In the original Korn shell, this parameter
          meant `unsigned integer' when used with the -i option, which
          meant upper case letters would never be used for bases greater than
          10. See the -U option). For functions, -u is the
          undefined attribute. See Functions above for the implications of
          this. |  
        | -x | Export attribute: parameters (or functions) are placed in the
          environment of any executed commands. Exported functions are not
          implemented yet. |  
 
- ulimit [-abcdfHlmnprsStvw] [value]
- Display or set process limits. If no options are used, the file size limit
      (-f) is assumed. value, if specified, may be either be an
      arithmetic expression or the word unlimited. The limits affect the
      shell and any processes created by the shell after a limit is imposed.
      Note that some systems may not allow limits to be increased once they are
      set. Also note that the types of limits available are system dependent -
      some systems have only the -f limit.
  - -a
- Displays all limits; unless -H is used, soft limits are
    displayed.
- -H
- Set the hard limit only (default is to set both hard and soft
    limits).
- -S
- Set the soft limit only (default is to set both hard and soft
    limits).
- -b
- Impose a size limit of n bytes on the size of socket buffers.
- -c
- Impose a size limit of n blocks on the size of core dumps.
- -d
- Impose a size limit of n kbytes on the size of the data area.
- -f
- Impose a size limit of n blocks on files written by the shell and
      its child processes (files of any size may be read).
- -l
- Impose a limit of n kbytes on the amount of locked (wired) physical
      memory.
- -m
- Impose a limit of n kbytes on the amount of physical memory
    used.
- -n
- Impose a limit of n file descriptors that can be open at once.
- -r
- Impose a limit of n threads that can be run by the user at any one
      time.
- -p
- Impose a limit of n processes that can be run by the user at any
      one time.
- -s
- Impose a size limit of n kbytes on the size of the stack area.
- -t
- Impose a time limit of n CPU seconds to be used by each
    process.
- -v
- Impose a limit of n kbytes on the amount of virtual memory used; on
      some systems this is the maximum allowable virtual address (in bytes, not
      kbytes).
- -w
- Impose a limit of n kbytes on the amount of swap space used. (Not
      supported on NetBSD)
As far as ulimit is concerned, a block is 512 bytes.
 
  - umask [-S] [mask]
Display or set the file permission creation mask, or
  umask (see 
umask(2)). If the 
-S option is used, the mask
  displayed or set is symbolic, otherwise it is an octal number.
Symbolic masks are like those used by chmod(1):
[ugoa]{{=+-}{rwx}*}+[,...]
in which the first group of characters is the 
who part, the second group
  is the 
op part, and the last group is the 
perm part. The
  
who part specifies which part of the umask is to be modified. The
  letters mean:
  - u
- the user permissions
- g
- the group permissions
- o
- the other permissions (non-user, non-group)
- a
- all permissions (user, group and other)
 
The op part indicates how the who permissions are to
    be modified:
  - =
- set
- +
- added to
- -
- removed from
 
The perm part specifies which permissions are to be set,
    added or removed:
  - r
- read permission
- w
- write permission
- x
- execute permission
 
When symbolic masks are used, they describe what permissions may
    be made available (as opposed to octal masks in which a set bit means the
    corresponding bit is to be cleared). Example: `ug=rwx,o=' sets the mask so
    files will not be readable, writable or executable by `others', and is
    equivalent (on most systems) to the octal mask `07'.
  - unalias [-adt] [name1 ...]
- The aliases for the given names are removed. If the -a option is
      used, all aliases are removed. If the -t or -d options are
      used, the indicated operations are carried out on tracked or directory
      aliases, respectively.
- unset [-fv] parameter ...
- Unset the named parameters (-v, the default) or functions
      (-f). The exit status is non-zero if any of the parameters were
      already unset, zero otherwise.
- wait [job]
- Wait for the specified job(s) to finish. The exit status of wait is that
      of the last specified job: if the last job is killed by a signal, the exit
      status is 128 + the number of the signal (see kill -l
      exit-status above); if the last specified job can't be found
      (because it never existed, or had already finished), the exit status of
      wait is 127. See Job Control below for the format of job.
      Wait will return if a signal for which a trap has been set is
      received, or if a HUP, INT or QUIT signal is received.
    If no jobs are specified, wait waits for all currently
        running jobs (if any) to finish and exits with a zero status. If job
        monitoring is enabled, the completion status of jobs is printed (this is
        not the case when jobs are explicitly specified). 
- whence [-pv] [name ...]
- For each name, the type of command is listed (reserved word, built-in,
      alias, function, tracked alias or executable). If the -p option is
      used, a path search done even if name is a reserved word, alias,
      etc. Without the -v option, whence is similar to
      command -v except that whence will find reserved words and
      won't print aliases as alias commands; with the -v option,
      whence is the same as command -V. Note that for
      whence, the -p option does not affect the search path used,
      as it does for command. If the type of one or more of the names
      could not be determined, the exit status is non-zero.
Job control refers to the shell's ability to monitor and control jobs,
  which are processes or groups of processes created for commands or pipelines.
  At a minimum, the shell keeps track of the status of the background
  (i.e., asynchronous) jobs that currently exist; this information can be
  displayed using the jobs command. If job control is fully enabled
  (using set -m or set -o monitor), as it is for interactive
  shells, the processes of a job are placed in their own process group,
  foreground jobs can be stopped by typing the suspend character from the
  terminal (normally ^Z), jobs can be restarted in either the foreground or
  background, using the fg and bg commands, respectively, and the
  state of the terminal is saved or restored when a foreground job is stopped or
  restarted, respectively.Note that only commands that create processes (e.g.,
    asynchronous commands, subshell commands, and non-built-in, non-function
    commands) can be stopped; commands like read cannot be.
When a job is created, it is assigned a job-number. For
    interactive shells, this number is printed inside [..],
    followed by the process-ids of the processes in the job when an asynchronous
    command is run. A job may be referred to in bg, fg,
    jobs, kill and wait commands either by the process id
    of the last process in the command pipeline (as stored in the $!
    parameter) or by prefixing the job-number with a percent sign (%).
    Other percent sequences can also be used to refer to jobs:
  
    | %+ | The most recently stopped job, or, if there are no stopped jobs, the
      oldest running job. | 
  
    | %%, % | Same as %+. | 
  
    | %- | The job that would be the %+ job, if the later did not
      exist. | 
  
    | %n | The job with job-number n. | 
  
    | %?string | The job containing the string string (an error occurs if multiple
      jobs are matched). | 
  
    | %string | The job starting with string string (an error occurs if multiple
      jobs are matched). | 
When a job changes state (e.g., a background job finishes
    or foreground job is stopped), the shell prints the following status
    information:
[number] flag status
  command
where
  -  number
- is the job-number of the job.
-  flag
- is + or - if the job is the %+ or %- job,
      respectively, or space if it is neither.
-  status
- indicates the current state of the job and can be
  - Running
- the job has neither stopped or exited (note that running does not
      necessarily mean consuming CPU time — the process could be blocked
      waiting for some event).
- Done [(number)]
- the job exited. number is the exit status of the job, which is
      omitted if the status is zero.
- Stopped [(signal)]
- the job was stopped by the indicated signal (if no signal is given,
      the job was stopped by SIGTSTP).
- signal-description [(core dumped)]
- the job was killed by a signal (e.g., Memory fault, Hangup,
      etc. — use kill -l for a list of signal
      descriptions). The (core dumped) message indicates the
      process created a core file.
 
  -  command
- is the command that created the process. If there are multiple processes
      in the job, then each process will have a line showing its command
      and possibly its status, if it is different from the status of the
      previous process.
When an attempt is made to exit the shell while there are jobs in
    the stopped state, the shell warns the user that there are stopped jobs and
    does not exit. If another attempt is immediately made to exit the shell, the
    stopped jobs are sent a HUP signal and the shell exits. Similarly, if
    the nohup option is not set and there are running jobs when an
    attempt is made to exit a login shell, the shell warns the user and does not
    exit. If another attempt is immediately made to exit the shell, the running
    jobs are sent a HUP signal and the shell exits.
The shell supports three modes of reading command lines from a tty in an
  interactive session. Which is used is controlled by the emacs,
  gmacs and vi set options (at most one of these can be set
  at once). If none of these options is enabled, the shell simply reads lines
  using the normal tty driver. If the emacs or gmacs option is
  set, the shell allows emacs like editing of the command; similarly, if the
  vi option is set, the shell allows vi like editing of the command.
  These modes are described in detail in the following sections.
In these editing modes, if a line is longer that the screen width
    (see COLUMNS parameter), a >, + or <
    character is displayed in the last column indicating that there are more
    characters after, before and after, or before the current position,
    respectively. The line is scrolled horizontally as necessary.
When the emacs option is set, interactive input line editing is enabled.
  Warning: This mode is slightly different from the emacs mode in the
  original Korn shell and the 8th bit is stripped in emacs mode. In this mode
  various editing commands (typically bound to one or more control characters)
  cause immediate actions without waiting for a new-line. Several editing
  commands are bound to particular control characters when the shell is invoked;
  these bindings can be changed using the following commands:
  - bind
- The current bindings are listed.
- bind string=[editing-command]
- The specified editing command is bound to the given string, which
      should consist of a control character (which may be written using caret
      notation ^X), optionally preceded by one of the two prefix
      characters. Future input of the string will cause the editing
      command to be immediately invoked. Note that although only two prefix
      characters (usually ESC and ^X) are supported, some multi-character
      sequences can be supported. The following binds the arrow keys on an ANSI
      terminal, or xterm (these are in the default bindings). Of course some
      escape sequences won't work out quite this nicely:
    
  
bind '^[['=prefix-2
bind '^XA'=up-history
bind '^XB'=down-history
bind '^XC'=forward-char
bind '^XD'=backward-char
  - bind -l
- Lists the names of the functions to which keys may be bound.
- bind -m string=[substitute]
- The specified input string will afterwards be immediately replaced
      by the given substitute string, which may contain editing
    commands.
The following is a list of editing commands available. Each
    description starts with the name of the command, a n, if the command
    can be prefixed with a count, and any keys the command is bound to by
    default (written using caret notation, e.g., ASCII ESC character is
    written as ^[). A count prefix for a command is entered using the sequence
    ^[n, where n is a sequence of 1 or more digits; unless
    otherwise specified, if a count is omitted, it defaults to 1. Note that
    editing command names are used only with the bind command.
    Furthermore, many editing commands are useful only on terminals with a
    visible cursor. The default bindings were chosen to resemble corresponding
    EMACS key bindings. The users tty characters (e.g., ERASE) are bound
    to reasonable substitutes and override the default bindings.
  - abort ^G
- Useful as a response to a request for a search-history pattern in
      order to abort the search.
- auto-insert n
- Simply causes the character to appear as literal input. Most ordinary
      characters are bound to this.
- backward-char n ^B
- Moves the cursor backward n characters.
- backward-word n ^[B
- Moves the cursor backward to the beginning of a word; words consist of
      alphanumerics, underscore (_) and dollar ($).
- beginning-of-history ^[<
- Moves to the beginning of the history.
- beginning-of-line ^A
- Moves the cursor to the beginning of the edited input line.
- capitalize-word n ^[c, ^[C
- Uppercase the first character in the next n words, leaving the
      cursor past the end of the last word. If the current line does not begin
      with a comment character, one is added at the beginning of the line and
      the line is entered (as if return had been pressed), otherwise the
      existing comment characters are removed and the cursor is placed at the
      beginning of the line.
- complete ^[^[
- complete ^I
- Automatically completes as much as is unique of the command name or the
      file name containing the cursor. If the entire remaining command or file
      name is unique a space is printed after its completion, unless it is a
      directory name in which case / is appended. If there is no command
      or file name with the current partial word as its prefix, a bell character
      is output (usually causing a audio beep).
- complete-command ^X^[
- Automatically completes as much as is unique of the command name having
      the partial word up to the cursor as its prefix, as in the complete
      command described above.
- complete-file ^[^X
- Automatically completes as much as is unique of the file name having the
      partial word up to the cursor as its prefix, as in the complete
      command described above.
- complete-list ^[=
- List the possible completions for the current word.
- delete-char-backward n ERASE, ^?,
    ^H
- Deletes n characters before the cursor.
- delete-char-forward n
- Deletes n characters after the cursor.
- delete-word-backward n ^[ERASE, ^[^?,
    ^[^H, ^[h
- Deletes n words before the cursor.
- delete-word-forward n ^[d
- Deletes characters after the cursor up to the end of n words.
- down-history n ^N
- Scrolls the history buffer forward n lines (later). Each input line
      originally starts just after the last entry in the history buffer, so
      down-history is not useful until either search-history or
      up-history has been performed.
- downcase-word n ^[L, ^[l
- Lowercases the next n words.
- end-of-history ^[>
- Moves to the end of the history.
- end-of-line ^E
- Moves the cursor to the end of the input line.
- eot ^_
- Acts as an end-of-file; this is useful because edit-mode input disables
      normal terminal input canonicalization.
- eot-or-delete n ^D
- Acts as eot if alone on a line; otherwise acts as
    delete-char-forward.
- error
- Error (ring the bell).
- exchange-point-and-mark ^X^X
- Places the cursor where the mark is, and sets the mark to where the cursor
      was.
- expand-file ^[*
- Appends a * to the current word and replaces the word with the result of
      performing file globbing on the word. If no files match the pattern, the
      bell is rung.
- forward-char n ^F
- Moves the cursor forward n characters.
- forward-word n ^[f
- Moves the cursor forward to the end of the nth word.
- goto-history n ^[g
- Goes to history number n.
- kill-line KILL
- Deletes the entire input line.
- kill-region ^W
- Deletes the input between the cursor and the mark.
- kill-to-eol n ^K
- Deletes the input from the cursor to the end of the line if n is
      not specified, otherwise deletes characters between the cursor and column
      n.
- list ^[?
- Prints a sorted, columnated list of command names or file names (if any)
      that can complete the partial word containing the cursor. Directory names
      have / appended to them.
- list-command ^X?
- Prints a sorted, columnated list of command names (if any) that can
      complete the partial word containing the cursor.
- list-file ^X^Y
- Prints a sorted, columnated list of file names (if any) that can complete
      the partial word containing the cursor. File type indicators are appended
      as described under list above.
- newline ^J, ^M
- Causes the current input line to be processed by the shell. The current
      cursor position may be anywhere on the line.
- newline-and-next ^O
- Causes the current input line to be processed by the shell, and the next
      line from history becomes the current line. This is only useful after an
      up-history or search-history.
- no-op QUIT
- This does nothing.
- prefix-1 ^[
- Introduces a 2-character command sequence.
- prefix-2 ^X
- prefix-2 ^[[
- Introduces a 2-character command sequence.
- prev-hist-word n ^[., ^[_
- The last (nth) word of the previous command is inserted at the
      cursor.
- quote ^^
- The following character is taken literally rather than as an editing
      command.
- redraw ^L
- Reprints the prompt string and the current input line.
- search-character-backward n ^[^]
- Search backward in the current line for the nth occurrence of the
      next character typed.
- search-character-forward n ^]
- Search forward in the current line for the nth occurrence of the
      next character typed.
- search-history ^R
- Enter incremental search mode. The internal history list is searched
      backwards for commands matching the input. An initial ^ in the
      search string anchors the search. The abort key will leave search mode.
      Other commands will be executed after leaving search mode. Successive
      search-history commands continue searching backward to the next
      previous occurrence of the pattern. The history buffer retains only a
      finite number of lines; the oldest are discarded as necessary.
- set-mark-command ^[<space>
- Set the mark at the cursor position.
- stuff
- On systems supporting it, pushes the bound character back onto the
      terminal input where it may receive special processing by the terminal
      handler. This is useful for the BRL ^T mini-systat feature, for
      example.
- stuff-reset
- Acts like stuff, then aborts input the same as an interrupt.
- transpose-chars ^T
- If at the end of line, or if the gmacs option is set, this
      exchanges the two previous characters; otherwise, it exchanges the
      previous and current characters and moves the cursor one character to the
      right.
- up-history n ^P
- Scrolls the history buffer backward n lines (earlier).
- upcase-word n ^[U, ^[u
- Uppercases the next n words.
- version ^V
- Display the version of ksh. The current edit buffer is restored as soon as
      any key is pressed (the key is then processed, unless it is a space).
- yank ^Y
- Inserts the most recently killed text string at the current cursor
      position.
- yank-pop ^[y
- Immediately after a yank, replaces the inserted text string with
      the next previous killed text string.
The vi command line editor in ksh has basically the same commands as the vi
  editor (see vi(1)), with the following exceptions:
  -   •
- you start out in insert mode,
-   •
- there are file name and command completion commands (=, \,
      *, ^X, ^E, ^F and, optionally,
      <tab>),
-   •
- the _ command is different (in ksh it is the last argument command,
      in vi it goes to the start of the current line),
-   •
- the / and G commands move in the opposite direction as the
      j command
-   •
- and commands which don't make sense in a single line editor are not
      available (e.g., screen movement commands, ex : commands,
      etc.).
Note that the ^X stands for control-X; also
    <esc>, <space> and <tab> are used for
    escape, space and tab, respectively (no kidding).
Like vi, there are two modes: insert mode and command mode. In
    insert mode, most characters are simply put in the buffer at the current
    cursor position as they are typed, however, some characters are treated
    specially. In particular, the following characters are taken from current
    tty settings (see stty(1)) and have their usual meaning (normal
    values are in parentheses): kill (^U), erase (^?), werase
    (^W), eof (^D), intr (^C) and quit (^\). In
    addition to the above, the following characters are also treated specially
    in insert mode:
  
    | ^H | erases previous character | 
  
    | ^V | literal next: the next character typed is not treated specially (can be
      used to insert the characters being described here) | 
  
    | ^J ^M | end of line: the current line is read, parsed and executed by the
      shell | 
  
    | <esc> | puts the editor in command mode (see below) | 
  
    | ^E | command and file name enumeration (see below) | 
  
    | ^F | command and file name completion (see below). If used twice in a row,
      the list of possible completions is displayed; if used a third time, the
      completion is undone. | 
  
    | ^X | command and file name expansion (see below) | 
  
    | <tab> | optional file name and command completion (see ^F above), enabled
      with set -o vi-tabcomplete | 
In command mode, each character is interpreted as a command.
    Characters that don't correspond to commands, are illegal combinations of
    commands or are commands that can't be carried out all cause beeps. In the
    following command descriptions, a n indicates the command may be
    prefixed by a number (e.g., 10l moves right 10 characters); if
    no number prefix is used, n is assumed to be 1 unless otherwise
    specified. The term `current position' refers to the position between the
    cursor and the character preceding the cursor. A `word' is a sequence of
    letters, digits and underscore characters or a sequence of non-letter,
    non-digit, non-underscore, non-white-space characters (e.g.,
    ab2*&^ contains two words) and a `big-word' is a sequence of
    non-white-space characters.
  - Special ksh vi commands
- The following commands are not in, or are different from, the normal vi
      file editor:
  - n_
- insert a space followed by the nth big-word from the last command
      in the history at the current position and enter insert mode; if n
      is not specified, the last word is inserted.
- #
- insert the comment character (#) at the start of the current line
      and return the line to the shell (equivalent to I#^J).
- ng
- like G, except if n is not specified, it goes to the most
      recent remembered line.
- nv
- edit line n using the vi editor; if n is not specified, the
      current line is edited. The actual command executed is `fc -e
      ${VISUAL:-${EDITOR:-vi}} n'.
- * and ^X
- command or file name expansion is applied to the current big-word (with an
      appended *, if the word contains no file globing characters) - the
      big-word is replaced with the resulting words. If the current big-word is
      the first on the line (or follows one of the following characters:
      ;, |, &, (, )) and does not contain
      a slash (/) then command expansion is done, otherwise file name
      expansion is done. Command expansion will match the big-word against all
      aliases, functions and built-in commands as well as any executable files
      found by searching the directories in the PATH parameter. File name
      expansion matches the big-word against the files in the current directory.
      After expansion, the cursor is placed just past the last word and the
      editor is in insert mode.
- n\, n^F, n<tab> and
    n<esc>
- command/file name completion: replace the current big-word with the
      longest unique match obtained after performing command/file name
      expansion. <tab> is only recognized if the
      vi-tabcomplete option is set, while <esc> is only
      recognized if the vi-esccomplete option is set (see set -o).
      If n is specified, the nth possible completion is selected
      (as reported by the command/file name enumeration command).
- = and ^E
- command/file name enumeration: list all the commands or files that match
      the current big-word.
- ^V
- display the version of pdksh; it is displayed until another key is pressed
      (this key is ignored).
- @c
- macro expansion: execute the commands found in the alias _c.
 
  - Intra-line movement commands
  - nh and n^H
- move left n characters.
- nl and n<space>
- move right n characters.
- 0
- move to column 0.
- ^
- move to the first non white-space character.
- n|
- move to column n.
- $
- move to the last character.
- nb
- move back n words.
- nB
- move back n big-words.
- ne
- move forward to the end the word, n times.
- nE
- move forward to the end the big-word, n times.
- nw
- move forward n words.
- nW
- move forward n big-words.
- %
- find match: the editor looks forward for the nearest parenthesis, bracket
      or brace and then moves the to the matching parenthesis, bracket or
    brace.
- nfc
- move forward to the nth occurrence of the character c.
- nFc
- move backward to the nth occurrence of the character c.
- ntc
- move forward to just before the nth occurrence of the character
      c.
- nTc
- move backward to just before the nth occurrence of the character
      c.
- n;
- repeats the last f, F, t or T command.
- n,
- repeats the last f, F, t or T command, but
      moves in the opposite direction.
 
  - Inter-line movement commands
  - nj and n+ and n^N
- move to the nth next line in the history.
- nk and n- and n^P
- move to the nth previous line in the history.
- nG
- move to line n in the history; if n is not specified, the
      number first remembered line is used.
- ng
- like G, except if n is not specified, it goes to the most
      recent remembered line.
- n/string
- search backward through the history for the nth line containing
      string; if string starts with ^, the remainder of the
      string must appear at the start of the history line for it to match.
- n?string
- same as /, except it searches forward through the history.
- nn
- search for the nth occurrence of the last search string; the
      direction of the search is the same as the last search.
- nN
- search for the nth occurrence of the last search string; the
      direction of the search is the opposite of the last search.
 
  - Edit commands
  - na
- append text n times: goes into insert mode just after the current
      position. The append is only replicated if command mode is re-entered
      (i.e., <esc> is used).
- nA
- same as a, except it appends at the end of the line.
- ni
- insert text n times: goes into insert mode at the current position.
      The insertion is only replicated if command mode is re-entered
      (i.e., <esc> is used).
- nI
- same as i, except the insertion is done just before the first
      non-blank character.
- ns
- substitute the next n characters (i.e., delete the
      characters and go into insert mode).
- S
- substitute whole line: all characters from the first non-blank character
      to the end of line are deleted and insert mode is entered.
- ncmove-cmd
- change from the current position to the position resulting from n
      move-cmds (i.e., delete the indicated region and go into
      insert mode); if move-cmd is c, the line starting from the
      first non-blank character is changed.
- C
- change from the current position to the end of the line (i.e.,
      delete to the end of the line and go into insert mode).
- nx
- delete the next n characters.
- nX
- delete the previous n characters.
- D
- delete to the end of the line.
- ndmove-cmd
- delete from the current position to the position resulting from n
      move-cmds; move-cmd is a movement command (see above) or
      d, in which case the current line is deleted.
- nrc
- replace the next n characters with the character c.
- nR
- replace: enter insert mode but overwrite existing characters instead of
      inserting before existing characters. The replacement is repeated n
      times.
- n~
- change the case of the next n characters.
- nymove-cmd
- yank from the current position to the position resulting from n
      move-cmds into the yank buffer; if move-cmd is y, the
      whole line is yanked.
- Y
- yank from the current position to the end of the line.
- np
- paste the contents of the yank buffer just after the current position,
      n times.
- nP
- same as p, except the buffer is pasted at the current
    position.
 
  - Miscellaneous vi commands
  - ^J and ^M
- the current line is read, parsed and executed by the shell.
- ^L and ^R
- redraw the current line.
- n.
- redo the last edit command n times.
- u
- undo the last edit command.
- U
- undo all changes that have been made to the current line.
- intr and quit
- the interrupt and quit terminal characters cause the current line to be
      deleted and a new prompt to be printed.