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NAME    [Toc]    [Back]

     ksh - public domain Korn shell

SYNOPSIS    [Toc]    [Back]

     ksh [-+abCefhiklmnprsuvxX] [-+o option]
         [[-c  command-string  [command-name]  |   -s   |   file]
[argument ...]]

DESCRIPTION    [Toc]    [Back]

     ksh  is  a command interpreter intended for both interactive
and shell
     script use.  Its command language is a superset of the sh(1)
shell language.

   Shell startup    [Toc]    [Back]
     The  following  options can be specified only on the command

     -c command-string
             ksh  will  execute  the  command(s)   contained   in

     -i      Interactive mode; see below.

     -l      Login shell; 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 option is specified, the first
     argument specifies the name of a file the shell  reads  commands from.  If
     there  are no non-option arguments, the shell reads commands
from the
     standard input.  The name of the shell (i.e.,  the  contents
of $0) is determined
 as follows: if the -c option is used and there is a
     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  SIGINT,
     SIGTERM  signals,  and  prints  prompts before reading input
(see PS1 and PS2
     parameters).  For non-interactive shells, the  trackall  option is on by
     default (see the set command below).

     A shell is ``restricted'' if the -r option is used or if either the basename
 of the name the shell was 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:

     +o   The cd command is disabled.
     +o   The SHELL, ENV, and PATH parameters cannot be changed.
     +o    Command names can't be specified with absolute or relative paths.
     +o   The -p option of the built-in command command  can't  be
     +o   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
     getuid(2) and 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.,
     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
     and $HOME/.profile 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)  and  pdksh  was compiled with the DEFAULT_ENV macro defined,
 the file named in that macro 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.

   Command syntax    [Toc]    [Back]
     The  shells  begins  parsing  its  input by breaking it into
words.  Words,
     which are sequences of characters, are delimited by unquoted
     characters  (space,  tab,  and  newline)  or meta-characters
(`<', `>', `|',
     `;', `(', and `)').  Aside from delimiting words, spaces and
tabs are ignored,
  while  newlines usually delimit commands.  The metacharacters 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; `((
.. ))' is
     used in arithmetic expressions; and lastly, `( .. )' is used
to create

     Whitespace  and  meta-characters  can be quoted individually
using a backslash
 (`'), or in groups using double (`"') or single  (`'')
     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
     Substitution below); ``'  introduces  an  old-style  command
     (see  Substitution  below); `~' begins a directory expansion
(see Tilde
     expansion below); `{' and `}' delimit  csh(1)  style  alterations (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
     (see  Parameters  below),  input/output  redirections   (see
     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 0  is
there were no
     command substitutions.

     Commands can be chained together using the `|' token to form
     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
     status will be 1; if the original status was not 0, 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.  Note that  the  `&&'  and  `||'  operators  are
   For  example,  both  of  these commands will
print only "bar":

           false && echo foo || echo bar
           true || echo foo && echo bar

     The `&' token causes the preceding command  to  be  executed
     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 SIGINT and SIGQUIT ignored and with input redirected
     /dev/null (however,  redirections  specified  in  the  asynchronous command
     have  precedence).   The  `|&'  operator starts a co-process
which is a special
 kind of asynchronous process (see Co-processes  below).
Note that a
     command  must  follow  the `&&' and `||' operators, while it
need not follow
     `&', `|&', or `;'.  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
     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
     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
semicolon, a
     newline,  or  a  (syntactically correct) reserved word.  For

           { 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
             Note that { and } are reserved words, not meta-characters.

     case word in [[(] pattern [| pattern] ... ) list  ;;  ]  ...
             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
             within  a pattern must be quoted.  Both the word and
the patterns
             are subject to parameter,  command,  and  arithmetic
             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

     for name [in word ... term] do list done
             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.
term is either
 a newline or a `;'.

     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 nonconditional
 list is executed, the exit status is zero.

     select name [in word ... term] do list done
             The select statement provides an automatic method of
             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 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
reprinted without
             executing list.  When list completes, the enumerated
list is
             printed  if REPLY is NULL, the prompt is printed and
so on.  This
             process 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 pre-checked 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
             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

     [[ expression ]]
             Similar to the test and [ ... ] commands  (described
later), with
             the following exceptions:

                   +o    Field  splitting and file name generation
are not performed
 on arguments.

                   +o   The -a (AND) and -o (OR) operators are replaced with
                       `&&' and `||', respectively.

                   +o    Operators  (e.g.,  `-f',  `=', `!', etc.)
must be unquoted.

                   +o   The second operand of the `!=' and `=' expressions are
                       patterns (e.g., the comparison [[ foobar =
f*r ]] succeeds).

                   +o   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.

                   +o    The  single  argument form of test, which
tests if the
                       argument has a  non-zero  length,  is  not
valid; explicit
                       operators  must  always be used (e.g., instead of [ str ]
                       use [[ -n str ]]).

                   +o   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    [Toc]    [Back]
     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
     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
     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:  See POSIX mode below for a special rule regarding sequences of the
     form "...`...

   Aliases    [Toc]    [Back]
     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.,
     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'
           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
     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
     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.

   Substitution    [Toc]    [Back]
     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
  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

     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
     words; any characters from the set space, tab,  and  newline
that appear in
     the IFS characters are called ``IFS whitespace''.  Sequences
of one or
     more IFS whitespace characters, in combination with zero  or
one non-IFS
     whitespace  characters, delimit a field.  As a special case,
leading and
     trailing IFS whitespace is stripped  (i.e.,  no  leading  or
trailing empty
     field is created by it); leading or trailing non-IFS whitespace does create
 an empty field.

     Example: If IFS is set  to  ``<space>:'',  the  sequence  of
     ``<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 $(command)
     normal quoting rules are used when command is parsed; however, for the
     `command`  form,  a `' followed by any of `$', ``', 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 (note that $(< 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 should be fixed

     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    [Toc]    [Back]
     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 simplecommand, in
     which case the assignments are in effect only for the  duration of the
     command  (such  assignments are also exported, see below for
     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
     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 the 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

             If name is set and not NULL, it is substituted; otherwise, word
             is substituted.

             If name is set and not NULL,  word  is  substituted;
             nothing is substituted.

             If name is set and not NULL, it is substituted; otherwise, it is
             assigned word and the resulting  value  of  name  is

             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
     are performed on it; if word is not needed, it is not evaluated.

     The  following  forms  of parameter substitution can also be

             The number of positional parameters if name 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, and two of
them result
             in the longest match.

     ${name%pattern}, ${name%%pattern}
             Like  ${..#..} substitution, but it deletes from the
end of the

     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,

     $        The process ID of the shell,  or  the  PID  of  the
original shell if
              it  is  a  subshell.  Do NOT use this mechanism for
generating temporary
 file names; see mktemp(1) instead.

     -        The concatenation of the current single letter  options (see the
              set command below for a 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

     @        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
                ``.''  or contains an empty path, the current directory is not
                searched.  Also, the  cd  built-in  command  will
display the resulting
  directory  when  a match is found in any
search path
                other than the empty path.

     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 the select, set
-o, and kill
                -l commands to format information 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 startup
                file.  It typically contains function  and  alias

     ERRNO       Integer value of the shell's errno variable.  It
indicates the
                reason the last system call failed.  Not yet  implemented.

     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 command 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 to
                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.  The default
 is 128.

     HOME        The default directory for the cd command and the
value substituted
 for an unqualified ~ (see  Tilde  expansion

     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

                Note: This parameter is not imported from the environment when
                the shell is started.

                The version of the shell and the date the version
was created
                (read-only).  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 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 set to
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.

                If set, this parameter causes the posix option to
be enabled.
                See POSIX mode below.

     PPID       The process ID of the shell's parent (read-only).

     PS1         The  primary prompt for interactive shells.  Parameter, command,
 and arithmetic substitutions are performed,
and `!' is
                replaced with the current command number (see the
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  the  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
                characters,  you're  out  of  luck.   By the way,
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
                tracing (see the set -x command below).   Parameter, command,
                and arithmetic substitutions are performed before
it is printed.
  Default is ``+ ''.

     PWD        The current working directory.  May be  unset  or
NULL if the
                shell doesn't know where it is.

     RANDOM      A random number generator.  Every time RANDOM is
                it is assigned the  next  random  number  in  the
range 0-32767.
                By default, arc4random(3) is used to produce values.  If the
                variable RANDOM is assigned a value, the value is
used as seed
                to  srand(3)  and subsequent references of RANDOM
will use
                rand(3) to produce values, resulting  in  a  predictable sequence.

     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

     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
                ``emacs''  or  ``gmacs'',  the vi, emacs or gmacs
(Gosling emacs)
                editing mode is enabled, respectively.

   Tilde expansion    [Toc]    [Back]
     Tilde expansion, which is done in  parallel  with  parameter
     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
     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 reused.
  The alias -d command may be used to list, change, and
add to this
     cache   (e.g.,   alias   -d   fac=/usr/local/facilities;  cd

   Brace expansion (alteration)    [Toc]    [Back]
     Brace expressions, which take the form


     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
words: ``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.

   File name patterns    [Toc]    [Back]
     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 to 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

     [!..]    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'',
             ``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'',
``foobar'', 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

     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.

   Input/output redirection
     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

     >| file
             Same as >, except the file is truncated, even if the
             option is set.

     >> file
             Same  as  >, except if file exists it 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

     < file  Standard input is redirected  from  file,  which  is
opened for reading.

     <> file
             Same as <, except the file is opened for reading and

     << 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
             `0wline'.   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

     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 expanded 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.

   Arithmetic expressions    [Toc]    [Back]
     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.

     Expressions 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 operators:
           ?: (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 -

           !        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

           --       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 the value
                   of the expression on the right-hand side.

           =       Assignment; variable on the left is set to the
value on the

           *= /= += -= <<= >>= &= ^= |=
                   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) XOR (exclusive-OR).

           &       Arithmetic (bit-wise) AND.

           ==      Equal; the result is 1 if both  arguments  are
equal, 0 if

           !=       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>,

   Co-processes    [Toc]    [Back]
     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
     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's 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  coprocess has
     been redirected using an exec n<&p redirection.

     Some notes concerning co-processes:

     +o   The only way to close the co-process's input (so the coprocess 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>&-).

     +o   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 endof-file
 will not  be  detected  until  all  co-processes
sharing the coprocess's
  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-process output when the most recently started co-process (instead
         of when all sharing co-processes) exits.

     +o    print  -p  will ignore SIGPIPE signals during writes if
the signal is
         not being trapped or ignored; the same is  true  i

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