KSH(1) User commands KSH(1)
NAME
ksh - Public domain Korn shell
SYNOPSIS
ksh [+-abCefhikmnprsuvxX] [+-o option] [ [ -c command-string [command-
name] | -s | file ] [argument ...] ]
DESCRIPTION
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.
Shell Startup
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 base-
name 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:
o the cd command is disabled
o the SHELL, ENV and PATH parameters can't be changed
o command names can't be specified with absolute or relative paths
o the -p option of the command built-in can't be used
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 (see
getuid(2), getgid(2)). A privileged shell does not process $HOME/.pro-
file nor the ENV parameter (see below), instead the file /etc/suid_pro-
file 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/pro-
file, $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.
Command Syntax
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 cre-
ate asynchronous pipelines; && and || are used to specify conditional
execution; ;; is used in case statements; (( .. )) are used in arith-
metic expressions; and lastly, ( .. ) are used to create subshells.
White-space and meta-characters can be quoted individually using back-
slash (\), 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 men-
tioned quoting characters (see Quoting below); #, if used at the begin-
ning of a word, introduces a comment -- everything after the # up to
the nearest newline is ignored; $ is used to introduce parameter, com-
mand and arithmetic substitutions (see Substitution below); ` intro-
duces 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, group-
ing 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 argu-
ments. 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 sta-
tus of a pipeline is that of its last command. A pipeline may be pre-
fixed by the ! reserved word which causes the exit status of the pipe-
line 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 condi-
tional 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 com-
plete (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 redi-
rected, so any environment changes inside them may fail. To be porta-
ble, 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 exam-
ple,
{ 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 exe-
cuted 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 state-
ment 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 enumer-
ated 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 state-
ment 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 defini-
tion 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 com-
mand below.
[[ expression ]]
Similar to the test and [ ... ] commands (described later), with
the following exceptions:
o Field splitting and file name generation are not per-
formed 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 != and = expressions are patterns
(e.g., the comparison in
[[ 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, respec-
tively.
o 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 ]]
o Parameter, command and arithmetic substitutions are per-
formed 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
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 substitu-
tion) except no field splitting is carried out on the results of dou-
ble-quoted substitutions. If a \ inside a double-quoted string is fol-
lowed by \, $, ` or ", it is replaced by the second character; if it is
followed by a newline, both the \ and the newline are stripped; other-
wise, both the \ and the character following are unchanged.
Note: see POSIX Mode below for a special rule regarding sequences of
the form "...`...\"...`..".
Aliases
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., sub-
stitutes 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 com-
mand. 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.
Substitution
The first step the shell takes in executing a simple-command is to per-
form substitutions on the words of the command. There are three kinds
of substitution: parameter, command and arithmetic. Parameter substi-
tutions, 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 sub-
ject to brace expansion and file name expansion (see the relevant sec-
tions below).
A command substitution is replaced by the output generated by the spec-
ified command, which is run in a subshell. For $(command) substitu-
tions, 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 match-
ing 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
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 let-
ters 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 ele-
ment) 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 exam-
ple, `FOO=bar' sets the parameter FOO to bar; multiple parameter
assignments can be given on a single command line and they can be fol-
lowed 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 parame-
ters as well as the getopts, read and set -A commands. Lastly, parame-
ters can be assigned values using assignment operators inside arith-
metic 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 automati-
cally 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 condi-
tions only depend on name being set (as opposed to set and not null).
If word is needed, parameter, command, arithmetic and tilde substitu-
tion 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 back-
ground 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 com-
mand-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 func-
tion 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 sepa-
rate 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 parame-
ter 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 parame-
ter 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. Cur-
rently 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 invo-
cations of the shell running on the same machine will share his-
tory 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 his-
tory file.
HISTSIZE
The number of commands normally stored for history, default 128.
HOME The default directory for the cd command and the value substi-
tuted 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 (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 cur-
rently 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 sepa-
rated, and each file may be followed by a ? and a message to be
printed if new mail has arrived. Command, parameter and arith-
metic substitution is performed on the message, and, during sub-
stitution, the parameter $_ contains the name of the file. The
default message is you have mail in $_.
OLDPWD The previous working directory. Unset if cd has not success-
fully changed directories since the shell started, or if the
shell doesn't know where it is.
OPTARG When using getopts, it contains the argument for a parsed
option, if it requires one.
OPTIND The index of the last argument processed when using getopts.
Assigning 1 to this parameter causes getopts to process argu-
ments from the beginning the next time it is invoked.
PATH A colon separated list of directories that are searched when
looking for commands and .'d files. An empty string resulting
from a leading or trailing colon, or two adjacent colons is
treated as a `.', the current directory.
POSIXLY_CORRECT
If set, this parameter causes the posix option to be enabled.
See POSIX Mode below.
PPID The process ID of the shell's parent (readonly).
PS1 PS1 is the primary prompt for interactive shells. Parameter,
command and arithmetic substitutions are performed, and ! is
replaced with the current command number (see fc command below).
A literal ! can be put in the prompt by placing !! in PS1. Note
that since the command line editors try to figure out how long
the prompt is (so they know how far it is to edge of the
screen), escape codes in the prompt tend to mess things up. You
can tell the shell not to count certain sequences (such as
escape codes) by prefixing your prompt with a non-printing char-
acter (such as control-A) followed by a carriage return and then
delimiting the escape codes with this non-printing character.
If you don't have any non-printing characters, you're out of
luck... BTW, don't blame me for this hack; it's in the original
ksh. Default is `$ ' 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 trac-
ing (see set -x command below). Parameter, command and arith-
metic 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 refer-
enced, it is assigned the next number in a random number series.
The point in the series can be set by assigning a number to RAN-
DOM (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 parame-
ter 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 speci-
fies 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 spec-
ified in this parameter contains the string vi, emacs or gmacs,
the vi, emacs or gmacs (Gosling emacs) editing mode is enabled,
respectively.
Tilde Expansion
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 OLD-
PWD parameter is substituted, respectively. Otherwise, the password
file is searched for the login name, and the tilde expression is sub-
stituted 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 Expansion (alternation)
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 parame-
ter substitution and before file name generation.
File Name Patterns
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 repre-
sent itself it must be quoted or appear later in the list.
[!..] like [..], except it matches any character not inside the brack-
ets.
*(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 occur-
rences 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 pat-
terns. 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 [..] expres-
sion) 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 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 redirect-
ion (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 pro-
cessed 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 com-
mand 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 associ-
ated 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 redi-
rected (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 cre-
ated 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
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 assign-
ment to an integer parameter.
Expression may contain alpha-numeric parameter identifiers, array ref-
erences, 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 nota-
tion 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 incre-
mented value of the parameter, when used as a postfix
operator, the result is the original value of the parame-
ter.
-- 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>.
Co-Processes
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:
o 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>&-).
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 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 behav-
iour 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.
o 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
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 reg-
ular 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 speci-
fied in the FPATH parameter for a file with the same name as the func-
tion, which, if found is read and executed. If after executing the
file, the named function is found to be defined, the function is exe-
cuted, 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 exe-
cuted.
Since functions are executed in the current shell environment, parame-
ter 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 spe-
cial 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 differ-
ently in the following ways from functions defined with the () nota-
tion:
o the $0 parameter is set to the name of the function (Bourne-
style functions leave $0 untouched).
o parameter assignments preceding function calls are not kept in
the shell environment (executing Bourne-style functions will
keep assignments).
o 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:
o A separate trap/signal environment will be used during the exe-
cution 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.
o The EXIT trap, if set in a function, will be executed after the
function returns.
POSIX Mode
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 deter-
mined 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 con-
tains 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:
o \" inside double quoted `..` command substitutions: in posix
mode, the \" is interpreted when the command is interpreted; in
non-posix mode, the backslash is stripped before the command
substitution is interpreted. For example, echo "`echo \"hi\"`"
produces `"hi"' in posix mode, `hi' in non-posix mode. To avoid
problems, use the $(...) form of command substitution.
o 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.
o 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.
o 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).
o getopts: in posix mode, options must start with a -; in non-
posix mode, options can start with either - or +.
o 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, how-
ever it can be explicitly turned on later.
o set -: in posix mode, this does not clear the verbose or xtrace
options; in non-posix mode, it does.
o 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 $?' prints 0 in
posix mode, 1 in non-posix mode. This construct is used in most
shell scripts that use the old getopt(1) command.
o argument expansion of alias, export, readonly, and typeset com-
mands: in posix mode, normal argument expansion done; in non-
posix mode, field splitting, file globing, brace expansion and
(normal) tilde expansion are turned off, and assignment tilde
expansion is turned on.
o signal specification: in posix mode, signals can be specified as
digits only if signal numbers match POSIX values (i.e., HUP=1,
INT=2, QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15); in non-
posix mode, signals can be always digits.
o alias expansion: in posix mode, alias expansion is only carried
out when reading command words; in non-posix mode, alias expan-
sion is carried out on any word following an alias that ended in
a space. For example, the following for loop
alias a='for ' i='j'
a i in 1 2; do echo i=$i j=$j; done
uses parameter i in posix mode, j in non-posix mode.
o test: in posix mode, the expression "-t" (preceded by some num-
ber 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).
Command Execution
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 com-
mand below) some special commands are very special in that no field
splitting, file globing, brace expansion nor tilde expansion is per-
formed on arguments that look like assignments. Regular built-in com-
mands 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 con-
sidered special or regular:
POSIX special commands
. continue exit return trap
: eval export set unset
break exec readonly shift
Additional ksh special commands
builtin times typeset
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 with-
out 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 expan-
sion, 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 avail-
able on systems which support job control. See Job Control
below for more information.
bind [-m] [key[=editing-command] ...]
Set or view the current emacs command editing key bind-
ings/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 direc-
tory $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., redi-
rection 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 func-
tions, their names are simply printed, for aliases, a command
that defines them is printed, and for commands found by search-
ing 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 new-
line, 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 recog-
nized.
The options are provided for compatibility with BSD shell
scripts: -n suppresses the trailing newline, -e enables back-
slash 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 num-
bers. 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 speci-
fied 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 argu-
ments (or positional parameters, if no arguments are given) and
to check for legal options. optstring contains the option let-
ters 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 argu-
ment, 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 with-
out 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 infor-
mation 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 speci-
fied, 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 expres-
sions 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 new-
line.
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 logi-
cal 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 parame-
ters, 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 descrip-
tor n or the current co-process (see Co-Processes above for com-
ments 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 com-
mand 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 parame-
ter. Options can be changed using the +-o option syntax, where
option is the long name of an option, or using the +-letter syn-
tax, 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 mes-
sages 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 over-
write).
-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 || state-
ments.
-f noglob Do not expand file name pat-
terns.
-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 rec-
ognized 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 inter-
active).
-p privileged Set automatically if, when the
shell starts, the real uid or
gid does not match the effec-
tive 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 speci-
fied 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 param-
eter 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 exe-
cuted, preceded by the value
of PS4.
-X markdirs Mark directories with a trail-
ing / during file name genera-
tion.
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 Edit-
ing 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 differ-
ently.
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' directo-
ries (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, char-
acters 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 nor-
mally 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 fol-
lowing 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 argu-
ment is a binary operator, then the binary operation is per-
formed (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 speci-
fied signals are received. Handler is either a null string,
indicating the signals are to be ignored, a minus (-), indicat-
ing that the default action is to be taken for the signals (see
signal(3)), or a string containing shell commands to be evalu-
ated and executed at the first opportunity (i.e., when the cur-
rent 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 han-
dlers are executed in the environment of the last executed com-
mand. 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 com-
mands; 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 parame-
ters 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 func-
tions. 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 cur-
rent width of a parameter (or the width of
its first assigned value) is used. Trailing
white space are stripped. If necessary, val-
ues 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 spec-
ified, 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 charac-
ters 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 compatibil-
ity).
-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 charac-
ters 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 imple-
mented yet.
ulimit<