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 com-
mand-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 avail-
able), ignores the INT, QUIT and TERM signals, and prints
prompts before reading input (see PS1 and PS2 parameters).
For non-interactive shells, the trackall option is on by
default (see set command below).
A shell is restricted if the -r option is used or if
either the basename of the name the shell is invoked with
or the SHELL parameter match the pattern *r*sh (e.g., rsh,
rksh, rpdksh, etc.). The following restrictions come into
effect after the shell processes any profile and $ENV
files:
+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 privi-
leged shell does not process $HOME/.profile nor the ENV
parameter (see below), instead the file /etc/suid_profile
is processed. Clearing the privileged option causes the
shell to set its effective user-id (group-id) to its real
user-id (group-id).
If the basename of the name the shell is called with
(i.e., argv[0]) starts with - or if the -l option is used,
the shell is assumed to be a login shell and the shell
reads and executes the contents of /etc/profile 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 pro-
cessed), its value is subjected to parameter, command,
arithmetic and tilde substitution and the resulting file
(if any) is read and executed. If 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
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-charac-
ters 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-Pro-
cesses below); ; is used to separate commands; & is used
to create asynchronous pipelines; && and || are used to
specify conditional execution; ;; is used in case state-
ments; (( .. )) are used in arithmetic expressions; and
lastly, ( .. ) are used to create subshells.
White-space and meta-characters can be quoted individually
using backslash (\), or in groups using double (") or sin-
gle (') quotes. Note that the following characters are
also treated specially by the shell and must be quoted if
they are to represent themselves: \, ", ', #, $, `, ~, {,
}, *, ? and [. The first three of these are the above
mentioned quoting characters (see Quoting below); #, if
used at the beginning of a word, introduces a comment --
everything after the # up to the nearest newline is
ignored; $ is used to introduce parameter, command and
arithmetic substitutions (see Substitution below); `
introduces an old-style command substitution (see Substi-
tution below); ~ begins a directory expansion (see Tilde
Expansion below); { and } delimit csh(1) style alterna-
tions (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, typi-
cally programs that are executed, and compound-commands,
such as for and if statements, grouping constructs and
function definitions.
A simple-command consists of some combination of parameter
assignments (see Parameters below), input/output redirec-
tions (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 exe-
cutable file that is located using the PATH parameter (see
Command Execution below). Note that all command con-
structs have an exit status: for external commands, this
is related to the status returned by wait(2) (if the com-
mand 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 sub-
stitution performed during the parameter assignment or
zero if there were no command substitutions.
Commands can be chained together using the | token to form
pipelines, in which the standard output of each command
but the last is piped (see pipe(2)) to the standard input
of the following command. The exit status of a pipeline
is that of its last command. A pipeline may be prefixed
by the ! reserved word which causes the exit status of the
pipeline to be logically complemented: if the original
status was 0 the complemented status will be 1, and if the
original status was not 0, then the complemented status
will be 0.
Lists of commands can be created by separating pipelines
by any of the following tokens: &&, ||, &, |& and ;. The
first two are for conditional execution: cmd1 && cmd2 exe-
cutes 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 com-
mand to be executed asynchronously, that is, the shell
starts the command, but does not wait for it to complete
(the shell does keep track of the status of asynchronous
commands -- see Job Control below). When an asynchronous
command is started when job control is disabled (i.e., in
most scripts), the command is started with signals INT and
QUIT ignored and with input redirected from /dev/null
(however, redirections specified in the asynchronous com-
mand have precedence). The |& operator starts a co-pro-
cess 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 com-
mand 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 com-
mand (i.e., they can't be preceded by parameter assign-
ments or redirections):
case else function then !
do esac if time [[
done fi in until {
elif for select while }
Note: Some shells (but not this one) execute control
structure commands in a subshell when one or more of their
file descriptors are redirected, so any environment
changes inside them may fail. To be portable, the exec
statement should be used instead to redirect file descrip-
tors 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 (syntac-
tically correct) reserved word. For example,
{ echo foo; echo bar; }
{ echo foo; echo bar<<newline>>}
{ { echo foo; echo bar; } }
are all valid, but
{ echo foo; echo bar }
is not.
( list )
Execute list in a subshell. There is no implicit
way to pass environment changes from a subshell
back to its parent.
{ list }
Compound construct; list is executed, but not in a
subshell. Note that { and } are reserved words,
not meta-characters.
case word in [ [(] pattern [| pattern] ... ) list ;; ] ...
esac
The case statement attempts to match word against
the specified patterns; the list associated with
the first successfully matched pattern is executed.
Patterns used in case statements are the same as
those used for file name patterns except that the
restrictions regarding . and / are dropped. Note
that any unquoted space before and after a pattern
is stripped; any space with a pattern must be
quoted. Both the word and the patterns are subject
to parameter, command, and arithmetic substitution
as well as tilde substitution. For historical rea-
sons, 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 exe-
cuted, 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 follow-
ing the elif, if any, is executed with similar con-
sequences. 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 sta-
tus of an if statement is that of non-conditional
list that is executed; if no non-conditional list
is executed, the exit status is zero.
select name [ in word ... term ] do list done
where term is either a newline or a ;. The select
statement provides an automatic method of present-
ing 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, nor-
mally `#? '). A number corresponding to one of the
enumerated words is then read from standard input,
name is set to the selected word (or is unset if
the selection is not valid), REPLY is set to what
was read (leading/trailing space is stripped), and
list is executed. If a blank line (i.e., zero or
more IFS characters) is entered, the menu is re-
printed without executing list. When list com-
pletes, the enumerated list is printed if REPLY is
null, the prompt is printed and so on. This pro-
cess is continues until an end-of-file is read, an
interrupt is received or a break statement is exe-
cuted 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 exe-
cuted only while the exit status of the first list
is non-zero.
while list do list done
A while is a prechecked loop. Its body is executed
as often as the exit status of the first list is
zero. The exit status of a while statement is the
last exit status of the list in the body of the
loop; if the body is not executed, the exit status
is zero.
function name { list }
Defines the function name. See Functions below.
Note that redirections specified after a function
definition are performed whenever the function is
executed, not when the function definition is exe-
cuted.
name () command
Mostly the same as function. See Functions below.
(( expression ))
The arithmetic expression expression is evaluated;
equivalent to let "expression". See Arithmetic
Expressions and the let command below.
[[ expression ]]
Similar to the test and [ ... ] commands (described
later), with the following exceptions:
+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 != 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 be
always be used, e.g., instead of
[ str ]
use
[[ -n str ]]
+o Parameter, command and arithmetic substitu-
tions are performed as expressions are eval-
uated 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 charac-
ters or words specially. There are three methods of quot-
ing: First, \ quotes the following character, unless it is
at the end of a line, in which case both the \ and the
newline are stripped. Second, a single quote (') quotes
everything up to the next single quote (this may span
lines). Third, a double quote (") quotes all characters,
except $, ` and \, up to the next unquoted double quote.
$ and ` inside double quotes have their usual meaning
(i.e., parameter, command or arithmetic substitution)
except no field splitting is carried out on the results of
double-quoted substitutions. If a \ inside a double-
quoted string is followed by \, $, ` or ", it is replaced
by the second character; if it is followed by a newline,
both the \ and the newline are stripped; otherwise, both
the \ and the character following are unchanged.
Note: 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., substitutes the alias name
for its value) when it reads the first word of a command.
An expanded alias is re-processed to check for more
aliases. If a command alias ends in a space or tab, the
following word is also checked for alias expansion. The
alias expansion process stops when a word that is not an
alias is found, when a quoted word is found or when an
alias word that is currently being expanded is found.
The following command aliases are defined automatically by
the shell:
autoload='typeset -fu'
functions='typeset -f'
hash='alias -t'
history='fc -l'
integer='typeset -i'
local='typeset'
login='exec login'
newgrp='exec newgrp'
nohup='nohup '
r='fc -e -'
stop='kill -STOP'
suspend='kill -STOP $$'
type='whence -v'
Tracked aliases allow the shell to remember where it found
a particular command. The first time the shell does a
path search for a command that is marked as a tracked
alias, it saves the full path of the command. The next
time the command is executed, the shell checks the saved
path to see that it is still valid, and if so, avoids
repeating the path search. Tracked aliases can be listed
and created using alias -t. Note that changing the PATH
parameter clears the saved paths for all tracked aliases.
If the trackall option is set (i.e., set -o trackall or
set -h), the shell tracks all commands. This option is
set automatically for non-interactive shells. For inter-
active shells, only the following commands are automati-
cally 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-com-
mand is to perform substitutions on the words of the
command. There are three kinds of substitution: parame-
ter, command and arithmetic. Parameter substitutions,
which are described in detail in the next section, take
the form $name or ${...}; command substitutions take the
form $(command) or `command`; and arithmetic substitutions
take the form $((expression)).
If a substitution appears outside of double quotes, the
results of the substitution are generally subject to word
or field splitting according to the current value of the
IFS parameter. The IFS parameter specifies a list of
characters which are used to break a string up into sev-
eral 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' con-
tains four fields: `A', `B', `' and `D'. Note that if the
IFS parameter is set to the null string, no field split-
ting is done; if the parameter is unset, the default value
of space, tab and newline is used.
The results of substitution are, unless otherwise speci-
fied, also subject to brace expansion and file name expan-
sion (see the relevant sections below).
A command substitution is replaced by the output generated
by the specified command, which is run in a subshell. For
$(command) substitutions, normal quoting rules are used
when command is parsed, however, for the `command` form, a
\ followed by any of $, ` or \ is stripped (a \ followed
by any other character is unchanged). As a special case
in command substitutions, a command of the form << file is
interpreted to mean substitute the contents of file ($(<
foo) has the same effect as $(cat foo), but it is carried
out more efficiently because no process is started).
NOTE: $(command) expressions are currently parsed by find-
ing the matching parenthesis, regardless of quoting. This
will hopefully be fixed soon.
Arithmetic substitutions are replaced by the value of the
specified expression. For example, the command echo
$((2+3*4)) prints 14. See Arithmetic Expressions for a
description of an expression.
Parameters
Parameters are shell variables; they can be assigned val-
ues 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). Parameter sub-
stitutions take the form $name or ${name}, where name is a
parameter name. If substitution is performed on a parame-
ter 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 charac-
ter parameters are set. Second, parameters are imported
from the shell's environment at startup. Third, parame-
ters 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 followed by a simple-command, in
which case the assignments are in effect only for the
duration of the command (such assignments are also
exported, see below for implications of this). Note that
both the parameter name and the = must be unquoted for the
shell to recognize a parameter assignment. The fourth way
of setting a parameter is with the export, readonly and
typeset commands; see their descriptions in the Command
Execution section. Fifth, for and select loops set param-
eters as well as the getopts, read and set -A commands.
Lastly, parameters can be assigned values using assignment
operators inside arithmetic expressions (see Arithmetic
Expressions below) or using the ${name=value} form of
parameter substitution (see below).
Parameters with the export attribute (set using the export
or typeset -x commands, or by parameter assignments fol-
lowed by simple commands) are put in the environment (see
environ(5)) of commands run by the shell as name=value
pairs. The order in which parameters appear in the envi-
ronment of a command is unspecified. When the shell
starts up, it extracts parameters and their values from
its environment and automatically sets the export
attribute for those parameters.
Modifiers can be applied to the ${name} form of parameter
substitution:
${name:-word}
if name is set and not null, it is substituted,
otherwise word is substituted.
${name:+word}
if name is set and not null, word is substituted,
otherwise nothing is substituted.
${name:=word}
if name is set and not null, it is substituted,
otherwise it is assigned word and the resulting
value of name is substituted.
${name:?word}
if name is set and not null, it is substituted,
otherwise word is printed on standard error (pre-
ceded by name:) and an error occurs (normally caus-
ing termination of a shell script, function or
.-script). If word is omitted the string `parame-
ter 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, parame-
ter, command, arithmetic and tilde substitution are per-
formed on it; if word is not needed, it is not evaluated.
The following forms of parameter substitution can also be
used:
${#name}
The number of positional parameters if name is *, @
or is not specified, or the length of the string
value of parameter name.
${#name[*]}, ${#name[@]}
The number of elements in the array name.
${name#pattern}, ${name##pattern}
If pattern matches the beginning of the value of
parameter name, the matched text is deleted from
the result of substitution. A single # results in
the shortest match, two #'s results in the longest
match.
${name%pattern}, ${name%%pattern}
Like ${..#..} substitution, but it deletes from the
end of the value.
The following special parameters are implicitly set by the
shell and cannot be set directly using assignments:
! Process id of the last background process started.
If no background processes have been started, the
parameter is not set.
# The number of positional parameters (i.e., $1, $2,
etc.).
$ The process ID of the shell, or the PID of the
original shell if it is a subshell.
- The concatenation of the current single letter
options (see set command below for list of
options).
? The exit status of the last non-asynchronous com-
mand 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 sup-
plied, 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 sup-
plied to the shell, function or .-script. Further
positional parameters may be accessed using ${num-
ber}.
* 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 char-
acter 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 loosing null
arguments or splitting arguments with spaces).
The following parameters are set and/or used by the shell:
_ (underscore)
In interactive use, this parameter is set to the
last word of the previous command. When a command
is executed, this parameter is set to the full path
of the command and is placed in the command's envi-
ronment. 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 begin-
ning with / in cd commands. Note that if CDPATH is
set and does not contain . nor an empty path, the
current directory is not searched.
COLUMNS
Set to the number of columns on the terminal or
window. Currently set to the cols value as
reported by stty(1) if that value is non-zero.
This parameter is used by the interactive line
editing modes, and by select, set -o and kill -l
commands to format information in columns.
EDITOR If the VISUAL parameter is not set, this parameter
controls the command line editing mode for interac-
tive shells. See VISUAL parameter below for how
this works.
ENV If this parameter is found to be set after any pro-
file 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 informa-
tion.
HISTFILE
The name of the file used to store history. When
assigned to, history is loaded from the specified
file. Also, several invocations of the shell run-
ning on the same machine will share history if
their HISTFILE parameters all point at the same
file.
NOTE: if HISTFILE isn't set, no history file is
used. This is different from the original Korn
shell, which uses $HOME/.sh_history; in future,
pdksh may also use a default history file.
HISTSIZE
The number of commands normally stored for history,
default 128.
HOME The default directory for the cd command and the
value substituted for an unqualified ~ (see Tilde
Expansion below).
IFS Internal field separator, used during substitution
and by the read command, to split values into dis-
tinct arguments; normally set to space, tab and
newline. See Substitution above for details.
Note: this parameter is not imported from the envi-
ronment when the shell is started.
KSH_VERSION
The version of shell and the date the version was
created (readonly). See also the version commands
in Emacs Interactive Input Line Editing and Vi
Interactive Input Line Editing, below.
LINENO The line number of the function or shell script
that is currently being executed.
Not implemented yet.
LINES Set to the number of lines on the terminal or win-
dow.
Not implemented yet.
MAIL If set, the user will be informed of the arrival of
mail in the named file. This parameter is ignored
if the MAILPATH parameter is set.
MAILCHECK
How often, in seconds, the shell will check for
mail in the file(s) specified by MAIL or MAILPATH.
If 0, the shell checks before each prompt. The
default is 600 (10 minutes).
MAILPATH
A list of files to be checked for mail. The list
is colon separated, and each file may be followed
by a ? and a message to be printed if new mail has
arrived. Command, parameter and arithmetic substi-
tution is performed on the message, and, during
substitution, the parameter $_ contains the name of
the file. The default message is you have mail in
$_.
OLDPWD The previous working directory. Unset if cd has
not successfully changed directories since the
shell started, or if the shell doesn't know where
it is.
OPTARG When using getopts, it contains the argument for a
parsed option, if it requires one.
OPTIND The index of the last argument processed when using
getopts. Assigning 1 to this parameter causes
getopts to process arguments from the beginning the
next time it is invoked.
PATH A colon separated list of directories that are
searched when looking for commands and .'d files.
An empty string resulting from a leading or trail-
ing colon, or two adjacent colons is treated as a
`.', the current directory.
POSIXLY_CORRECT
If set, this parameter causes the posix option to
be enabled. See POSIX Mode below.
PPID The process ID of the shell's parent (readonly).
PS1 PS1 is the primary prompt for interactive shells.
Parameter, command and arithmetic substitutions are
performed, and ! is replaced with the current com-
mand number (see fc command below). A literal !
can be put in the prompt by placing !! in PS1.
Note that since the command line editors try to
figure out how long the prompt is (so they know how
far it is to edge of the screen), escape codes in
the prompt tend to mess things up. You can tell
the shell not to count certain sequences (such as
escape codes) by prefixing your prompt with a non-
printing character (such as control-A) followed by
a carriage return and then delimiting the escape
codes with this non-printing character. If you
don't have any non-printing characters, you're out
of luck... BTW, don't blame me for this hack; it's
in the original ksh. Default is `$ ' for non-root
users, `# ' for root..
PS2 Secondary prompt string, by default `>> ', used when
more input is needed to complete a command.
PS3 Prompt used by select statement when reading a menu
selection. Default is `#? '.
PS4 Used to prefix commands that are printed during
execution tracing (see set -x command below).
Parameter, command and arithmetic substitutions are
performed before it is printed. Default is `+ '.
PWD The current working directory. Maybe unset or null
if shell doesn't know where it is.
RANDOM A simple random number generator. Every time RAN-
DOM is referenced, it is assigned the next number
in a random number series. The point in the series
can be set by assigning a number to RANDOM (see
rand(3)).
REPLY Default parameter for the read command if no names
are given. Also used in select loops to store the
value that is read from standard input.
SECONDS
The number of seconds since the shell started or,
if the parameter has been assigned an integer
value, the number of seconds since the assignment
plus the value that was assigned.
TMOUT If set to a positive integer in an interactive
shell, it specifies the maximum number of seconds
the shell will wait for input after printing the
primary prompt (PS1). If the time is exceeded, the
shell exits.
TMPDIR The directory shell temporary files are created in.
If this parameter is not set, or does not contain
the absolute path of a writable directory, tempo-
rary files are created in /tmp.
VISUAL If set, this parameter controls the command line
editing mode for interactive shells. If the last
component of the path specified in this parameter
contains the string vi, emacs or gmacs, the vi,
emacs or gmacs (Gosling emacs) editing mode is
enabled, respectively.
Tilde Expansion
Tilde expansion, which is done in parallel with parameter
substitution, is done on words starting with an unquoted
~. The characters following the tilde, up to the first /,
if any, are assumed to be a login name. If the login name
is empty, + or -, the value of the HOME, PWD, or OLDPWD
parameter is substituted, respectively. Otherwise, the
password file is searched for the login name, and the
tilde expression is substituted with the user's home
directory. If the login name is not found in the password
file or if any quoting or parameter substitution occurs in
the login name, no substitution is performed.
In parameter assignments (those preceding a simple-command
or those occurring in the arguments of alias, export,
readonly, and typeset), tilde expansion is done after any
unquoted colon (:), and login names are also delimited by
colons.
The home directory of previously expanded login names are
cached and re-used. The alias -d command may be used to
list, change and add to this cache (e.g., `alias -d
fac=/usr/local/facilities; cd ~fac/bin').
Brace Expansion (alternation)
Brace expressions, which take the form
prefix{str1,...,strN}suffix
are expanded to N words, each of which is the concatena-
tion of prefix, stri and suffix (e.g., `a{c,b{X,Y},d}e'
expands to four word: ace, abXe, abYe, and ade). As noted
in the example, brace expressions can be nested and the
resulting words are not sorted. Brace expressions must
contain an unquoted comma (,) for expansion to occur
(i.e., {} and {foo} are not expanded). Brace expansion is
carried out after parameter substitution and before file
name generation.
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 mean-
ing:
? 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 brackets.
*(pattern| ... |pattern)
matches any string of characters that matches zero
or more occurances 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 occurances 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 pat-
tern ?(foo|bar) only matches the strings `', `foo'
and `bar'.
@(pattern| ... |pattern)
matches a string that matches one of the specified
patterns. Example: the pattern @(foo|bar) only
matches the strings `foo' and `bar'.
!(pattern| ... |pattern)
matches any string that does not match one of the
specified patterns. Examples: the pattern
!(foo|bar) matches all strings except `foo' and
`bar'; the pattern !(*) matches no strings; the
pattern !(?)* matches all strings (think about it).
Note that pdksh currently never matches . and .., but the
original ksh, Bourne sh and bash do, so this may have to
change (too bad).
Note that none of the above pattern elements match either
a period (.) at the start of a file name or a slash (/),
even if they are explicitly used in a [..] sequence; also,
the names . and .. are never matched, even by the pattern
.*.
If the markdirs option is set, any directories that result
from file name generation are marked with a trailing /.
The POSIX character classes (i.e., [:class-name:] inside a
[..] expression) are not yet implemented.
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 redirection (called a here document), the shell
copies lines from the command source into a tempo-
rary file until a line matching marker is read.
When the command is executed, standard input is
redirected from the temporary file. If marker con-
tains no quoted characters, the contents of the
temporary file are processed as if enclosed in dou-
ble quotes each time the command is executed, so
parameter, command and arithmetic substitutions are
performed, along with backslash (\) escapes for $,
`, \ and \newline. If multiple here documents are
used on the same command line, they are saved in
order.
<<<<- marker
same as <<<<, except leading tabs are stripped from
lines in the here document.
<<& fd standard input is duplicated from file descriptor
fd. fd can be a single digit, indicating the num-
ber 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 stan-
dard output.
In any of the above redirections, the file descriptor that
is redirected (i.e., standard input or standard output)
can be explicitly given by preceding the redirection with
a single digit. Parameter, command and arithmetic substi-
tutions, tilde substitutions and file name generation are
all performed on the file, marker and fd arguments of
redirections. Note however, that the results of any file
name generation are only used if a single file is matched;
if multiple files match, the word with the unexpanded file
name generation characters is used. Note that in
restricted shells, redirections which can create files
cannot be used.
For simple-commands, redirections may appear anywhere in
the command, for compound-commands (if statements, etc.),
any redirections must appear at the end. Redirections are
processed after pipelines are created and in the order
they are given, so
cat /foo/bar 2>>&1 >> /dev/null | cat -n
will print an error with a line number prepended to it.
Arithmetic Expressions
Integer arithmetic expressions can be used with the let
command, inside $((..)) expressions, inside array refer-
ences (e.g., name[expr]), as numeric arguments to the test
command, and as the value of an assignment to an integer
parameter.
Expression may contain alpha-numeric parameter identi-
fiers, array references, and integer constants and may be
combined with the following C operators (listed and
grouped in increasing order of precedence).
Unary operators:
+ - ! ~ ++ --
Binary operators:
,
= *= /= %= += -= <<<<= >>>>= &= ^= |=
||
&&
|
^
&
== !=
<< <<= >>= >>
<<<< >>>>
+ -
* / %
Ternary operator:
?: (precedence is immediately higher than assign-
ment)
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 com-
pleteness).
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 origi-
nal value of the parameter.
++ similar to ++, except the paramter is decre-
mented by 1.
, seperates two arithmetic expressions; the
left hand side is evaluated first, then the
right. The result is value of the expres-
sion 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 argu-
ment is non-zero, 0 if not. The right argu-
ment is evaluated only if the left argument
is zero.
&& logical and; the result is 1 if both argu-
ments are non-zero, 0 if not. The right
argument is evaluated only if the left argu-
ment 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 argu-
ment 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 unspeci-
fied 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-pro-
cess input has been redirected using an exec n>>&p redirec-
tion. 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 ini-
tial 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-pro-
cess 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-processs output when the most recently started
co-process (instead of when all sharing co-pro-
cesses) 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). Func-
tions are like .-scripts in that they are executed in the
current environment, however, unlike .-scripts, shell
arguments (i.e., positional parameters, $1, etc.) are
never visible inside them. When the shell is determining
the location of a command, functions are searched after
special built-in commands, and before regular and non-reg-
ular built-ins, and before the PATH is searched.
An existing function may be deleted using unset -f func-
tion-name. A list of functions can be obtained using
typeset +f and the function definitions can be listed
using typeset -f. autoload (which is an alias for typeset
-fu) may be used to create undefined functions; when an
undefined function is executed, the shell searches the
path specified in the FPATH parameter for a file with the
same name as the function, which, if found is read and
executed. If after executing the file, the named function
is found to be defined, the function is executed, other-
wise, the normal command search is continued (i.e., the
shell searches the regular built-in command table and
PATH). Note that if a command is not found using PATH, an
attempt is made to autoload a function using FPATH (this
is an undocumented feature of the original Korn shell).
Functions can have two attributes, trace and export, which
can be set with typeset -ft and typeset -fx, respectively.
When a traced function is executed, the shell's xtrace
option is turned on for the functions duration, otherwise
the xtrace option is turned off. The export attribute of
functions is currently not used. In the original Korn
shell, exported functions are visible to shell scripts
that are executed.
Since functions are executed in the current shell environ-
ment, parameter assignments made inside functions are
visible after the function completes. If this is not the
desired effect, the typeset command can be used inside a
function to create a local parameter. Note that special
parameters (e.g., $$, $!) can't be scoped in this way.
The exit status of a function is that of the last command
executed in the function. A function can be made to fin-
ish immediately using the return command; this may also be
used to explicitly specify the exit status.
Functions defined with the function reserved word are
treated differently in the following ways from functions
defined with the () notation:
+o the $0 parameter is set to the name of the function
(Bourne-style functions leave $0 untouched).
+o parameter assignments preceeding function calls are
not kept in the shell environment (executing
Bourne-style functions will keep assignments). In
the future, the following differences will also be
added:
+o A separate trap/signal environment will be used
during the execution of functions. This will mean
that traps set inside a function will not affect
the shell's traps and signals that are not ignored
in the shell (but may be trapped) will have their
default effect in a function.
+o The EXIT trap, if set in a function, will be exe-
cuted 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 determined by the
state of the posix option (set -o posix) -- if it is on,
the POSIX behaviour is followed, otherwise it is not. The
posix option is set automatically when the shell starts up
if the environment contains the POSIXLY_CORRECT parameter.
(The shell can also be compiled so that it is in POSIX
mode by default, however this is usually not desirable).
The following is a list of things that are affected by the
state of the posix option:
+o \" inside double quoted `..` command substitutions:
in posix mode, the \" is interpreted when the com-
mand is interpreted; in non-posix mode, the back-
slash 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 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,
however it can be explicitly turned on later.
+o set -: in posix mode, this does not clear the ver-
bose 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 substitu-
tions performed in generating the set command. For
example, `set -- `false`; echo $?' prints 0 in
posix mode, 1 in non-posix mode. This construct is
used in most shell scripts that use the old
getopt(1) command.
+o argument expansion of alias, export, readonly, and
typeset commands: in posix mode, normal argument
expansion done; in non-posix mode, field splitting,
file globing, brace expansion and (normal) tilde
expansion are turned off, and assignment tilde
expansion is turned on.
+o signal specification: in posix mode, signals can be
specified as digits only if signal numbers match
POSIX values (i.e., HUP=1, INT=2, QUIT=3, ABRT=6,
KILL=9, ALRM=14, and TERM=15); in non-posix mode,
signals can be always digits.
+o alias expansion: in posix mode, alias expansion is
only carried out when reading command words; in
non-posix mode, alias expansion is carried out on
any word following an alias that ended in a space.
For example, the following for loop
alias a='for ' i='j'
a i in 1 2; do echo i=$i j=$j; done
uses parameter i in posix mode, j in non-posix mode.
Command Execution
After evaluation of command line arguments, redirections
and parameter assignments, the type of command is deter-
mined: 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. Spe-
cial built-in commands differ from other commands in that
the PATH parameter is not used to find them, an error dur-
ing their execution can cause a non-interactive shell to
exit and parameter assignments that are specified before
the command are kept after the command completes. Just to
confuse things, if the posix option is turned off (see set
command below) some special commands are very special in
that no field splitting, file globing, brace expansion nor
tilde expansion is preformed on arguments that look like
assignments. Regular built-in commands are different only
in that the PATH parameter is not used to find them.
The original ksh and POSIX differ somewhat in which com-
mands are considered 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 com-
mands may be treated differently from the POSIX special
and regular commands.
Once the type of the command has been determined, any com-
mand 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 envi-
ronment. The file is searched for in the directo-
ries of PATH. If arguments are given, the posi-
tional parameters may be used to access them while
file is being executed. If no arguments are given,
the positional parameters are those of the environ-
ment the command is used in.
: [ ... ]
The null command. Exit status is set to zero.
alias [ -d | -t [-r] ] [-x] [name1[=value1] ...]
Without arguments, alias lists all aliases and
their values. For any name without a value, its
value is listed. Any name with a value defines an
alias (see Aliases above).
The -x option sets the export attribute of an
alias, or, if no names are given, lists the aliases
with the export attribute (exporting an alias cur-
rently has no affect).
The -t option indicates that tracked aliases are to
be listed/set (values specified on the command line
are ignored for tracked aliases). The -r option
indicates that all tracked aliases are to be reset.
The -d causes directory aliases, which are used in
tilde expansion, to be listed or set (see Tilde
Expansion above).
bg [job ...]
Resume the specified stopped job(s) in the back-
ground. If no jobs are specified, %+ is assumed.
This command is only available on systems which
support job control. See Job Control below for
more information.
bind [-m] [key[=editing-command] ...]
Set or view the current emacs command editing key
bindings/macros. See Emacs Interactive Input Line
Editing 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 the search path for the
directory containing dir. A null path means the
current directory. If dir is missing, the home
directory $HOME is used. If dir is -, the previous
working directory is used (see OLDPWD parameter).
If -L option (logical path) is used or if the phys-
ical option (see set command below) isn't set, ref-
erences 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 cur-
rent directory, and the shell attempts to change to
the new directory.
command [-pvV] cmd [arg1 ...]
If neither the -v nor -V options are given, cmd is
executed exactly as if the command had not been
specified, with two exceptions: first, cmd cannot
be a shell function, and second, special built-in
commands lose their specialness (i.e., redirection
and utility errors do not cause the shell to exit,
and command assignments are not permanent). If the
-p option is given, a default search path is used
instead of the current value of PATH (the actual
value of the default path is system dependent: on
POSIXish systems, it is the value returned by
getconf CS_PATH
).
If the -v option is given, instead of executing
cmd, information about what would be executed is
given (and the same is done for arg1 ...): for spe-
cial and regular built-in commands and functions,
their names are simply printed, for aliases, a com-
mand that defines them is printed, and for commands
found by searching the PATH parameter, the full
path of the command is printed. If no command is
be found, (i.e., the path search fails), nothing is
printed and command exits with a non-zero status.
The -V option is like the -v option, except it is
more verbose.
continue [levels]
continue jumps to the beginning of the levelth
inner most for, select, until, or while loop.
level defaults to 1.
echo [-neE] [arg ...]
Prints its arguments (separated by spaces) followed
by a newline, to standard out. The newline is sup-
pressed if any of the arguments contain the back-
slash 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 backslash interpretation (a no-op, since
this is normally done), and -E which 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).
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 specified by the
FCEDIT parameter (if this parameter is not set,
/bin/ed is used), and then executed by the shell.
fc [-e - | -s] [-g] [old=new] [prefix]
Re-execute the selected command (the previous com-
mand by default) after performing the optional sub-
stitution 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 con-
trol. See Job Control below for more information.
getopts optstring name [arg ...]
getopts is used by shell procedures to parse the
specified arguments (or positional parameters, if
no arguments are given) and to check for legal
options. optstring contains the option letters
that getopts is to recognize. If a letter is fol-
lowed by a colon, the option is expected to have an
argument. Arguments containing options must all
start with either a - or a +, options that do not
take arguments may be grouped in a single argument.
If an option takes an argument and the option char-
acter is not the last character of the argument it
is found in, the remainder of the argument is taken
to be the option's argument, otherwise, the next
argument is the option's argument.
Each time getopts is invoked, it places the next
option in the shell parameter name and the index of
the next argument to be processed in the shell
parameter OPTIND. If the option was introduced
with a +, the option placed in name is prefixed
with a +. When an option requires an argument,
getopts places it in the shell parameter OPTARG.
When an illegal option or a missing option argument
is encountered a question mark or a colon is placed
in name (indicating an illegal option or missing
argument, respectively) and OPTARG is set to the
option character that caused the problem. An error
message is also printed to standard error if opt-
string 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) 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 differ-
ent sets of arguments without resetting OPTIND may
lead to unexpected results.
hash [-r] [name ...]
Without arguments, any hashed executable command
pathnames are listed. The -r option causes all
hashed commands to be removed from the hash table.
Each name is searched as if it where a command name
and added to the hash table if it is an executable
command.
jobs [-lpn] [job ...]
Display information about the specified jobs; if no
jobs are specified, all jobs are displayed. The -n
option causes information to be displayed only for
jobs that have changed state since the last notifi-
cation. If the -l option is used, the process-id
of each process in a job is also listed. The -p
option causes only the process group of each job to
be printed. See Job Control below for the format
of job and the displayed job.
kill [-s signame | -signum | -signame ] { job | pid |
-pgrp } ...
Send the specified signal to the specified jobs,
process ids, or process groups. If no signal is
specified, the signal TERM is sent. If a job is
specified, the signal is sent to the job's process
group. See Job Control below for the format of
job.
kill -l [exit-status ...]
Print the name of the signal that killed a process
which exited with the specified exit-statuses. If
no arguments are specified, a list of all the sig-
nals, their numbers and a short description of them
are printed.
let [expression ...]
Each expression is evaluated, see Arithmetic
Expressions above. If all expressions are success-
fully evaluated, the exit status is 0 (1) if the
last expression evaluated to non-zero (zero). If
an error occurs during the parsing or evaluation of
an expression, the exit status is greater than 1.
Since expressions may need to be quoted, (( expr ))
is syntactic sugar for let "expr".
print [-nprsun | -R [-en]] [argument ...]
Print prints its arguments on the standard output,
separated by spaces, and terminated with a newline.
The -n option suppresses the newline. By default,
certain C escapes are translated. These include
\b, \f, \n, \r, \t, \v, and \0### (# is an octal
digit, of which there may be 0 to 3). \c is equiv-
alent to using the -n option. \ expansion may be
inhibited with the -r option. The -s option prints
to the history file instead of standard output, the
-u option prints to file descriptor n (n defaults
to 1 if omitted), and the -p option prints to the
co-process (see Co-Processes above).
The -R option is used to emulate, to some degree,
the BSD echo command, which does not process \
sequences unless the -e option is given. As above,
the -n option suppresses the trailing newline.
pwd [-LP]
Print the present working directory. If -L option
is used or if the physical option (see set command
below) isn't set, the logical path is printed
(i.e., the path used to cd to the current direc-
tory). If -P option (physical path) is used or if
the physical option is set, the path determined
from the filesystem (by following .. directories
to the root directory) is printed.
read [-prsun] [parameter ...]
Reads a line of input from standard input, separate
the line into fields using the IFS parameter (see
Substitution above), and assign each field to the
specified parameters. If there are more parameters
than fields, the extra parameters are set to null,
or alternatively, if there are more fields than
parameters, the last parameter is assigned the
remaining fields (inclusive of any separating
spaces). If no parameters are specified, the REPLY
parameter is used. If the input line ends in a
backslash and the -r option was not used, the back-
slash and newline are stripped and more input is
read. If no input is read, read exits with a non-
zero status.
The first parameter may have a question mark and a
string appended to it, in which case the string is
used as a prompt (printed to standard error before
any input is read) if the input is a tty (e.g.,
read nfoo?'number of foos: ').
The -un and -p options cause input to be read from
file descriptor n or the current co-process (see
Co-Processes above for comments on this), respec-
tively. If the -s option is used, input is saved
to the history file.
readonly [-p] [parameter[=value]] ...
Sets the readonly attribute of the named parame-
ters. If values are given, parameters are set to
them before setting the attribute. Once a parame-
ter 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 sta-
tus status. If no status is given, the exit status
of the last executed command is used. If used out-
side of a function or . script, it has the same
effect as exit. Note that pdksh treats both pro-
file and $ENV files as . scripts, while the origi-
nal Korn shell only treats profiles as . scripts.
set [+-abCefhkmnpsuvxX] [+-o [option]] [+-A name] [--]
[arg ...]
The set command can be used to set (-) or clear (+)
shell options, set the positional parameters, or
set an array parameter. Options can be changed
using the +-o option syntax, where option is the
long name of an option, or using the +-letter 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
o