NAME
pdksh - Public domain Korn shell
SYNOPSIS
pdksh [+-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
basename of the name the shell is invoked with or the SHELL parameter
match the pattern *r*sh (e.g., rsh, rksh, rpdksh, etc.). The following
restrictions come into effect after the shell processes any profile and
$ENV files:
· the cd command is disabled
· the SHELL, ENV and PATH parameters can’t be changed
· command names can’t be specified with absolute or relative paths
· the -p option of the command built-in can’t be used
· redirections that create files can’t be used (i.e., >, >|, >>,
<>)
A shell is privileged if the -p option is used or if the real user-id
or group-id does not match the effective user-id or group-id (see
getuid(2), getgid(2)). A privileged shell does not process
$HOME/.profile nor the ENV parameter (see below), instead the file
/etc/suid_profile is processed. Clearing the privileged option causes
the shell to set its effective user-id (group-id) to its real user-id
(group-id).
If the basename of the name the shell is called with (i.e., argv[0])
starts with - or if the -l option is used, the shell is assumed to be a
login shell and the shell reads and executes the contents of
/etc/profile and $HOME/.profile if they exist and are readable.
If the ENV parameter is set when the shell starts (or, in the case of
login shells, after any profiles are processed), its value is subjected
to parameter, command, arithmetic and tilde substitution and the
resulting file (if any) is read and executed. If 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-characters
are used in building the following tokens: <, <&, <<, >, >&, >>, etc.
are used to specify redirections (see Input/Output Redirection below);
| is used to create pipelines; |& is used to create co-processes (see
Co-Processes below); ; is used to separate commands; & is used to
create asynchronous pipelines; && and || are used to specify
conditional execution; ;; is used in case statements; (( .. )) are used
in arithmetic expressions; and lastly, ( .. ) are used to create
subshells.
White-space and meta-characters can be quoted individually using
backslash (\), or in groups using double (") or single (’) quotes.
Note that the following characters are also treated specially by the
shell and must be quoted if they are to represent themselves: \, ", ’,
#, $, ‘, ~, {, }, *, ? and [. The first three of these are the above
mentioned quoting characters (see Quoting below); #, if used at the
beginning of a word, introduces a comment — everything after the # up
to the nearest newline is ignored; $ is used to introduce parameter,
command and arithmetic substitutions (see Substitution below); ‘
introduces an old-style command substitution (see Substitution below);
~ begins a directory expansion (see Tilde Expansion below); { and }
delimit csh(1) style alternations (see Brace Expansion below); and,
finally, *, ? and [ are used in file name generation (see File Name
Patterns below).
As words and tokens are parsed, the shell builds commands, of which
there are two basic types: simple-commands, typically programs that are
executed, and compound-commands, such as for and if statements,
grouping constructs and function definitions.
A simple-command consists of some combination of parameter assignments
(see Parameters below), input/output redirections (see Input/Output
Redirections below), and command words; the only restriction is that
parameter assignments come before any command words. The command
words, if any, define the command that is to be executed and its
arguments. The command may be a shell built-in command, a function or
an external command, i.e., a separate executable file that is located
using the PATH parameter (see Command Execution below). Note that all
command constructs have an exit status: for external commands, this is
related to the status returned by wait(2) (if the command could not be
found, the exit status is 127, if it could not be executed, the exit
status is 126); the exit status of other command constructs (built-in
commands, functions, compound-commands, pipelines, lists, etc.) are all
well defined and are described where the construct is described. The
exit status of a command consisting only of parameter assignments is
that of the last command substitution performed during the parameter
assignment or zero if there were no command substitutions.
Commands can be chained together using the | token to form pipelines,
in which the standard output of each command but the last is piped (see
pipe(2)) to the standard input of the following command. The exit
status of a pipeline is that of its last command. A pipeline may be
prefixed by the ! reserved word which causes the exit status of the
pipeline to be logically complemented: if the original status was 0 the
complemented status will be 1, and if the original status was not 0,
then the complemented status will be 0.
Lists of commands can be created by separating pipelines by any of the
following tokens: &&, ||, &, |& and ;. The first two are for
conditional execution: cmd1 && cmd2 executes cmd2 only if the exit
status of cmd1 is zero; || is the opposite — cmd2 is executed only if
the exit status of cmd1 is non-zero. && and || have equal precedence
which is higher than that of &, |& and ;, which also have equal
precedence. The & token causes the preceding command to be executed
asynchronously, that is, the shell starts the command, but does not
wait for it to complete (the shell does keep track of the status of
asynchronous commands — see Job Control below). When an asynchronous
command is started when job control is disabled (i.e., in most
scripts), the command is started with signals INT and QUIT ignored and
with input redirected from /dev/null (however, redirections specified
in the asynchronous command have precedence). The |& operator starts a
co-process which is special kind of asynchronous process (see Co-
Processes below). Note that a command must follow the && and ||
operators, while a command need not follow &, |& and ;. The exit
status of a list is that of the last command executed, with the
exception of asynchronous lists, for which the exit status is 0.
Compound commands are created using the following reserved words —
these words are only recognized if they are unquoted and if they are
used as the first word of a command (i.e., they can’t be preceded by
parameter assignments or redirections):
case else function then !
do esac if time [[
done fi in until {
elif for select while }
Note: Some shells (but not this one) execute control structure commands
in a subshell when one or more of their file descriptors are
redirected, so any environment changes inside them may fail. To be
portable, the exec statement should be used instead to redirect file
descriptors before the control structure.
In the following compound command descriptions, command lists (denoted
as list) that are followed by reserved words must end with a semi-
colon, a newline or a (syntactically correct) reserved word. For
example,
{ echo foo; echo bar; }
{ echo foo; echo bar<newline>}
{ { echo foo; echo bar; } }
are all valid, but
{ echo foo; echo bar }
is not.
( list )
Execute list in a subshell. There is no implicit way to pass
environment changes from a subshell back to its parent.
{ list }
Compound construct; list is executed, but not in a subshell.
Note that { and } are reserved words, not meta-characters.
case word in [ [(] pattern [| pattern] ... ) list ;; ] ... esac
The case statement attempts to match word against the specified
patterns; the list associated with the first successfully
matched pattern is executed. Patterns used in case statements
are the same as those used for file name patterns except that
the restrictions regarding . and / are dropped. Note that any
unquoted space before and after a pattern is stripped; any space
with a pattern must be quoted. Both the word and the patterns
are subject to parameter, command, and arithmetic substitution
as well as tilde substitution. For historical reasons, open and
close braces may be used instead of in and esac (e.g., case $foo
{ *) echo bar; }). The exit status of a case statement is that
of the executed list; if no list is executed, the exit status is
zero.
for name [ in word ... term ] do list done
where term is either a newline or a ;. For each word in the
specified word list, the parameter name is set to the word and
list is executed. If in is not used to specify a word list, the
positional parameters ("$1", "$2", etc.) are used instead. For
historical reasons, open and close braces may be used instead of
do and done (e.g., for i; { echo $i; }). The exit status of a
for statement is the last exit status of list; if list is never
executed, the exit status is zero.
if list then list [elif list then list] ... [else list] fi
If the exit status of the first list is zero, the second list is
executed; otherwise the list following the elif, if any, is
executed with similar consequences. If all the lists following
the if and elifs fail (i.e., exit with non-zero status), the
list following the else is executed. The exit status of an if
statement is that of non-conditional list that is executed; if
no non-conditional list is executed, the exit status is zero.
select name [ in word ... term ] do list done
where term is either a newline or a ;. The select statement
provides an automatic method of presenting the user with a menu
and selecting from it. An enumerated list of the specified
words is printed on standard error, followed by a prompt (PS3,
normally ‘#? ’). A number corresponding to one of the
enumerated words is then read from standard input, name is set
to the selected word (or is unset if the selection is not
valid), REPLY is set to what was read (leading/trailing space is
stripped), and list is executed. If a blank line (i.e., zero or
more IFS characters) is entered, the menu is re-printed without
executing list. When list completes, the enumerated list is
printed if REPLY is null, the prompt is printed and so on. This
process is continues until an end-of-file is read, an interrupt
is received or a break statement is executed inside the loop.
If in word ... is omitted, the positional parameters are used
(i.e., "$1", "$2", etc.). For historical reasons, open and
close braces may be used instead of do and done (e.g., select i;
{ echo $i; }). The exit status of a select statement is zero if
a break statement is used to exit the loop, non-zero otherwise.
until list do list done
This works like while, except that the body is executed only
while the exit status of the first list is non-zero.
while list do list done
A while is a prechecked loop. Its body is executed as often as
the exit status of the first list is zero. The exit status of a
while statement is the last exit status of the list in the body
of the loop; if the body is not executed, the exit status is
zero.
function name { list }
Defines the function name. See Functions below. Note that
redirections specified after a function definition are performed
whenever the function is executed, not when the function
definition is executed.
name () command
Mostly the same as function. See Functions below. Whitespace
(space or tab) after name will be ignored most of the time.
time [ -p ] [ pipeline ]
The time reserved word is described in the Command Execution
section.
(( expression ))
The arithmetic expression expression is evaluated; equivalent to
let "expression". See Arithmetic Expressions and the let
command below.
[[ expression ]]
Similar to the test and [ ... ] commands (described later), with
the following exceptions:
· Field splitting and file name generation are not
performed on arguments.
· The -a (and) and -o (or) operators are replaced with &&
and ||, respectively.
· Operators (e.g., -f, =, !, etc.) must be unquoted.
· The second operand of != and = expressions are patterns
(e.g., the comparison in
[[ foobar = f*r ]]
succeeds).
· There are two additional binary operators: < and > which
return true if their first string operand is less than,
or greater than, their second string operand,
respectively.
· The single argument form of test, which tests if the
argument has non-zero length, is not valid - explicit
operators must be always be used, e.g., instead of
[ str ]
use
[[ -n str ]]
· Parameter, command and arithmetic substitutions are
performed as expressions are evaluated and lazy
expression evaluation is used for the && and ||
operators. This means that in the statement
[[ -r foo && $(< foo) = b*r ]]
the $(< foo) is evaluated if and only if the file foo
exists and is readable.
Quoting
Quoting is used to prevent the shell from treating characters or words
specially. There are three methods of quoting: First, \ quotes the
following character, unless it is at the end of a line, in which case
both the \ and the newline are stripped. Second, a single quote (’)
quotes everything up to the next single quote (this may span lines).
Third, a double quote (") quotes all characters, except $, ‘ and \, up
to the next unquoted double quote. $ and ‘ inside double quotes have
their usual meaning (i.e., parameter, command or arithmetic
substitution) except no field splitting is carried out on the results
of double-quoted substitutions. If a \ inside a double-quoted string
is followed by \, $, ‘ or ", it is replaced by the second character; if
it is followed by a newline, both the \ and the newline are stripped;
otherwise, both the \ and the character following are unchanged.
Note: 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 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
perform substitutions on the words of the command. There are three
kinds of substitution: parameter, command and arithmetic. Parameter
substitutions, which are described in detail in the next section, take
the form $name or ${...}; command substitutions take the form
$(command) or ‘command‘; and arithmetic substitutions take the form
$((expression)).
If a substitution appears outside of double quotes, the results of the
substitution are generally subject to word or field splitting according
to the current value of the IFS parameter. The IFS parameter specifies
a list of characters which are used to break a string up into several
words; any characters from the set space, tab and newline that appear
in the IFS characters are called IFS white space. Sequences of one or
more IFS white space characters, in combination with zero or one non-
IFS white space characters delimit a field. As a special case, leading
and trailing IFS white space is stripped (i.e., no leading or trailing
empty field is created by it); leading or trailing non-IFS white space
does create an empty field. Example: if IFS is set to ‘<space>:’, the
sequence of characters ‘<space>A<space>:<space><space>B::D’ contains
four fields: ‘A’, ‘B’, ‘’ and ‘D’. Note that if the IFS parameter is
set to the null string, no field splitting is done; if the parameter is
unset, the default value of space, tab and newline is used.
The results of substitution are, unless otherwise specified, also
subject to brace expansion and file name expansion (see the relevant
sections below).
A command substitution is replaced by the output generated by the
specified command, which is run in a subshell. For $(command)
substitutions, normal quoting rules are used when command is parsed,
however, for the ‘command‘ form, a \ followed by any of $, ‘ or \ is
stripped (a \ followed by any other character is unchanged). As a
special case in command substitutions, a command of the form < file is
interpreted to mean substitute the contents of file ($(< foo) has the
same effect as $(cat foo), but it is carried out more efficiently
because no process is started).
NOTE: $(command) expressions are currently parsed by finding the
matching parenthesis, regardless of quoting. This will hopefully be
fixed soon.
Arithmetic substitutions are replaced by the value of the specified
expression. For example, the command echo $((2+3*4)) prints 14. See
Arithmetic Expressions for a description of an expression.
Parameters
Parameters are shell variables; they can be assigned values and their
values can be accessed using a parameter substitution. A parameter
name is either one of the special single punctuation or digit character
parameters described below, or a letter followed by zero or more
letters or digits (‘_’ counts as a letter). The later form can be
treated as arrays by appending an array index of the form: [expr] where
expr is an arithmetic expression. Array indices are currently limited
to the range 0 through 1023, inclusive. Parameter substitutions take
the form $name, ${name} or ${name[expr]}, where name is a parameter
name. If substitution is performed on a parameter (or an array
parameter element) that is not set, a null string is substituted unless
the nounset option (set -o nounset or set -u) is set, in which case an
error occurs.
Parameters can be assigned values in a number of ways. First, the
shell implicitly sets some parameters like #, PWD, etc.; this is the
only way the special single character parameters are set. Second,
parameters are imported from the shell’s environment at startup.
Third, parameters can be assigned values on the command line, for
example, ‘FOO=bar’ sets the parameter FOO to bar; multiple parameter
assignments can be given on a single command line and they can be
followed by a simple-command, in which case the assignments are in
effect only for the duration of the command (such assignments are also
exported, see below for implications of this). Note that both the
parameter name and the = must be unquoted for the shell to recognize a
parameter assignment. The fourth way of setting a parameter is with
the export, readonly and typeset commands; see their descriptions in
the Command Execution section. Fifth, for and select loops set
parameters as well as the getopts, read and set -A commands. Lastly,
parameters can be assigned values using assignment operators inside
arithmetic expressions (see Arithmetic Expressions below) or using the
${name=value} form of parameter substitution (see below).
Parameters with the export attribute (set using the export or typeset
-x commands, or by parameter assignments followed by simple commands)
are put in the environment (see environ(7)) of commands run by the
shell as name=value pairs. The order in which parameters appear in the
environment of a command is unspecified. When the shell starts up, it
extracts parameters and their values from its environment and
automatically sets the export attribute for those parameters.
Modifiers can be applied to the ${name} form of parameter substitution:
${name:-word}
if name is set and not null, it is substituted, otherwise word
is substituted.
${name:+word}
if name is set and not null, word is substituted, otherwise
nothing is substituted.
${name:=word}
if name is set and not null, it is substituted, otherwise it is
assigned word and the resulting value of name is substituted.
${name:?word}
if name is set and not null, it is substituted, otherwise word
is printed on standard error (preceded by name:) and an error
occurs (normally causing termination of a shell script, function
or .-script). If word is omitted the string ‘parameter null or
not set’ is used instead.
In the above modifiers, the : can be omitted, in which case the
conditions only depend on name being set (as opposed to set and not
null). If word is needed, parameter, command, arithmetic and tilde
substitution are performed on it; if word is not needed, it is not
evaluated.
The following forms of parameter substitution can also be used:
${#name}
The number of positional parameters if name is *, @ or is not
specified, or the length of the string value of parameter name.
${#name[*]}, ${#name[@]}
The number of elements in the array name.
${name#pattern}, ${name##pattern}
If pattern matches the beginning of the value of parameter name,
the matched text is deleted from the result of substitution. A
single # results in the shortest match, two #’s results in the
longest match.
${name%pattern}, ${name%%pattern}
Like ${..#..} substitution, but it deletes from the end of the
value.
The following special parameters are implicitly set by the shell and
cannot be set directly using assignments:
! Process id of the last background process started. If no
background processes have been started, the parameter is not
set.
# The number of positional parameters (i.e., $1, $2, etc.).
$ The process ID of the shell, or the PID of the original shell if
it is a subshell.
- The concatenation of the current single letter options (see set
command below for list of options).
? The exit status of the last non-asynchronous command executed.
If the last command was killed by a signal, $? is set to 128
plus the signal number.
0 The name the shell was invoked with (i.e., argv[0]), or the
command-name if it was invoked with the -c option and the
command-name was supplied, or the file argument, if it was
supplied. If the posix option is not set, $0 is the name of the
current function or script.
1 ... 9
The first nine positional parameters that were supplied to the
shell, function or .-script. Further positional parameters may
be accessed using ${number}.
* All positional parameters (except parameter 0), i.e., $1 $2
$3.... If used outside of double quotes, parameters are
separate words (which are subjected to word splitting); if used
within double quotes, parameters are separated by the first
character of the IFS parameter (or the empty string if IFS is
null).
@ Same as $*, unless it is used inside double quotes, in which
case a separate word is generated for each positional parameter
- if there are no positional parameters, no word is generated
("$@" can be used to access arguments, verbatim, without loosing
null arguments or splitting arguments with spaces).
The following parameters are set and/or used by the shell:
_ (underscore)
When an external command is executed by the shell, this
parameter is set in the environment of the new process to the
path of the executed command. In interactive use, this
parameter is also set in the parent shell to the last word of
the previous command. When MAILPATH messages are evaluated,
this parameter contains the name of the file that changed (see
MAILPATH parameter below).
CDPATH Search path for the cd built-in command. Works the same way as
PATH for those directories not beginning with / in cd commands.
Note that if CDPATH is set and does not contain . nor an empty
path, the current directory is not searched.
COLUMNS
Set to the number of columns on the terminal or window.
Currently set to the cols value as reported by stty(1) if that
value is non-zero. This parameter is used by the interactive
line editing modes, and by select, set -o and kill -l commands
to format information in columns.
EDITMODE
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.
EDITOR If the VISUAL parameter is not set, this parameter controls the
command line editing mode for interactive shells. See EDITMODE
parameter above for how this works.
ENV If this parameter is found to be set after any profile files are
executed, the expanded value is used as a shell start-up file.
It typically contains function and alias definitions.
ERRNO Integer value of the shell’s errno variable — indicates the
reason the last system call failed.
Not implemented yet.
EXECSHELL
If set, this parameter is assumed to contain the shell that is
to be used to execute commands that execve(2) fails to execute
and which do not start with a ‘#! shell’ sequence.
FCEDIT The editor used by the fc command (see below).
FPATH Like PATH, but used when an undefined function is executed to
locate the file defining the function. It is also searched when
a command can’t be found using PATH. See Functions below for
more information.
HISTFILE
The name of the file used to store history. When assigned to,
history is loaded from the specified file. Also, several
invocations of the shell running on the same machine will share
history if their HISTFILE parameters all point at the same file.
NOTE: if HISTFILE isn’t set, no history file is used. This is
different from the original Korn shell, which uses
$HOME/.sh_history; in future, pdksh may also use a default
history file.
HISTSIZE
The number of commands normally stored for history, default 128.
HOME The default directory for the cd command and the value
substituted for an unqualified ~ (see Tilde Expansion below).
IFS Internal field separator, used during substitution and by the
read command, to split values into distinct arguments; normally
set to space, tab and newline. See Substitution above for
details.
Note: this parameter is not imported from the environment when
the shell is started.
KSH_VERSION
The version of shell and the date the version was created
(readonly). See also the version commands in Emacs Editing Mode
and Vi Editing Mode sections, below.
LINENO The line number of the function or shell script that is
currently being executed.
LINES Set to the number of lines on the terminal or window.
Not implemented yet.
MAIL If set, the user will be informed of the arrival of mail in the
named file. This parameter is ignored if the MAILPATH parameter
is set.
MAILCHECK
How often, in seconds, the shell will check for mail in the
file(s) specified by MAIL or MAILPATH. If 0, the shell checks
before each prompt. The default is 600 (10 minutes).
MAILPATH
A list of files to be checked for mail. The list is colon
separated, and each file may be followed by a ? and a message to
be printed if new mail has arrived. Command, parameter and
arithmetic substitution is performed on the message, and, during
substitution, the parameter $_ contains the name of the file.
The default message is you have mail in $_.
OLDPWD The previous working directory. Unset if cd has not
successfully changed directories since the shell started, or if
the shell doesn’t know where it is.
OPTARG When using getopts, it contains the argument for a parsed
option, if it requires one.
OPTIND The index of the last argument processed when using getopts.
Assigning 1 to this parameter causes getopts to process
arguments from the beginning the next time it is invoked.
PATH A colon separated list of directories that are searched when
looking for commands and .’d files. An empty string resulting
from a leading or trailing colon, or two adjacent colons is
treated as a ‘.’, the current directory.
POSIXLY_CORRECT
If set, this parameter causes the posix option to be enabled.
See POSIX Mode below.
PPID The process ID of the shell’s parent (readonly).
PS1 PS1 is the primary prompt for interactive shells. Parameter,
command and arithmetic substitutions are performed, and ! is
replaced with the current command number (see fc command below).
A literal ! can be put in the prompt by placing !! in PS1. Note
that since the command line editors try to figure out how long
the prompt is (so they know how far it is to edge of the
screen), escape codes in the prompt tend to mess things up. You
can tell the shell not to count certain sequences (such as
escape codes) by prefixing your prompt with a non-printing
character (such as control-A) followed by a carriage return and
then delimiting the escape codes with this non-printing
character. If you don’t have any non-printing characters,
you’re out of luck... BTW, don’t blame me for this hack; it’s
in the original ksh. Default is ‘$ ’ for non-root users, ‘# ’
for root..
PS2 Secondary prompt string, by default ‘> ’, used when more input
is needed to complete a command.
PS3 Prompt used by select statement when reading a menu selection.
Default is ‘#? ’.
PS4 Used to prefix commands that are printed during execution
tracing (see set -x command below). Parameter, command and
arithmetic substitutions are performed before it is printed.
Default is ‘+ ’.
PWD The current working directory. Maybe unset or null if shell
doesn’t know where it is.
RANDOM A simple random number generator. Every time RANDOM is
referenced, it is assigned the next number in a random number
series. The point in the series can be set by assigning a
number to RANDOM (see rand(3)).
REPLY Default parameter for the read command if no names are given.
Also used in select loops to store the value that is read from
standard input.
SECONDS
The number of seconds since the shell started or, if the
parameter has been assigned an integer value, the number of
seconds since the assignment plus the value that was assigned.
TMOUT If set to a positive integer in an interactive shell, it
specifies the maximum number of seconds the shell will wait for
input after printing the primary prompt (PS1). If the time is
exceeded, the shell exits.
TMPDIR The directory shell temporary files are created in. If this
parameter is not set, or does not contain the absolute path of a
writable directory, temporary files are created in /tmp.
VISUAL If set, and EDITMODE is unset, 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 concatenation of prefix,
stri and suffix (e.g., ‘a{c,b{X,Y},d}e’ expands to four word: ace,
abXe, abYe, and ade). As noted in the example, brace expressions can
be nested and the resulting words are not sorted. Brace expressions
must contain an unquoted comma (,) for expansion to occur (i.e., {} and
{foo} are not expanded). Brace expansion is carried out after
parameter substitution and before file name generation.
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
represent itself it must be quoted or appear later in the list.
[!..] like [..], except it matches any character not inside the
brackets.
*(pattern| ... |pattern)
matches any string of characters that matches zero or more
occurrences of the specified patterns. Example: the pattern
*(foo|bar) matches the strings ‘’, ‘foo’, ‘bar’, ‘foobarfoo’,
etc..
+(pattern| ... |pattern)
matches any string of characters that matches one or more
occurrences of the specified patterns. Example: the pattern
+(foo|bar) matches the strings ‘foo’, ‘bar’, ‘foobarfoo’, etc..
?(pattern| ... |pattern)
matches the empty string or a string that matches one of the
specified patterns. Example: the pattern ?(foo|bar) only
matches the strings ‘’, ‘foo’ and ‘bar’.
@(pattern| ... |pattern)
matches a string that matches one of the specified patterns.
Example: the pattern @(foo|bar) only matches the strings ‘foo’
and ‘bar’.
!(pattern| ... |pattern)
matches any string that does not match one of the specified
patterns. Examples: the pattern !(foo|bar) matches all strings
except ‘foo’ and ‘bar’; the pattern !(*) matches no strings; the
pattern !(?)* matches all strings (think about it).
Note that pdksh currently never matches . and .., but the original ksh,
Bourne sh and bash do, so this may have to change (too bad).
Note that none of the above pattern elements match either a period (.)
at the start of a file name or a slash (/), even if they are explicitly
used in a [..] sequence; also, the names . and .. are never matched,
even by the pattern .*.
If the markdirs option is set, any directories that result from file
name generation are marked with a trailing /.
The POSIX character classes (i.e., [:class-name:] inside a [..]
expression) are not yet implemented.
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 temporary file until a line
matching marker is read. When the command is executed, standard
input is redirected from the temporary file. If marker contains
no quoted characters, the contents of the temporary file are
processed as if enclosed in double quotes each time the command
is executed, so parameter, command and arithmetic substitutions
are performed, along with backslash (\) escapes for $, ‘, \ and
\newline. If multiple here documents are used on the same
command line, they are saved in order.
<<- marker
same as <<, except leading tabs are stripped from lines in the
here document.
<& fd standard input is duplicated from file descriptor fd. fd can be
a single digit, indicating the number of an existing file
descriptor, the letter p, indicating the file descriptor
associated with the output of the current co-process, or the
character -, indicating standard input is to be closed.
>& fd same as <&, except the operation is done on standard output.
In any of the above redirections, the file descriptor that is
redirected (i.e., standard input or standard output) can be explicitly
given by preceding the redirection with a single digit. Parameter,
command and arithmetic substitutions, tilde substitutions and (if the
shell is interactive) file name generation are all performed on the
file, marker and fd arguments of redirections. Note however, that the
results of any file name generation are only used if a single file is
matched; if multiple files match, the word with the unexpanded file
name generation characters is used. Note that in restricted shells,
redirections which can create files cannot be used.
For simple-commands, redirections may appear anywhere in the command,
for compound-commands (if statements, etc.), any redirections must
appear at the end. Redirections are processed after pipelines are
created and in the order they are given, so
cat /foo/bar 2>&1 > /dev/null | cat -n
will print an error with a line number prepended to it.
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
assignment to an integer parameter.
Expression may contain alpha-numeric parameter identifiers, array
references, and integer constants and may be combined with the
following C operators (listed and grouped in increasing order of
precedence).
Unary operators:
+ - ! ~ ++ --
Binary operators:
,
= *= /= %= += -= <<= >>= &= ^= |=
||
&&
|
^
&
== !=
< <= >= >
<< >>
+ -
* / %
Ternary operator:
?: (precedence is immediately higher than assignment)
Grouping operators:
( )
Integer constants may be specified with arbitrary bases using the
notation base#number, where base is a decimal integer specifying the
base, and number is a number in the specified base.
The operators are evaluated as follows:
unary +
result is the argument (included for completeness).
unary -
negation.
! logical not; the result is 1 if argument is zero, 0 if
not.
~ arithmetic (bit-wise) not.
++ increment; must be applied to a parameter (not a literal
or other expression) - the parameter is incremented by 1.
When used as a prefix operator, the result is the
incremented value of the parameter, when used as a
postfix operator, the result is the original value of the
parameter.
-- similar to ++, except the parameter is decremented by 1.
, separates two arithmetic expressions; the left hand side
is evaluated first, then the right. The result is value
of the expression on the right hand side.
= assignment; variable on the left is set to the value on
the right.
*= /= %= += -= <<= >>= &= ^= |=
assignment operators; <var> <op>= <expr> is the same as
<var> = <var> <op> ( <expr> ).
|| logical or; the result is 1 if either argument is non-
zero, 0 if not. The right argument is evaluated only if
the left argument is zero.
&& logical and; the result is 1 if both arguments are non-
zero, 0 if not. The right argument is evaluated only if
the left argument is non-zero.
| arithmetic (bit-wise) or.
^ arithmetic (bit-wise) exclusive-or.
& arithmetic (bit-wise) and.
== equal; the result is 1 if both arguments are equal, 0 if
not.
!= not equal; the result is 0 if both arguments are equal, 1
if not.
< less than; the result is 1 if the left argument is less
than the right, 0 if not.
<= >= >
less than or equal, greater than or equal, greater than.
See <.
<< >> shift left (right); the result is the left argument with
its bits shifted left (right) by the amount given in the
right argument.
+ - * /
addition, subtraction, multiplication, and division.
% remainder; the result is the remainder of the division of
the left argument by the right. The sign of the result
is unspecified if either argument is negative.
<arg1> ? <arg2> : <arg3>
if <arg1> is non-zero, the result is <arg2>, otherwise
<arg3>.
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:
· the only way to close the co-process input (so the co-process
reads an end-of-file) is to redirect the input to a numbered
file descriptor and then close that file descriptor (e.g., exec
3>&p;exec 3>&-).
· in order for co-processes to share a common output, the shell
must keep the write portion of the output pipe open. This means
that end of file will not be detected until all co-processes
sharing the co-process output have exited (when they all exit,
the shell closes its copy of the pipe). This can be avoided by
redirecting the output to a numbered file descriptor (as this
also causes the shell to close its copy). Note that this
behaviour is slightly different from the original Korn shell
which closes its copy of the write portion of the co-process’s
output when the most recently started co-process (instead of
when all sharing co-processes) exits.
· print -p will ignore SIGPIPE signals during writes if the signal
is not being trapped or ignored; the same is not true if the co-
process input has been duplicated to another file descriptor and
print -un is used.
Functions
Functions are defined using either Korn shell function name syntax or
the Bourne/POSIX shell name() syntax (see below for the difference
between the two forms). Functions are like .-scripts in that they are
executed in the current environment, however, unlike .-scripts, shell
arguments (i.e., positional parameters, $1, etc.) are never visible
inside them. When the shell is determining the location of a command,
functions are searched after special built-in commands, and before
regular and non-regular built-ins, and before the PATH is searched.
An existing function may be deleted using unset -f function-name. A
list of functions can be obtained using typeset +f and the function
definitions can be listed using typeset -f. autoload (which is an
alias for typeset -fu) may be used to create undefined functions; when
an undefined function is executed, the shell searches the path
specified in the FPATH parameter for a file with the same name as the
function, which, if found is read and executed. If after executing the
file, the named function is found to be defined, the function is
executed, otherwise, the normal command search is continued (i.e., the
shell searches the regular built-in command table and PATH). Note that
if a command is not found using PATH, an attempt is made to autoload a
function using FPATH (this is an undocumented feature of the original
Korn shell).
Functions can have two attributes, trace and export, which can be set
with typeset -ft and typeset -fx, respectively. When a traced function
is executed, the shell’s xtrace option is turned on for the functions
duration, otherwise the xtrace option is turned off. The export
attribute of functions is currently not used. In the original Korn
shell, exported functions are visible to shell scripts that are
executed.
Since functions are executed in the current shell environment,
parameter assignments made inside functions are visible after the
function completes. If this is not the desired effect, the typeset
command can be used inside a function to create a local parameter.
Note that special parameters (e.g., $$, $!) can’t be scoped in this
way.
The exit status of a function is that of the last command executed in
the function. A function can be made to finish immediately using the
return command; this may also be used to explicitly specify the exit
status.
Functions defined with the function reserved word are treated
differently in the following ways from functions defined with the ()
notation:
· the $0 parameter is set to the name of the function (Bourne-
style functions leave $0 untouched).
· parameter assignments preceding function calls are not kept in
the shell environment (executing Bourne-style functions will
keep assignments).
· OPTIND is saved/reset and restored on entry and exit from the
function so getopts can be used properly both inside and outside
the function (Bourne-style functions leave OPTIND untouched, so
using getopts inside a function interferes with using getopts
outside the function).
Bourne-style function definitions take precedence over alias
dereferences and remove alias definitions upon encounter, while
aliases take precedence over Korn-style functions. In the
future, the following differences will also be added:
· A separate trap/signal environment will be used during the
execution of functions. This will mean that traps set inside a
function will not affect the shell’s traps and signals that are
not ignored in the shell (but may be trapped) will have their
default effect in a function.
· The EXIT trap, if set in a function, will be executed after the
function returns.
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:
· \" 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.
· 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.
· echo options. In POSIX mode, -e and -E are not treated as
options, but printed like other arguments; in non-POSIX mode,
these options control the interpretation of backslash sequences.
· fg exit status: in posix mode, the exit status is 0 if no errors
occur; in non-posix mode, the exit status is that of the last
foregrounded job.
· eval exit status: if eval gets to see an empty command (e.g.,
eval "‘false‘"), its exit status in posix mode will be 0. In
non-posix mode, it will be the exit status of the last command
substitution that was done in the processing of the arguments to
eval (or 0 if there were no command substitutions).
· getopts: in posix mode, options must start with a -; in non-
posix mode, options can start with either - or +.
· brace expansion (also known as alternation): in posix mode,
brace expansion is disabled; in non-posix mode, brace expansion
enabled. Note that set -o posix (or setting the POSIXLY_CORRECT
parameter) automatically turns the braceexpand option off,
however it can be explicitly turned on later.
· set -: in posix mode, this does not clear the verbose or xtrace
options; in non-posix mode, it does.
· set exit status: in posix mode, the exit status of set is 0 if
there are no errors; in non-posix mode, the exit status is that
of any command substitutions performed in generating the set
command. For example, ‘set -- ‘false‘; echo $?’ prints 0 in
posix mode, 1 in non-posix mode. This construct is used in most
shell scripts that use the old getopt(1) command.
(DEBIAN NOTE: This is no longer true on Debian systems. For
compatibility with ksh93, set command always returns exit status
set to 0, regardless of posix or non-posix mode.)
· argument expansion of alias, export, readonly, and typeset
commands: in posix mode, normal argument expansion done; in non-
posix mode, field splitting, file globing, brace expansion and
(normal) tilde expansion are turned off, and assignment tilde
expansion is turned on.
· signal specification: in posix mode, signals can be specified as
digits only if signal numbers match POSIX values (i.e., HUP=1,
INT=2, QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15); in non-
posix mode, signals can be always digits.
· alias expansion: in posix mode, alias expansion is only carried
out when reading command words; in non-posix mode, alias
expansion is carried out on any word following an alias that
ended in a space. For example, the following for loop
alias a=’for ’ i=’j’
a i in 1 2; do echo i=$i j=$j; done
uses parameter i in posix mode, j in non-posix mode.
· test: in posix mode, the expression "-t" (preceded by some
number of "!" arguments) is always true as it is a non-zero
length string; in non-posix mode, it tests if file descriptor 1
is a tty (i.e., the fd argument to the -t test may be left out
and defaults to 1).
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
command below) some special commands are very special in that no field
splitting, file globing, brace expansion nor tilde expansion is
performed on arguments that look like assignments. Regular built-in
commands are different only in that the PATH parameter is not used to
find them.
The original ksh and POSIX differ somewhat in which commands are
considered special or regular:
POSIX special commands
. continue exit return trap
: eval export set unset
break exec readonly shift
Additional ksh special commands
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
without a value, the existing alias is listed. Any name with a
value defines an alias (see Aliases above).
When listing aliases, one of two formats is used: normally,
aliases are listed as name=value, where value is quoted; if
options were preceded with + or a lone + is given on the command
line, only name is printed. In addition, if the -p option is
used, each alias is prefixed with the string "alias ".
The -x option sets (+x clears) the export attribute of an alias,
or, if no names are given, lists the aliases with the export
attribute (exporting an alias has no affect).
The -t option indicates that tracked aliases are to be
listed/set (values specified on the command line are ignored for
tracked aliases). The -r option indicates that all tracked
aliases are to be reset.
The -d causes directory aliases, which are used in tilde
expansion, to be listed or set (see Tilde Expansion above).
bg [job ...]
Resume the specified stopped job(s) in the background. If no
jobs are specified, %+ is assumed. This command is only
available on systems which support job control. See Job Control
below for more information.
bind [-m] [key[=editing-command] ...]
Set or view the current emacs command editing key
bindings/macros. See Emacs Editing Mode below for a complete
description.
break [level]
break exits the levelth inner most for, select, until, or while
loop. level defaults to 1.
builtin command [arg1 ...]
Execute the built-in command command.
cd [-LP] [dir]
Set the working directory to dir. If the parameter CDPATH is
set, it lists directories to search in for dir. An empty entry
in the CDPATH entry means the current directory. If a non-empty
directory from CDPATH is used, the resulting full path is
printed to standard output. If dir is missing, the home
directory $HOME is used. If dir is -, the previous working
directory is used (see OLDPWD parameter). If -L option (logical
path) is used or if the physical option (see set command below)
isn’t set, references to .. in dir are relative to the path used
get to the directory. If -P option (physical path) is used or
if the physical option is set, .. is relative to the filesystem
directory tree. The PWD and OLDPWD parameters are updated to
reflect the current and old wording directory, respectively.
cd [-LP] old new
The string new is substituted for old in the current directory,
and the shell attempts to change to the new directory.
command [-pvV] cmd [arg1 ...]
If neither the -v nor -V options are given, cmd is executed
exactly as if the command had not been specified, with two
exceptions: first, cmd cannot be a shell function, and second,
special built-in commands lose their specialness (i.e.,
redirection and utility errors do not cause the shell to exit,
and command assignments are not permanent). If the -p option is
given, a default search path is used instead of the current
value of PATH (the actual value of the default path is system
dependent: on POSIXish systems, it is the value returned by
getconf CS_PATH
).
If the -v option is given, instead of executing cmd, information
about what would be executed is given (and the same is done for
arg1 ...): for special and regular built-in commands and
functions, their names are simply printed, for aliases, a
command that defines them is printed, and for commands found by
searching the PATH parameter, the full path of the command is
printed. If no command is 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 suppressed if any of
the arguments contain the backslash sequence \c. See print
command below for a list of other backslash sequences that are
recognized.
The options are provided for compatibility with BSD shell
scripts: -n suppresses the trailing newline, -e enables
backslash interpretation (a no-op, since this is normally done),
and -E which suppresses backslash interpretation. If the posix
option is set, only the first argument is treated as an option,
and only if it is exactly -n.
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.
(DEBIAN NOTE: when the shell is called as /bin/sh, it does pass
these file descriptors on, like the Bourne 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
numbers. The -r option reverses the order of the list. Without
-l, the selected commands are edited by the editor specified
with the -e option, or if no -e is specified, the editor
specified by the FCEDIT parameter (if this parameter is not set,
/bin/ed is used), and then executed by the shell.
fc [-e - | -s] [-g] [old=new] [prefix]
Re-execute the selected command (the previous command by
default) after performing the optional substitution of old with
new. If -g is specified, all occurrences of old are replaced
with new. This command is usually accessed with the predefined
alias r=’fc -e -’.
fg [job ...]
Resume the specified job(s) in the foreground. If no jobs are
specified, %+ is assumed. This command is only available on
systems which support job control. See Job Control below for
more information.
getopts optstring name [arg ...]
getopts is used by shell procedures to parse the specified
arguments (or positional parameters, if no arguments are given)
and to check for legal options. optstring contains the option
letters that getopts is to recognize. If a letter is followed
by a colon, the option is expected to have an argument. Options
that do not take arguments may be grouped in a single argument.
If an option takes an argument and the option character is not
the last character of the argument it is found in, the remainder
of the argument is taken to be the option’s argument, otherwise,
the next argument is the option’s argument.
Each time getopts is invoked, it places the next option in the
shell parameter name and the index of the next argument to be
processed in the shell parameter OPTIND. If the option was
introduced with a +, the option placed in name is prefixed with
a +. When an option requires an argument, getopts places it in
the shell parameter OPTARG. When an illegal option or a missing
option argument is encountered a question mark or a colon is
placed in name (indicating an illegal option or missing
argument, respectively) and OPTARG is set to the option
character that caused the problem. An error message is also
printed to standard error if optstring does not begin with a
colon.
When the end of the options is encountered, getopts exits with a
non-zero exit status. Options end at the first (non-option
argument) argument that does not start with a -, or when a --
argument is encountered.
Option parsing can be reset by setting OPTIND to 1 (this is done
automatically whenever the shell or a shell procedure is
invoked).
Warning: Changing the value of the shell parameter OPTIND to a
value other than 1, or parsing different sets of arguments
without resetting OPTIND may lead to unexpected results.
hash [-r] [name ...]
Without arguments, any hashed executable command pathnames are
listed. The -r option causes all hashed commands to be removed
from the hash table. Each name is searched as if it where a
command name and added to the hash table if it is an executable
command.
jobs [-lpn] [job ...]
Display information about the specified jobs; if no jobs are
specified, all jobs are displayed. The -n option causes
information to be displayed only for jobs that have changed
state since the last notification. If the -l option is used,
the process-id of each process in a job is also listed. The -p
option causes only the process group of each job to be printed.
See Job Control below for the format of job and the displayed
job.
kill [-s signame | -signum | -signame ] { job | pid | -pgrp } ...
Send the specified signal to the specified jobs, process ids, or
process groups. If no signal is specified, the signal TERM is
sent. If a job is specified, the signal is sent to the job’s
process group. See Job Control below for the format of job.
kill -l [exit-status ...]
Print the name of the signal that killed a process which exited
with the specified exit-statuses. If no arguments are
specified, a list of all the signals, their numbers and a short
description of them are printed.
let [expression ...]
Each expression is evaluated, see Arithmetic Expressions above.
If all expressions are successfully evaluated, the exit status
is 0 (1) if the last expression evaluated to non-zero (zero).
If an error occurs during the parsing or evaluation of an
expression, the exit status is greater than 1. Since
expressions may need to be quoted, (( expr )) is syntactic sugar
for let "expr".
print [-nprsun | -R [-en]] [argument ...]
Print prints its arguments on the standard output, separated by
spaces, and terminated with a newline. The -n option suppresses
the newline. By default, certain C escapes are translated.
These include \b, \f, \n, \r, \t, \v, and \0### (# is an octal
digit, of which there may be 0 to 3). \c is equivalent to using
the -n option. \ expansion may be inhibited with the -r option.
The -s option prints to the history file instead of standard
output, the -u option prints to file descriptor n (n defaults to
1 if omitted), and the -p option prints to the co-process (see
Co-Processes above).
The -R option is used to emulate, to some degree, the BSD echo
command, which does not process \ sequences unless the -e option
is given. As above, the -n option suppresses the trailing
newline.
pwd [-LP]
Print the present working directory. If -L option is used or if
the physical option (see set command below) isn’t set, the
logical path is printed (i.e., the path used to cd to the
current directory). If -P option (physical path) is used or if
the physical option is set, the path determined from the
filesystem (by following .. directories to the root directory)
is printed.
read [-prsun] [parameter ...]
Reads a line of input from standard input, separate the line
into fields using the IFS parameter (see Substitution above),
and assign each field to the specified parameters. If there are
more parameters than fields, the extra parameters are set to
null, or alternatively, if there are more fields than
parameters, the last parameter is assigned the remaining fields
(inclusive of any separating spaces). If no parameters are
specified, the REPLY parameter is used. If the input line ends
in a backslash and the -r option was not used, the backslash and
newline are stripped and more input is read. If no input is
read, read exits with a non-zero status.
The first parameter may have a question mark and a string
appended to it, in which case the string is used as a prompt
(printed to standard error before any input is read) if the
input is a tty (e.g., read nfoo?’number of foos: ’).
The -un and -p options cause input to be read from file
descriptor n or the current co-process (see Co-Processes above
for comments on this), respectively. If the -s option is used,
input is saved to the history file.
readonly [-p] [parameter[=value]] ...
Sets the readonly attribute of the named parameters. If values
are given, parameters are set to them before setting the
attribute. Once a parameter is made readonly, it cannot be
unset and its value cannot be changed.
If no parameters are specified, the names of all parameters with
the readonly attribute are printed one per line, unless the -p
option is used, in which case readonly commands defining all
readonly parameters, including their values, are printed.
return [status]
Returns from a function or . script, with exit status status.
If no status is given, the exit status of the last executed
command is used. If used outside of a function or . script, it
has the same effect as exit. Note that pdksh treats both
profile and $ENV files as . scripts, while the original Korn
shell only treats profiles as . scripts.
set [+-abCefhkmnpsuvxX] [+-o [option]] [+-A name] [--] [arg ...]
The set command can be used to set (-) or clear (+) shell
options, set the positional parameters, or set an array
parameter. Options can be changed using the +-o option syntax,
where option is the long name of an option, or using the
+-letter syntax, where letter is the option’s single letter name
(not all options have a single letter name). The following
table lists both option letters (if they exist) and long names
along with a description of what the option does.
-A Sets the elements of the array
parameter name to arg ...; If
-A is used, the array is reset
(i.e., emptied) first; if +A
is used, the first N elements
are set (where N is the number
of args), the rest are left
untouched.
-a allexport all new parameters are created
with the export attribute
-b notify Print job notification
messages asynchronously,
instead of just before the
prompt. Only used if job
control is enabled (-m).
-C noclobber Prevent > redirection from
overwriting existing files (>|
must be used to force an
overwrite).
-e errexit Exit (after executing the ERR
trap) as soon as an error
occurs or a command fails
(i.e., exits with a non-zero
status). This does not apply
to commands whose exit status
is explicitly tested by a
shell construct such as if,
until, while, && or ||
statements.
-f noglob Do not expand file name
patterns.
-h trackall Create tracked aliases for all
executed commands (see Aliases
above). On by default for
non-interactive shells.
-i interactive Enable interactive mode - this
can only be set/unset when the
shell is invoked.
-k keyword Parameter assignments are
recognized anywhere in a
command.
-l login The shell is a login shell -
this can only be set/unset
when the shell is invoked (see
Shell Startup above).
-m monitor Enable job control (default
for interactive shells).
-n noexec Do not execute any commands -
useful for checking the syntax
of scripts (ignored if
interactive).
-p privileged Set automatically if, when the
shell starts, the read uid or
gid does not match the
effective uid or gid,
respectively. See Shell
Startup above for a
description of what this
means.
-r restricted Enable restricted mode — this
option can only be used when
the shell is invoked. See
Shell Startup above for a
description of what this
means.
-s stdin If used when the shell is
invoked, commands are read
from standard input. Set
automatically if the shell is
invoked with no arguments.
When -s is used in the set
command, it causes the
specified arguments to be
sorted before assigning them
to the positional parameters
(or to array name, if -A is
used).
-u nounset Referencing of an unset
parameter is treated as an
error, unless one of the -, +
or = modifiers is used.
-v verbose Write shell input to standard
error as it is read.
-x xtrace Print commands and parameter
assignments when they are
executed, preceded by the
value of PS4.
-X markdirs Mark directories with a
trailing / during file name
generation.
bgnice Background jobs are run with
lower priority.
braceexpand Enable brace expansion (aka,
alternation).
emacs Enable BRL emacs-like command
line editing (interactive
shells only); see Emacs
Editing Mode.
gmacs Enable gmacs-like (Gosling
emacs) command line editing
(interactive shells only);
currently identical to emacs
editing except that transpose
(^T) acts slightly
differently.
ignoreeof The shell will not (easily)
exit on when end-of-file is
read, exit must be used. To
avoid infinite loops, the
shell will exit if eof is read
13 times in a row.
nohup Do not kill running jobs with
a HUP signal when a login
shell exists. Currently set
by default, but this will
change in the future to be
compatible with the original
Korn shell (which doesn’t have
this option, but does send the
HUP signal).
nolog No effect - in the original
Korn shell, this prevents
function definitions from
being stored in the history
file.
physical Causes the cd and pwd commands
to use ‘physical’ (i.e., the
filesystem’s) .. directories
instead of ‘logical’
directories (i.e., the shell
handles .., which allows the
user to be oblivious of
symlink links to directories).
Clear by default. Note that
setting this option does not
effect the current value of
the PWD parameter; only the cd
command changes PWD. See the
cd and pwd commands above for
more details.
posix Enable posix mode. See POSIX
Mode above.
sh This option is set only when
ksh was called as a standard
/bin/sh shell. (Note: This
option is a Debian and OpenBSD
addition).
vi Enable vi-like command line
editing (interactive shells
only).
viraw No effect - in the original
Korn shell, unless viraw was
set, the vi command line mode
would let the tty driver do
the work until ESC (^[) was
entered. pdksh is always in
viraw mode.
vi-esccomplete In vi command line editing, do
command / file name completion
when escape (^[) is entered in
command mode.
vi-show8 Prefix characters with the
eighth bit set with ‘M-’. If
this option is not set,
characters in the range
128-160 are printed as is,
which may cause problems.
vi-tabcomplete In vi command line editing, do
command / file name completion
when tab (^I) is entered in
insert mode.
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,
and 1 status if false and greater than 1 if there was an error.
It is normally used as the condition command of if and while
statements. The following basic expressions are available:
str str has non-zero length.
Note that there is the
potential for problems if
str turns out to be an
operator (e.g., -r) - it is
generally better to use a
test like
[ X"str" != X
]
instead (double
quotes are used in
case str contains
spaces or file
globing characters).
-r file file exists and is readable.
-w file file exists and is writable.
-x file file exists and is
executable.
-a file file exists.
-e file file exists.
-f file file is a regular file.
-d file file is a directory.
-c file file is a character special
device.
-b file file is a block special
device.
-p file file is a named pipe.
-u file file’s mode has setuid bit
set.
-g file file’s mode has setgid bit
set.
-k file file’s mode has sticky bit
set.
-s file file is not empty.
-O file file’s owner is the shell’s
effective user-ID.
-G file file’s group is the shell’s
effective group-ID.
-h file file is a symbolic link.
-H file file is a context dependent
directory (only useful on
HP-UX).
-L file file is a symbolic link.
-S file file is a socket.
-o option shell option is set (see set
command above for list of
options). As a non-standard
extension, if the option
starts with a !, the test is
negated; the test always
fails if option doesn’t
exist (thus
[ -o foo -o -o
!foo ]
returns true if and
only if option foo
exists).
file -nt file first file is newer than
second file or first file
exists and the second file
does not.
file -ot file first file is older than
second file or second file
exists and the first file
does not.
file -ef file first file is the same file
as second file.
-t [fd] file descriptor is a tty
device. If the posix option
(set -o posix, see POSIX
Mode above) is not set, fd
may be left out, in which
case it is taken to be 1
(the behaviour differs due
to the special POSIX rules
described below).
string string is not empty.
-z string string is empty.
-n string string is not empty.
string = string strings are equal.
string == string strings are equal.
string != string strings are not equal.
number -eq number numbers compare equal.
number -ne number numbers compare not equal.
number -ge number numbers compare greater than
or equal.
number -gt number numbers compare greater
than.
number -le number numbers compare less than or
equal.
number -lt number numbers compare less than.
The above basic expressions, in which unary operators have
precedence over binary operators, may be combined with the
following operators (listed in increasing order of precedence):
expr -o expr logical or
expr -a expr logical and
! expr logical not
( expr ) grouping
On operating systems not supporting /dev/fd/n devices (where n
is a file descriptor number), the test command will attempt to
fake it for all tests that operate on files (except the -e
test). I.e., [ -w /dev/fd/2 ] tests if file descriptor 2 is
writable.
Note that some special rules are applied (courtesy of POSIX) if
the number of arguments to test or [ ... ] is less than five: if
leading ! arguments can be stripped such that only one argument
remains then a string length test is performed (again, even if
the argument is a unary operator); if leading ! arguments can be
stripped such that three arguments remain and the second
argument is a binary operator, then the binary operation is
performed (even if first argument is a unary operator, including
an unstripped !).
Note: A common mistake is to use if [ $foo = bar ] which fails
if parameter foo is null or unset, if it has embedded spaces
(i.e., IFS characters), or if it is a unary operator like ! or
-n. Use tests like if [ "X$foo" = Xbar ] instead.
time [-p] [ pipeline ]
If a pipeline is given, the times used to execute the pipeline
are reported. If no pipeline is given, then the user and system
time used by the shell itself, and all the commands it has run
since it was started, are reported. The times reported are the
real time (elapsed time from start to finish), the user cpu time
(time spent running in user mode) and the system cpu time (time
spent running in kernel mode). Times are reported to standard
error; the format of the output is:
0.00s real 0.00s user 0.00s system
unless the -p option is given (only possible if pipeline is a
simple command), in which case the output is slightly longer:
real 0.00
user 0.00
sys 0.00
(the number of digits after the decimal may vary from system to
system). Note that simple redirections of standard error do not
effect the output of the time command:
time sleep 1 2> afile
{ time sleep 1; } 2> afile
times for the first command do not go to afile, but those of the
second command do.
times Print the accumulated user and system times used by the shell
and by processes which have exited that the shell started.
trap [handler signal ...]
Sets trap handler that is to be executed when any of the
specified signals are received. Handler is either a null
string, indicating the signals are to be ignored, a minus (-),
indicating that the default action is to be taken for the
signals (see signal(2)), or a string containing shell commands
to be evaluated and executed at the first opportunity (i.e.,
when the current command completes, or before printing the next
PS1 prompt) after receipt of one of the signals. Signal is the
name of a signal (e.g., PIPE or ALRM) or the number of the
signal (see kill -l command above). There are two special
signals: EXIT (also known as 0), which is executed when the
shell is about to exit, and ERR which is executed after an error
occurs (an error is something that would cause the shell to exit
if the -e or errexit option were set — see set command above).
EXIT handlers are executed in the environment of the last
executed command. Note that for non-interactive shells, the
trap handler cannot be changed for signals that were ignored
when the shell started.
With no arguments, trap lists, as a series of trap commands, the
current state of the traps that have been set since the shell
started. Note that the output of trap can not be usefully piped
to another process (an artifact of the fact that traps are
cleared when subprocesses are created).
The original Korn shell’s DEBUG trap and the handling of ERR and
EXIT traps in functions are not yet implemented.
true A command that exits with a zero value.
typeset [[+-Ulprtux] [-L[n]] [-R[n]] [-Z[n]] [-i[n]] | -f [-tux]]
[name[=value] ...]
Display or set parameter attributes. With no name arguments,
parameter attributes are displayed: if no options arg used, the
current attributes of all parameters are printed as typeset
commands; if an option is given (or - with no option letter) all
parameters and their values with the specified attributes are
printed; if options are introduced with +, parameter values are
not printed.
If name arguments are given, the attributes of the named
parameters are set (-) or cleared (+). Values for parameters
may optionally be specified. If typeset is used inside a
function, any newly created parameters are local to the
function.
When -f is used, typeset operates on the attributes of
functions. As with parameters, if no names are given, functions
are listed with their values (i.e., definitions) unless options
are introduced with +, in which case only the function names are
reported.
-Ln Left justify attribute: n specifies the field
width. If n is not specified, the current
width of a parameter (or the width of its
first assigned value) is used. Leading white
space (and zeros, if used with the -Z option)
is stripped. If necessary, values are either
truncated or space padded to fit the field
width.
-Rn Right justify attribute: n specifies the
field width. If n is not specified, the
current width of a parameter (or the width of
its first assigned value) is used. Trailing
white space are stripped. If necessary,
values are either stripped of leading
characters or space padded to make them fit
the field width.
-Zn Zero fill attribute: if not combined with -L,
this is the same as -R, except zero padding
is used instead of space padding.
-in integer attribute: n specifies the base to
use when displaying the integer (if not
specified, the base given in the first
assignment is used). Parameters with this
attribute may be assigned values containing
arithmetic expressions.
-U unsigned integer attribute: integers are
printed as unsigned values (only useful when
combined with the -i option). This option is
not in the original Korn shell.
-f Function mode: display or set functions and
their attributes, instead of parameters.
-l Lower case attribute: all upper case
characters in values are converted to lower
case. (In the original Korn shell, this
parameter meant ‘long integer’ when used with
the -i option).
-p Print complete typeset commands that can be
used to re-create the attributes (but not the
values) of parameters. This is the default
action (option exists for ksh93
compatibility).
-r Readonly attribute: parameters with the this
attribute may not be assigned to or unset.
Once this attribute is set, it can not be
turned off.
-t Tag attribute: has no meaning to the shell;
provided for application use.
For functions, -t is the trace attribute.
When functions with the trace attribute are
executed, the xtrace (-x) shell option is
temporarily turned on.
-u Upper case attribute: all lower case
characters in values are converted to upper
case. (In the original Korn shell, this
parameter meant ‘unsigned integer’ when used
with the -i option, which meant upper case
letters would never be used for bases greater
than 10. See the -U option).
For functions, -u is the undefined attribute.
See Functions above for the implications of
this.
-x Export attribute: parameters (or functions)
are placed in the environment of any executed
commands. Exported functions are not
implemented yet.
ulimit [-acdfHlmnpsStvwL] [value]
Display or set process limits. If no options are used, the file
size limit (-f) is assumed. value, if specified, may be either
be an arithmetic expression or the word unlimited. The limits
affect the shell and any processes created by the shell after a
limit is imposed. Note that some systems may not allow limits
to be increased once they are set. Also note that the types of
limits available are system dependent - some systems have only
the -f limit.
-a Displays all limits; unless -H is used, soft limits are
displayed.
-H Set the hard limit only (default is to set both hard and
soft limits).
-S Set the soft limit only (default is to set both hard and
soft limits).
-c Impose a size limit of n blocks on the size of core
dumps.
-d Impose a size limit of n kbytes on the size of the data
area.
-f Impose a size limit of n blocks on files written by the
shell and its child processes (files of any size may be
read).
-l Impose a limit of n kbytes on the amount of locked
(wired) physical memory.
-m Impose a limit of n kbytes on the amount of physical
memory used.
-n Impose a limit of n file descriptors that can be open at
once.
-p Impose a limit of n processes that can be run by the user
at any one time.
-s Impose a size limit of n kbytes on the size of the stack
area.
-t Impose a time limit of n cpu seconds to be used by each
process.
-v Impose a limit of n kbytes on the amount of virtual
memory used; on some systems this is the maximum
allowable virtual address (in bytes, not kbytes).
-w Impose a limit of n kbytes on the amount of swap space
used.
-L Impose a limit of n locks that can be held on files.
As far as ulimit is concerned, a block is 512 bytes.
umask [-S] [mask]
Display or set the file permission creation mask, or umask (see
umask(2)). If the -S option is used, the mask displayed or set
is symbolic, otherwise it is an octal number.
Symbolic masks are like those used by chmod(1):
[ugoa]{{=+-}{rwx}*}+[,...]
in which the first group of characters is the who part, the
second group is the op part, and the last group is the perm
part. The who part specifies which part of the umask is to be
modified. The letters mean:
u the user permissions
g the group permissions
o the other permissions (non-user, non-group)
a all permissions (user, group and other)
The op part indicates how the who permissions are to be
modified:
= set
+ added to
- removed from
The perm part specifies which permissions are to be set, added
or removed:
r read permission
w write permission
x execute permission
When symbolic masks are used, they describe what permissions may
be made available (as opposed to octal masks in which a set bit
means the corresponding bit is to be cleared). Example:
‘ug=rwx,o=’ sets the mask so files will not be readable,
writable or executable by ‘others’, and is equivalent (on most
systems) to the octal mask ‘07’.
unalias [-adt] [name1 ...]
The aliases for the given names are removed. If the -a option
is used, all aliases are removed. If the -t or -d options are
used, the indicated operations are carried out on tracked or
directory aliases, respectively.
unset [-fv] parameter ...
Unset the named parameters (-v, the default) or functions (-f).
The exit status is non-zero if any of the parameters were
already unset, zero otherwise.
wait [job]
Wait for the specified job(s) to finish. The exit status of
wait is that of the last specified job: if the last job is
killed by a signal, the exit status is 128 + the number of the
signal (see kill -l exit-status above); if the last specified
job can’t be found (because it never existed, or had already
finished), the exit status of wait is 127. See Job Control
below for the format of job. Wait will return if a signal for
which a trap has been set is received, or if a HUP, INT or QUIT
signal is received.
If no jobs are specified, wait waits for all currently running
jobs (if any) to finish and exits with a zero status. If job
monitoring is enabled, the completion status of jobs is printed
(this is not the case when jobs are explicitly specified).
whence [-pv] [name ...]
For each name, the type of command is listed (reserved word,
built-in, alias, function, tracked alias or executable). If the
-p option is used, a path search done even if name is a reserved
word, alias, etc. Without the -v option, whence is similar to
command -v except that whence will find reserved words and won’t
print aliases as alias commands; with the -v option, whence is
the same as command -V. Note that for whence, the -p option
does not affect the search path used, as it does for command.
If the type of one or more of the names could not be determined,
the exit status is non-zero.
Job Control
Job control refers to the shell’s ability to monitor and control jobs,
which are processes or groups of processes created for commands or
pipelines. At a minimum, the shell keeps track of the status of the
background (i.e., asynchronous) jobs that currently exist; this
information can be displayed using the jobs command. If job control is
fully enabled (using set -m or set -o monitor), as it is for
interactive shells, the processes of a job are placed in their own
process group, foreground jobs can be stopped by typing the suspend
character from the terminal (normally ^Z), jobs can be restarted in
either the foreground or background, using the fg and bg commands,
respectively, and the state of the terminal is saved or restored when a
foreground job is stopped or restarted, respectively.
Note that only commands that create processes (e.g., asynchronous
commands, subshell commands, and non-built-in, non-function commands)
can be stopped; commands like read cannot be.
When a job is created, it is assigned a job-number. For interactive
shells, this number is printed inside [..], followed by the process-ids
of the processes in the job when an asynchronous command is run. A job
may be referred to in bg, fg, jobs, kill and wait commands either by
the process id of the last process in the command pipeline (as stored
in the $! parameter) or by prefixing the job-number with a percent sign
(%). Other percent sequences can also be used to refer to jobs:
%+ The most recently stopped job, or, if there
are no stopped jobs, the oldest running job.
%%, % Same as %+.
%- The job that would be the %+ job, if the
later did not exist.
%n The job with job-number n.
%?string The job containing the string string (an
error occurs if multiple jobs are matched).
%string The job starting with string string (an error
occurs if multiple jobs are matched).
When a job changes state (e.g., a background job finishes or foreground
job is stopped), the shell prints the following status information:
[number] flag status command
where
number
is the job-number of the job.
flag is + or - if the job is the %+ or %- job, respectively, or space
if it is neither.
status
indicates the current state of the job and can be
Running
the job has neither stopped or exited (note that running
does not necessarily mean consuming CPU time — the
process could be blocked waiting for some event).
Done [(number)]
the job exited. number is the exit status of the job,
which is omitted if the status is zero.
Stopped [(signal)]
the job was stopped by the indicated signal (if no signal
is given, the job was stopped by SIGTSTP).
signal-description [(core dumped)]
the job was killed by a signal (e.g., Memory fault,
Hangup, etc. — use kill -l for a list of signal
descriptions). The (core dumped) message indicates the
process created a core file.
command
is the command that created the process. If there are multiple
processes in the job, then each process will have a line showing
its command and possibly its status, if it is different from the
status of the previous process.
When an attempt is made to exit the shell while there are jobs in the
stopped state, the shell warns the user that there are stopped jobs and
does not exit. If another attempt is immediately made to exit the
shell, the stopped jobs are sent a HUP signal and the shell exits.
Similarly, if the nohup option is not set and there are running jobs
when an attempt is made to exit a login shell, the shell warns the user
and does not exit. If another attempt is immediately made to exit the
shell, the running jobs are sent a HUP signal and the shell exits.
Interactive Input Line Editing
The shell supports three modes of reading command lines from a tty in
an interactive session. Which is used is controlled by the emacs,
gmacs and vi set options (at most one of these can be set at once). If
none of these options is enabled, the shell simply reads lines using
the normal tty driver. If the emacs or gmacs option is set, the shell
allows emacs like editing of the command; similarly, if the vi option
is set, the shell allows vi like editing of the command. These modes
are described in detail in the following sections.
In these editing modes, if a line is longer that the screen width (see
COLUMNS parameter), a >, + or < character is displayed in the last
column indicating that there are more characters after, before and
after, or before the current position, respectively. The line is
scrolled horizontally as necessary.
Emacs Editing Mode
When the emacs option is set, interactive input line editing is
enabled. Warning: This mode is slightly different from the emacs mode
in the original Korn shell and the 8th bit is stripped in emacs mode.
In this mode various editing commands (typically bound to one or more
control characters) cause immediate actions without waiting for a new-
line. Several editing commands are bound to particular control
characters when the shell is invoked; these bindings can be changed
using the following commands:
bind The current bindings are listed.
bind string=[editing-command]
The specified editing command is bound to the given string,
which should consist of a control character (which may be
written using caret notation ^X), optionally preceded by one of
the two prefix characters. Future input of the string will
cause the editing command to be immediately invoked. Note that
although only two prefix characters (usually ESC and ^X) are
supported, some multi-character sequences can be supported. The
following binds the arrow keys on an ANSI terminal, or xterm
(these are in the default bindings). Of course some escape
sequences won’t work out quite this nicely:
bind ’^[[’=prefix-2
bind ’^XA’=up-history
bind ’^XB’=down-history
bind ’^XC’=forward-char
bind ’^XD’=backward-char
bind -l
Lists the names of the functions to which keys may be bound.
bind -m string=[substitute]
The specified input string will afterwards be immediately
replaced by the given substitute string, which may contain
editing commands.
The following is a list of editing commands available. Each
description starts with the name of the command, a n, if the command
can be prefixed with a count, and any keys the command is bound to by
default (written using caret notation, e.g., ASCII ESC character is
written as ^[). A count prefix for a command is entered using the
sequence ^[n, where n is a sequence of 1 or more digits; unless
otherwise specified, if a count is omitted, it defaults to 1. Note
that editing command names are used only with the bind command.
Furthermore, many editing commands are useful only on terminals with a
visible cursor. The default bindings were chosen to resemble
corresponding EMACS key bindings. The users tty characters (e.g.,
ERASE) are bound to reasonable substitutes and override the default
bindings.
abort ^G
Useful as a response to a request for a search-history pattern
in order to abort the search.
auto-insert n
Simply causes the character to appear as literal input. Most
ordinary characters are bound to this.
backward-char n ^B
Moves the cursor backward n characters.
backward-word n ^[B
Moves the cursor backward to the beginning of a word; words
consist of alphanumerics, underscore (_) and dollar ($).
beginning-of-history ^[<
Moves to the beginning of the history.
beginning-of-line ^A
Moves the cursor to the beginning of the edited input line.
capitalize-word n ^[c, ^[C
Uppercase the first character in the next n words, leaving the
cursor past the end of the last word. If the current line does
not begin with a comment character, one is added at the
beginning of the line and the line is entered (as if return had
been pressed), otherwise the existing comment characters are
removed and the cursor is placed at the beginning of the line.
complete ^[^[
Automatically completes as much as is unique of the command name
or the file name containing the cursor. If the entire remaining
command or file name is unique a space is printed after its
completion, unless it is a directory name in which case / is
appended. If there is no command or file name with the current
partial word as its prefix, a bell character is output (usually
causing a audio beep).
complete-command ^X^[
Automatically completes as much as is unique of the command name
having the partial word up to the cursor as its prefix, as in
the complete command described above.
complete-file ^[^X
Automatically completes as much as is unique of the file name
having the partial word up to the cursor as its prefix, as in
the complete command described above.
complete-list ^[=
List the possible completions for the current word.
delete-char-backward n ERASE, ^?, ^H
Deletes n characters before the cursor.
delete-char-forward n
Deletes n characters after the cursor.
delete-word-backward n ^[ERASE, ^[^?, ^[^H, ^[h
Deletes n words before the cursor.
delete-word-forward n ^[d
Deletes characters after the cursor up to the end of n words.
down-history n ^N
Scrolls the history buffer forward n lines (later). Each input
line originally starts just after the last entry in the history
buffer, so down-history is not useful until either search-
history or up-history has been performed.
downcase-word n ^[L, ^[l
Lowercases the next n words.
end-of-history ^[>
Moves to the end of the history.
end-of-line ^E
Moves the cursor to the end of the input line.
eot ^_ Acts as an end-of-file; this is useful because edit-mode input
disables normal terminal input canonicalization.
eot-or-delete n ^D
Acts as eot if alone on a line; otherwise acts as delete-char-
forward.
error Error (ring the bell).
exchange-point-and-mark ^X^X
Places the cursor where the mark is, and sets the mark to where
the cursor was.
expand-file ^[*
Appends a * to the current word and replaces the word with the
result of performing file globbing on the word. If no files
match the pattern, the bell is rung.
forward-char n ^F
Moves the cursor forward n characters.
forward-word n ^[f
Moves the cursor forward to the end of the nth word.
goto-history n ^[g
Goes to history number n.
kill-line KILL
Deletes the entire input line.
kill-region ^W
Deletes the input between the cursor and the mark.
kill-to-eol n ^K
Deletes the input from the cursor to the end of the line if n is
not specified, otherwise deletes characters between the cursor
and column n.
list ^[?
Prints a sorted, columnated list of command names or file names
(if any) that can complete the partial word containing the
cursor. Directory names have / appended to them.
list-command ^X?
Prints a sorted, columnated list of command names (if any) that
can complete the partial word containing the cursor.
list-file ^X^Y
Prints a sorted, columnated list of file names (if any) that can
complete the partial word containing the cursor. File type
indicators are appended as described under list above.
newline ^J, ^M
Causes the current input line to be processed by the shell. The
current cursor position may be anywhere on the line.
newline-and-next ^O
Causes the current input line to be processed by the shell, and
the next line from history becomes the current line. This is
only useful after an up-history or search-history.
no-op QUIT
This does nothing.
prefix-1 ^[
Introduces a 2-character command sequence.
prefix-2 ^X
prefix-2 ^[[
Introduces a 2-character command sequence.
prev-hist-word n ^[., ^[_
The last (nth) word of the previous command is inserted at the
cursor.
quote ^^
The following character is taken literally rather than as an
editing command.
redraw ^L
Reprints the prompt string and the current input line.
search-character-backward n ^[^]
Search backward in the current line for the nth occurrence of
the next character typed.
search-character-forward n ^]
Search forward in the current line for the nth occurrence of the
next character typed.
search-history ^R
Enter incremental search mode. The internal history list is
searched backwards for commands matching the input. An initial
^ in the search string anchors the search. The abort key will
leave search mode. Other commands will be executed after
leaving search mode. Successive search-history commands
continue searching backward to the next previous occurrence of
the pattern. The history buffer retains only a finite number of
lines; the oldest are discarded as necessary.
set-mark-command ^[<space>
Set the mark at the cursor position.
stuff On systems supporting it, pushes the bound character back onto
the terminal input where it may receive special processing by
the terminal handler. This is useful for the BRL ^T mini-systat
feature, for example.
stuff-reset
Acts like stuff, then aborts input the same as an interrupt.
transpose-chars ^T
If at the end of line, or if the gmacs option is set, this
exchanges the two previous characters; otherwise, it exchanges
the previous and current characters and moves the cursor one
character to the right.
up-history n ^P
Scrolls the history buffer backward n lines (earlier).
upcase-word n ^[U, ^[u
Uppercases the next n words.
version ^V
Display the version of ksh. The current edit buffer is restored
as soon as any key is pressed (the key is then processed, unless
it is a space).
yank ^Y
Inserts the most recently killed text string at the current
cursor position.
yank-pop ^[y
Immediately after a yank, replaces the inserted text string with
the next previous killed text string.
Vi Editing Mode
The vi command line editor in ksh has basically the same commands as
the vi editor (see vi(1)), with the following exceptions:
· you start out in insert mode,
· there are file name and command completion commands (=, \, *,
^X, ^E, ^F and, optionally, <tab>),
· the _ command is different (in ksh it is the last argument
command, in vi it goes to the start of the current line),
· the / and G commands move in the opposite direction as the j
command
· and commands which don’t make sense in a single line editor are
not available (e.g., screen movement commands, ex : commands,
etc.).
Note that the ^X stands for control-X; also <esc>, <space> and <tab>
are used for escape, space and tab, respectively (no kidding).
Like vi, there are two modes: insert mode and command mode. In insert
mode, most characters are simply put in the buffer at the current
cursor position as they are typed, however, some characters are treated
specially. In particular, the following characters are taken from
current tty settings (see stty(1)) and have their usual meaning (normal
values are in parentheses): kill (^U), erase (^?), werase (^W), eof
(^D), intr (^C) and quit (^\). In addition to the above, the following
characters are also treated specially in insert mode:
^H erases previous character
^V literal next: the next character typed is not
treated specially (can be used to insert the
characters being described here)
^J ^M end of line: the current line is read, parsed
and executed by the shell
<esc> puts the editor in command mode (see below)
^E command and file name enumeration (see below)
^F command and file name completion (see below).
If used twice in a row, the list of possible
completions is displayed; if used a third
time, the completion is undone.
^X command and file name expansion (see below)
<tab> optional file name and command completion
(see ^F above), enabled with set -o vi-
tabcomplete
In command mode, each character is interpreted as a command.
Characters that don’t correspond to commands, are illegal combinations
of commands or are commands that can’t be carried out all cause beeps.
In the following command descriptions, a n indicates the command may be
prefixed by a number (e.g., 10l moves right 10 characters); if no
number prefix is used, n is assumed to be 1 unless otherwise specified.
The term ‘current position’ refers to the position between the cursor
and the character preceding the cursor. A ‘word’ is a sequence of
letters, digits and underscore characters or a sequence of non-letter,
non-digit, non-underscore, non-white-space characters (e.g., ab2*&^
contains two words) and a ‘big-word’ is a sequence of non-white-space
characters.
Special ksh vi commands
The following commands are not in, or are different from, the
normal vi file editor:
n_ insert a space followed by the nth big-word from the last
command in the history at the current position and enter
insert mode; if n is not specified, the last word is
inserted.
# insert the comment character (#) at the start of the
current line and return the line to the shell (equivalent
to I#^J).
ng like G, except if n is not specified, it goes to the most
recent remembered line.
nv edit line n using the vi editor; if n is not specified,
the current line is edited. The actual command executed
is ‘fc -e ${VISUAL:-${EDITOR:-vi}} n’.
* and ^X
command or file name expansion is applied to the current
big-word (with an appended *, if the word contains no
file globing characters) - the big-word is replaced with
the resulting words. If the current big-word is the
first on the line (or follows one of the following
characters: ;, |, &, (, )) and does not contain a slash
(/) then command expansion is done, otherwise file name
expansion is done. Command expansion will match the big-
word against all aliases, functions and built-in commands
as well as any executable files found by searching the
directories in the PATH parameter. File name expansion
matches the big-word against the files in the current
directory. After expansion, the cursor is placed just
past the last word and the editor is in insert mode.
n\, n^F, n<tab> and n<esc>
command/file name completion: replace the current big-
word with the longest unique match obtained after
performing command/file name expansion. <tab> is only
recognized if the vi-tabcomplete option is set, while
<esc> is only recognized if the vi-esccomplete option is
set (see set -o). If n is specified, the nth possible
completion is selected (as reported by the command/file
name enumeration command).
= and ^E
command/file name enumeration: list all the commands or
files that match the current big-word.
^V display the version of pdksh; it is displayed until
another key is pressed (this key is ignored).
@c macro expansion: execute the commands found in the alias
_c.
Intra-line movement commands
nh and n^H
move left n characters.
nl and n<space>
move right n characters.
0 move to column 0.
^ move to the first non white-space character.
n| move to column n.
$ move to the last character.
nb move back n words.
nB move back n big-words.
ne move forward to the end the word, n times.
nE move forward to the end the big-word, n times.
nw move forward n words.
nW move forward n big-words.
% find match: the editor looks forward for the nearest
parenthesis, bracket or brace and then moves the to the
matching parenthesis, bracket or brace.
nfc move forward to the nth occurrence of the character c.
nFc move backward to the nth occurrence of the character c.
ntc move forward to just before the nth occurrence of the
character c.
nTc move backward to just before the nth occurrence of the
character c.
n; repeats the last f, F, t or T command.
n, repeats the last f, F, t or T command, but moves in the
opposite direction.
Inter-line movement commands
nj and n+ and n^N
move to the nth next line in the history.
nk and n- and n^P
move to the nth previous line in the history.
nG move to line n in the history; if n is not specified, the
number first remembered line is used.
ng like G, except if n is not specified, it goes to the most
recent remembered line.
n/string
search backward through the history for the nth line
containing string; if string starts with ^, the remainder
of the string must appear at the start of the history
line for it to match.
n?string
same as /, except it searches forward through the
history.
nn search for the nth occurrence of the last search string;
the direction of the search is the same as the last
search.
nN search for the nth occurrence of the last search string;
the direction of the search is the opposite of the last
search.
Edit commands
na append text n times: goes into insert mode just after the
current position. The append is only replicated if
command mode is re-entered (i.e., <esc> is used).
nA same as a, except it appends at the end of the line.
ni insert text n times: goes into insert mode at the current
position. The insertion is only replicated if command
mode is re-entered (i.e., <esc> is used).
nI same as i, except the insertion is done just before the
first non-blank character.
ns substitute the next n characters (i.e., delete the
characters and go into insert mode).
S substitute whole line: all characters from the first non-
blank character to the end of line are deleted and insert
mode is entered.
ncmove-cmd
change from the current position to the position
resulting from n move-cmds (i.e., delete the indicated
region and go into insert mode); if move-cmd is c, the
line starting from the first non-blank character is
changed.
C change from the current position to the end of the line
(i.e., delete to the end of the line and go into insert
mode).
nx delete the next n characters.
nX delete the previous n characters.
D delete to the end of the line.
ndmove-cmd
delete from the current position to the position
resulting from n move-cmds; move-cmd is a movement
command (see above) or d, in which case the current line
is deleted.
nrc replace the next n characters with the character c.
nR replace: enter insert mode but overwrite existing
characters instead of inserting before existing
characters. The replacement is repeated n times.
n~ change the case of the next n characters.
nymove-cmd
yank from the current position to the position resulting
from n move-cmds into the yank buffer; if move-cmd is y,
the whole line is yanked.
Y yank from the current position to the end of the line.
np paste the contents of the yank buffer just after the
current position, n times.
nP same as p, except the buffer is pasted at the current
position.
Miscellaneous vi commands
^J and ^M
the current line is read, parsed and executed by the
shell.
^L and ^R
redraw the current line.
n. redo the last edit command n times.
u undo the last edit command.
U undo all changes that have been made to the current line.
intr and quit
the interrupt and quit terminal characters cause the
current line to be deleted and a new prompt to be
printed.
FILES
~/.profile
/etc/profile
/etc/suid_profile
BUGS
Any bugs in pdksh should be reported to pdksh@cs.mun.ca. Please
include the version of pdksh (echo $KSH_VERSION shows it), the machine,
operating system and compiler you are using and a description of how to
repeat the bug (a small shell script that demonstrates the bug is
best). The following, if relevant (if you are not sure, include them),
can also helpful: options you are using (both options.h options and set
-o options) and a copy of your config.h (the file generated by the
configure script). New versions of pdksh can be obtained from
ftp://ftp.cs.mun.ca/pub/pdksh/.
BTW, the most frequently reported bug is
echo hi | read a; echo $a # Does not print hi
I’m aware of this and there is no need to report it.
VERSION
This page documents version
@(#)PD KSH v5.2.14 99/07/13.2
of the public domain korn shell.
AUTHORS
This shell is based on the public domain 7th edition Bourne shell clone
by Charles Forsyth and parts of the BRL shell by Doug A. Gwyn, Doug
Kingston, Ron Natalie, Arnold Robbins, Lou Salkind and others. The
first release of pdksh was created by Eric Gisin, and it was
subsequently maintained by John R. MacMillan (chance!john@sq.sq.com),
and Simon J. Gerraty (sjg@zen.void.oz.au). The current maintainer is
Michael Rendell (michael@cs.mun.ca). The CONTRIBUTORS file in the
source distribution contains a more complete list of people and their
part in the shell’s development.
SEE ALSO
awk(1), sh(1), csh(1), ed(1), getconf(1), getopt(1), sed(1), stty(1),
vi(1), dup(2), execve(2), getgid(2), getuid(2), open(2), pipe(2),
wait(2), getopt(3), rand(3), signal(3), system(3), environ(7)
The KornShell Command and Programming Language, Morris Bolsky and David
Korn, 1989, ISBN 0-13-516972-0.
UNIX Shell Programming, Stephen G. Kochan, Patrick H. Wood, Hayden.
IEEE Standard for information Technology - Portable Operating System
Interface (POSIX) - Part 2: Shell and Utilities, IEEE Inc, 1993, ISBN
1-55937-255-9.
August 19, 1996