NAME
ksh - Public domain Korn shell
SYNOPSIS
ksh [
±abCefhiklmnprsuvxX] [
±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,
$HOME/.profile and
$ENV if they exist and
are readable.
If the
ENV parameter is set when the shell starts (or, in the case of
login shells, after any profiles are processed), its value is subjected to
parameter, command, arithmetic and tilde substitution and the resulting file
(if any) is read and executed. If the
ENV parameter is not set (and not
null) the file
$HOME/.kshrc is included (after the above mentioned
substitutions have been performed).
The exit status of the shell is 127 if the command file specified on the command
line could not be opened, or non-zero if a fatal syntax error occurred during
the execution of a script. In the absence of fatal errors, the exit status is
that of the last command executed, or zero, if no command is executed.
Command Syntax
The shell begins parsing its input by breaking it into
words. Words,
which are sequences of characters, are delimited by unquoted
white-space characters (space, tab and newline) or
meta-characters (
<,
>,
|,
;,
&,
( and
)). Aside from delimiting words, spaces and
tabs are ignored, while newlines usually delimit commands. The meta-characters
are used in building the following tokens:
<,
<&,
<<,
>,
>&,
>>,
etc.
are used to specify redirections (see Input/Output Redirection below);
| is used to create pipelines;
|& is used to create
co-processes (see Co-Processes below);
; is used to separate commands;
& is used to create asynchronous pipelines;
&& and
|| are used to specify conditional execution;
;; is used in
case statements;
(( ..
)) are used in arithmetic
expressions; and lastly,
( ..
) are used to create subshells.
White-space and meta-characters can be quoted individually using backslash (
\), or in groups using double (
") or single (
')
quotes. Note that the following characters are also treated specially by the
shell and must be quoted if they are to represent themselves:
\,
",
',
#,
$,
`,
~,
{,
},
*,
? and
[. The first three of these are the
above mentioned quoting characters (see Quoting below);
#, if used at
the beginning of a word, introduces a comment — everything after the
# up to the nearest newline is ignored;
$ is used to introduce
parameter, command and arithmetic substitutions (see Substitution below);
` introduces an old-style command substitution (see Substitution
below);
~ begins a directory expansion (see Tilde Expansion below);
{ and
} delimit
csh(1) style alternations (see Brace
Expansion below); and, finally,
*,
? and
[ are used in
file name generation (see File Name Patterns below).
As words and tokens are parsed, the shell builds commands, of which there are
two basic types:
simple-commands, typically programs that are executed,
and
compound-commands, such as
for and
if statements,
grouping constructs and function definitions.
A simple-command consists of some combination of parameter assignments (see
Parameters below), input/output redirections (see Input/Output Redirections
below), and command words; the only restriction is that parameter assignments
come before any command words. The command words, if any, define the command
that is to be executed and its arguments. The command may be a shell built-in
command, a function or an
external command,
i.e., a
separate executable file that is located using the
PATH parameter (see
Command Execution below). Note that all command constructs have an
exit
status: for external commands, this is related to the status returned by
wait(2) (if the command could not be found, the exit status is 127, if
it could not be executed, the exit status is 126); the exit status of other
command constructs (built-in commands, functions, compound-commands,
pipelines, lists,
etc.) are all well defined and are described where
the construct is described. The exit status of a command consisting only of
parameter assignments is that of the last command substitution performed
during the parameter assignment or zero if there were no command
substitutions.
Commands can be chained together using the
| token to form
pipelines, in which the standard output of each command but the last is
piped (see
pipe(2)) to the standard input of the following command. The
exit status of a pipeline is that of its last command. A pipeline may be
prefixed by the
! reserved word which causes the exit status of the
pipeline to be logically complemented: if the original status was 0 the
complemented status will be 1, and if the original status was not 0, then the
complemented status will be 0.
Lists of commands can be created by separating pipelines by any of the
following tokens:
&&,
||,
&,
|&
and
;. The first two are for conditional execution:
cmd1
&& cmd2 executes
cmd2 only if the exit status of
cmd1 is zero;
|| is the opposite —
cmd2 is executed
only if the exit status of
cmd1 is non-zero.
&& and
|| have equal precedence which is higher than that of
&,
|& and
;, which also have equal precedence. The
&
token causes the preceding command to be executed asynchronously, that is, the
shell starts the command, but does not wait for it to complete (the shell does
keep track of the status of asynchronous commands — see Job Control
below). When an asynchronous command is started when job control is disabled (
i.e., in most scripts), the command is started with signals INT and
QUIT ignored and with input redirected from /dev/null (however, redirections
specified in the asynchronous command have precedence). The
|&
operator starts a
co-process which is special kind of asynchronous
process (see Co-Processes below). Note that a command must follow the
&& and
|| operators, while a command need not follow
&,
|& and
;. The exit status of a list is that of
the last command executed, with the exception of asynchronous lists, for which
the exit status is 0.
Compound commands are created using the following reserved words — these
words are only recognized if they are unquoted and if they are used as the
first word of a command (
i.e., they can't be preceded by parameter
assignments or redirections):
case |
else |
function |
then |
! |
do |
esac |
if |
time |
[[ |
done |
fi |
in |
until |
{ |
elif |
for |
select |
while |
} |
Note: Some shells (but not this one) execute control structure commands
in a subshell when one or more of their file descriptors are redirected, so
any environment changes inside them may fail. To be portable, the
exec
statement should be used instead to redirect file descriptors before the
control structure.
In the following compound command descriptions, command lists (denoted as
list) that are followed by reserved words must end with a semi-colon, a
newline or a (syntactically correct) reserved word. For example,
{ echo foo; echo bar; }
{ echo foo; echo bar<newline>}
{ { echo foo; echo bar; } }
are all valid, but
{ echo foo; echo bar }
is not.
- ( list )
- Execute list in a subshell. There is no implicit way
to pass environment changes from a subshell back to its parent.
- { list }
- Compound construct; list is executed, but not in a
subshell. Note that { and } are reserved words, not
meta-characters.
- case word in [ [(]
pattern [ | pattern] ... ) list ;;
] ... esac
- The case statement attempts to match word
against the specified patterns; the list associated with the
first successfully matched pattern is executed. Patterns used in
case statements are the same as those used for file name patterns
except that the restrictions regarding . and / are dropped.
Note that any unquoted space before and after a pattern is stripped; any
space with a pattern must be quoted. Both the word and the patterns are
subject to parameter, command, and arithmetic substitution as well as
tilde substitution. For historical reasons, open and close braces may be
used instead of in and esac (e.g., case $foo { *)
echo bar; }). The exit status of a case statement is that of
the executed list; if no list is executed, the exit status
is zero.
- for name [ in word ...
term ] do list done
- where term is either a newline or a ;. For
each word in the specified word list, the parameter name is
set to the word and list is executed. If in is not used to
specify a word list, the positional parameters ( "$1",
"$2", etc.) are used instead. For historical
reasons, open and close braces may be used instead of do and
done ( e.g., for i; { echo $i; }). The exit status of
a for statement is the last exit status of list; if
list is never executed, the exit status is zero.
- if list then list [elif
list then list] ... [else list]
fi
- If the exit status of the first list is zero, the
second list is executed; otherwise the list following the
elif, if any, is executed with similar consequences. If all the
lists following the if and elifs fail (i.e., exit
with non-zero status), the list following the else is
executed. The exit status of an if statement is that of
non-conditional list that is executed; if no non-conditional
list is executed, the exit status is zero.
- select name [ in word ...
term ] do list done
- where term is either a newline or a ;. The
select statement provides an automatic method of presenting the
user with a menu and selecting from it. An enumerated list of the
specified words is printed on standard error, followed by a prompt
( PS3, normally `#? '). A number corresponding to one of the
enumerated words is then read from standard input, name is set to
the selected word (or is unset if the selection is not valid),
REPLY is set to what was read (leading/trailing space is stripped),
and list is executed. If a blank line ( i.e., zero or more
IFS characters) is entered, the menu is re-printed without
executing list. When list completes, the enumerated list is
printed if REPLY is null, the prompt is printed and so on. This
process is continues until an end-of-file is read, an interrupt is
received or a break statement is executed inside the loop. If in
word ... is omitted, the positional parameters are used (
i.e., "$1", "$2", etc.).
For historical reasons, open and close braces may be used instead of
do and done (e.g., select i; { echo $i; }).
The exit status of a select statement is zero if a break statement
is used to exit the loop, non-zero otherwise.
- until list do list
done
- This works like while, except that the body is
executed only while the exit status of the first list is
non-zero.
- while list do list
done
- A while is a prechecked loop. Its body is executed
as often as the exit status of the first list is zero. The exit
status of a while statement is the last exit status of the
list in the body of the loop; if the body is not executed, the exit
status is zero.
- function name { list
}
- Defines the function name. See Functions below. Note
that redirections specified after a function definition are performed
whenever the function is executed, not when the function definition is
executed.
- name () command
- Mostly the same as function. See Functions
below.
- time [ -p ] [ pipeline ]
- The time reserved word is described in the Command
Execution section.
- (( expression ))
- The arithmetic expression expression is evaluated;
equivalent to let "expression". See
Arithmetic Expressions and the let command below.
- [[ expression ]]
- Similar to the test and [ ... ]
commands (described later), with the following exceptions:
- •
- Field splitting and file name generation are not performed
on arguments.
- •
- The -a (and) and -o (or) operators are
replaced with && and ||, respectively.
- •
- Operators (e.g., -f, =, !,
etc.) must be unquoted.
- •
- The second operand of != and = expressions
are patterns ( e.g., the comparison in [[ foobar = f*r ]]
succeeds).
- •
- There are two additional binary operators: < and
> which return true if their first string operand is less than,
or greater than, their second string operand, respectively.
- •
- The single argument form of test, which tests if the
argument has non-zero length, is not valid - explicit operators must
always be used, e.g., instead of [ str ] use
[[ -n str ]]
- •
- Parameter, command and arithmetic substitutions are
performed as expressions are evaluated and lazy expression evaluation is
used for the && and || operators. This means that in
the statement [[ -r foo && $(< foo) = b*r ]] the
$(< foo) is evaluated if and only if the file foo exists
and is readable.
Quoting
Quoting is used to prevent the shell from treating characters or words
specially. There are three methods of quoting: First,
\ quotes the
following character, unless it is at the end of a line, in which case both the
\ and the newline are stripped. Second, a single quote (
')
quotes everything up to the next single quote (this may span lines). Third, a
double quote (
") quotes all characters, except
$,
`
and
\, up to the next unquoted double quote.
$ and
`
inside double quotes have their usual meaning (
i.e., parameter,
command or arithmetic substitution) except no field splitting is carried out
on the results of double-quoted substitutions. If a
\ inside a
double-quoted string is followed by
\,
$,
` or
", it is replaced by the second character; if it is followed by a
newline, both the
\ and the newline are stripped; otherwise, both the
\ and the character following are unchanged.
Note: An earlier version of ksh(1) changed the interpretation of sequences of
the form
"...
`...
\"...
`..
"
according to whether or not POSIX mode was in effect. In the current
implementation, the backslash in
\" is seen and removed by the
outer
"...
", so the backslash is not seen by the inner
`...
`.
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'
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 losing
null arguments or splitting arguments with spaces).
The following parameters are set and/or used by the shell:
- _ (underscore)
- When an external command is executed by the shell, this
parameter is set in the environment of the new process to the path of the
executed command. In interactive use, this parameter is also set in the
parent shell to the last word of the previous command. When
MAILPATH messages are evaluated, this parameter contains the name
of the file that changed (see MAILPATH parameter below).
- CDPATH
- Search path for the cd built-in command. Works the
same way as PATH for those directories not beginning with /
in cd commands. Note that if CDPATH is set and does not contain
. nor an empty path, the current directory is not searched.
- COLUMNS
- Set to the number of columns on the terminal or window.
Currently set to the cols value as reported by stty(1) if
that value is non-zero. This parameter is used by the interactive line
editing modes, and by select, set -o and kill -l
commands to format information in columns.
- EDITOR
- If the VISUAL parameter is not set, this parameter
controls the command line editing mode for interactive shells. See
VISUAL parameter below for how this works.
- ENV
- If this parameter is found to be set after any profile
files are executed, the expanded value is used as a shell start-up file.
It typically contains function and alias definitions.
- ERRNO
- Integer value of the shell's errno variable —
indicates the reason the last system call failed.
Not implemented yet.
- EXECSHELL
- If set, this parameter is assumed to contain the shell that
is to be used to execute commands that execve(2) fails to execute
and which do not start with a ` #! shell' sequence.
- FCEDIT
- The editor used by the fc command (see below).
- FPATH
- Like PATH, but used when an undefined function is
executed to locate the file defining the function. It is also searched
when a command can't be found using PATH. See Functions below for
more information.
- HISTFILE
- The name of the file used to store history. When assigned
to, history is loaded from the specified file. Also, several invocations
of the shell running on the same machine will share history if their
HISTFILE parameters all point at the same file.
NOTE: if HISTFILE isn't set, no history file is used. This is different from
the original Korn shell, which uses $HOME/.sh_history; in future,
pdksh may also use a default history file.
- HISTSIZE
- The number of commands normally stored for history, default
128.
- HOME
- The default directory for the cd command and the
value substituted for an unqualified ~ (see Tilde Expansion
below).
- IFS
- Internal field separator, used during substitution and by
the read command, to split values into distinct arguments; normally
set to space, tab and newline. See Substitution above for details.
Note: this parameter is not imported from the environment when the
shell is started.
- KSH_VERSION
- The version of shell and the date the version was created
(readonly). See also the version commands in Emacs Editing Mode and Vi
Editing Mode sections, below.
- LINENO
- The line number of the function or shell script that is
currently being executed.
- LINES
- Set to the number of lines on the terminal or window.
Not implemented yet.
- MAIL
- If set, the user will be informed of the arrival of mail in
the named file. This parameter is ignored if the MAILPATH parameter
is set.
- MAILCHECK
- How often, in seconds, the shell will check for mail in the
file(s) specified by MAIL or MAILPATH. If 0, the shell
checks before each prompt. The default is 600 (10 minutes).
- MAILPATH
- A list of files to be checked for mail. The list is colon
separated, and each file may be followed by a ? and a message to be
printed if new mail has arrived. Command, parameter and arithmetic
substitution is performed on the message, and, during substitution, the
parameter $_ contains the name of the file. The default message is
you have mail in $_.
- OLDPWD
- The previous working directory. Unset if cd has not
successfully changed directories since the shell started, or if the shell
doesn't know where it is.
- OPTARG
- When using getopts, it contains the argument for a
parsed option, if it requires one.
- OPTIND
- The index of the last argument processed when using
getopts. Assigning 1 to this parameter causes getopts to
process arguments from the beginning the next time it is invoked.
- PATH
- A colon separated list of directories that are searched
when looking for commands and .'d files. An empty string resulting
from a leading or trailing colon, or two adjacent colons is treated as a
`.', the current directory.
- POSIXLY_CORRECT
- If set, this parameter causes the posix option to be
enabled. See POSIX Mode below.
- PPID
- The process ID of the shell's parent (readonly).
- PS1
- PS1 is the primary prompt for interactive shells.
Parameter, command and arithmetic substitutions are performed, and
! is replaced with the current command number (see fc
command below). A literal ! can be put in the prompt by placing !! in PS1.
Note that since the command line editors try to figure out how long the
prompt is (so they know how far it is to edge of the screen), escape codes
in the prompt tend to mess things up. You can tell the shell not to count
certain sequences (such as escape codes) by prefixing your prompt with a
non-printing character (such as control-A) followed by a carriage return
and then delimiting the escape codes with this non-printing character. If
you don't have any non-printing characters, you're out of luck... BTW,
don't blame me for this hack; it's in the original ksh. Default is `
$ ' for non-root users, ` # ' for root.
- PS2
- Secondary prompt string, by default `> ', used
when more input is needed to complete a command.
- PS3
- Prompt used by select statement when reading a menu
selection. Default is ` #? '.
- PS4
- Used to prefix commands that are printed during execution
tracing (see set -x command below). Parameter, command and
arithmetic substitutions are performed before it is printed. Default is `
+ '.
- PWD
- The current working directory. Maybe unset or null if shell
doesn't know where it is.
- RANDOM
- A simple random number generator. Every time RANDOM
is referenced, it is assigned the next number in a random number series.
The point in the series can be set by assigning a number to RANDOM
(see rand(3)).
- REPLY
- Default parameter for the read command if no names
are given. Also used in select loops to store the value that is
read from standard input.
- SECONDS
- The number of seconds since the shell started or, if the
parameter has been assigned an integer value, the number of seconds since
the assignment plus the value that was assigned.
- TMOUT
- If set to a positive integer in an interactive shell, it
specifies the maximum number of seconds the shell will wait for input
after printing the primary prompt ( PS1). If the time is exceeded,
the shell exits.
- TMPDIR
- The directory shell temporary files are created in. If this
parameter is not set, or does not contain the absolute path of a writable
directory, temporary files are created in /tmp.
- VISUAL
- If set, this parameter controls the command line editing
mode for interactive shells. If the last component of the path specified
in this parameter contains the string vi, emacs or
gmacs, the vi, emacs or gmacs (Gosling emacs) editing mode is
enabled, respectively.
Tilde Expansion
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-processes'
output when the most recently started co-process (instead of when all
sharing co-processes) exits.
- •
- print -p will ignore SIGPIPE signals during writes
if the signal is not being trapped or ignored; the same is not true if the
co-process input has been duplicated to another file descriptor and
print -u n 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). 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:
- •
- kill -l output: in posix mode, signal names are
listed one a single line; in non-posix mode, signal numbers, names and
descriptions are printed in columns. In future, a new option ( -v
perhaps) will be added to distinguish the two behaviours.
- •
- fg exit status: in posix mode, the exit status is 0
if no errors occur; in non-posix mode, the exit status is that of the last
foregrounded job.
- •
- eval exit status: if eval gets to see an empty
command ( e.g., eval "`false`"), its exit status
in posix mode will be 0. In non-posix mode, it will be the exit status of
the last command substitution that was done in the processing of the
arguments to eval (or 0 if there were no command substitutions).
- •
- getopts: in posix mode, options must start with a
-; in non-posix mode, options can start with either - or
+.
- •
- brace expansion (also known as alternation): in posix mode,
brace expansion is disabled; in non-posix mode, brace expansion enabled.
Note that set -o posix (or setting the POSIXLY_CORRECT
parameter) automatically turns the braceexpand option off, however
it can be explicitly turned on later.
- •
- set -: in posix mode, this does not clear the
verbose or xtrace options; in non-posix mode, it does.
- •
- set exit status: in posix mode, the exit status of
set is 0 if there are no errors; in non-posix mode, the exit status is
that of any command substitutions performed in generating the set command.
For example, ` set -- `false`; echo $?' prints 0 in posix mode, 1
in non-posix mode. This construct is used in most shell scripts that use
the old getopt(1) command.
- •
- argument expansion of alias, export,
readonly, and typeset commands: in posix mode, normal
argument expansion done; in non-posix mode, field splitting, file globing,
brace expansion and (normal) tilde expansion are turned off, and
assignment tilde expansion is turned on.
- •
- signal specification: in posix mode, signals can be
specified as digits only if signal numbers match POSIX values (
i.e., HUP=1, INT=2, QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15);
in non-posix mode, signals can be always digits.
- •
- alias expansion: in posix mode, alias expansion is only
carried out when reading command words; in non-posix mode, alias expansion
is carried out on any word following an alias that ended in a space. For
example, the following for loop
alias a='for ' i='j'
a i in 1 2; do echo i=$i j=$j; done
uses parameter
i in posix mode,
j in non-posix mode.
- •
- test: in posix mode, the expression "-t"
(preceded by some number of " !" arguments) is always
true as it is a non-zero length string; in non-posix mode, it tests if
file descriptor 1 is a tty ( i.e., the fd argument to the
-t test may be left out and defaults to 1).
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
-
- Very special commands (non-posix mode)
-
alias |
readonly |
set |
typeset |
|
- POSIX regular commands
-
alias |
command |
fg |
kill |
umask |
bg |
false |
getopts |
read |
unalias |
cd |
fc |
jobs |
true |
wait |
- Additional ksh regular commands
-
[ |
let |
pwd |
ulimit |
|
echo |
print |
test |
whence |
|
In the future, the additional ksh special and regular commands may be treated
differently from the POSIX special and regular commands.
Once the type of the command has been determined, any command line parameter
assignments are performed and exported for the duration of the command.
The following describes the special and regular built-in commands:
- . file [arg1 ...]
- Execute the commands in file in the current
environment. The file is searched for in the directories of PATH.
If arguments are given, the positional parameters may be used to access
them while file is being executed. If no arguments are given, the
positional parameters are those of the environment the command is used
in.
- : [ ... ]
- The null command. Exit status is set to zero.
- alias [ -d | ±t [-r] ]
[±px] [±] [name1[=value1]
...]
- Without arguments, alias lists all aliases. For any
name without a value, the existing alias is listed. Any name with a value
defines an alias (see Aliases above).
When listing aliases, one of two formats is used: normally, aliases are
listed as name=value, where value is quoted;
if options were preceded with + or a lone + is given on the
command line, only name is printed. In addition, if the -p
option is used, each alias is prefixed with the string "
alias ".
The -x option sets (+x clears) the export attribute of an
alias, or, if no names are given, lists the aliases with the export
attribute (exporting an alias has no affect).
The -t option indicates that tracked aliases are to be listed/set
(values specified on the command line are ignored for tracked aliases).
The -r option indicates that all tracked aliases are to be reset.
The -d causes directory aliases, which are used in tilde expansion,
to be listed or set (see Tilde Expansion above).
- bg [job ...]
- Resume the specified stopped job(s) in the background. If
no jobs are specified, %+ is assumed. This command is only
available on systems which support job control. See Job Control below for
more information.
- bind [-l] [-m]
[key[=editing-command] ...]
- Set or view the current emacs command editing key
bindings/macros. See Emacs Editing Mode below for a complete
description.
- break [level]
- break exits the levelth inner most for,
select, until, or while loop. level defaults to 1.
- builtin command [arg1 ...]
- Execute the built-in command command.
- cd [-LP] [dir]
- Set the working directory to dir. If the parameter
CDPATH is set, it lists directories to search in for dir. An
empty entry in the CDPATH entry means the current directory. If a
non-empty directory from CDPATH is used, the resulting full path is
printed to standard output. If dir is missing, the home directory
$HOME is used. If dir is -, the previous working
directory is used (see OLDPWD parameter). If -L option (logical
path) is used or if the physical option (see set command
below) isn't set, references to .. in dir are relative to
the path used get to the directory. If -P option (physical path) is
used or if the physical option is set, .. is relative to the
filesystem directory tree. The PWD and OLDPWD parameters are
updated to reflect the current and old wording directory,
respectively.
- cd [-LP] old new
- The string new is substituted for old in the
current directory, and the shell attempts to change to the new
directory.
- command [-pvV] cmd [arg1
...]
- If neither the -v nor -V options are given,
cmd is executed exactly as if the command had not been
specified, with two exceptions: first, cmd cannot be a shell
function, and second, special built-in commands lose their specialness (
i.e., redirection and utility errors do not cause the shell to
exit, and command assignments are not permanent). If the -p option
is given, a default search path is used instead of the current value of
PATH (the actual value of the default path is system dependent: on
POSIXish systems, it is the value returned by getconf CS_PATH ).
If the -v option is given, instead of executing cmd,
information about what would be executed is given (and the same is done
for arg1 ...): for special and regular built-in commands and
functions, their names are simply printed, for aliases, a command that
defines them is printed, and for commands found by searching the
PATH parameter, the full path of the command is printed. If no
command is found, ( i.e., the path search fails), nothing is
printed and command exits with a non-zero status. The -V
option is like the -v option, except it is more verbose.
- continue [levels]
- continue jumps to the beginning of the
levelth inner most for, select, until, or while loop. level
defaults to 1.
- echo [-neE] [arg ...]
- Prints its arguments (separated by spaces) followed by a
newline, to standard out. The newline is suppressed if any of the
arguments contain the backslash sequence \c. See print
command below for a list of other backslash sequences that are recognized.
The options are provided for compatibility with BSD shell scripts: -n
suppresses the trailing newline, -e enables backslash
interpretation (a no-op, since this is normally done), and -E
suppresses backslash interpretation.
- eval command ...
- The arguments are concatenated (with spaces between them)
to form a single string which the shell then parses and executes in the
current environment.
- exec [command [arg ...]]
- The command is executed without forking, replacing the
shell process.
If no arguments are given, any IO redirection is permanent and the shell is
not replaced. Any file descriptors greater than 2 which are opened or
dup(2)-ed in this way are not made available to other executed
commands ( i.e., commands that are not built-in to the shell). Note
that the Bourne shell differs here: it does pass these file descriptors
on.
- exit [status]
- The shell exits with the specified exit status. If
status is not specified, the exit status is the current value of
the ? parameter.
- export [-p]
[parameter[=value]] ...
- Sets the export attribute of the named parameters. Exported
parameters are passed in the environment to executed commands. If values
are specified, the named parameters also assigned.
If no parameters are specified, the names of all parameters with the export
attribute are printed one per line, unless the -p option is used,
in which case export commands defining all exported parameters,
including their values, are printed.
- false
- A command that exits with a non-zero status.
- fc [-e editor | -l [-n]]
[ -r] [first [last]]
- first and last select commands from the
history. Commands can be selected by history number, or a string
specifying the most recent command starting with that string. The
-l option lists the command on stdout, and -n inhibits the
default command numbers. The -r option reverses the order of the
list. Without -l, the selected commands are edited by the editor
specified with the -e option, or if no -e is specified, the
editor specified by the FCEDIT parameter (if this parameter is not
set, /bin/ed is used), and then executed by the shell.
- fc [-e - | -s] [-g]
[old=new] [prefix]
- Re-execute the selected command (the previous command by
default) after performing the optional substitution of old with
new. If -g is specified, all occurrences of old are
replaced with new. This command is usually accessed with the
predefined alias r='fc -e -'.
- fg [job ...]
- Resume the specified job(s) in the foreground. If no jobs
are specified, %+ is assumed. This command is only available on
systems which support job control. See Job Control below for more
information.
- getopts optstring name [arg
...]
- getopts is used by shell procedures to parse the
specified arguments (or positional parameters, if no arguments are given)
and to check for legal options. optstring contains the option
letters that getopts is to recognize. If a letter is followed by a
colon, the option is expected to have an argument. Options that do not
take arguments may be grouped in a single argument. If an option takes an
argument and the option character is not the last character of the
argument it is found in, the remainder of the argument is taken to be the
option's argument, otherwise, the next argument is the option's argument.
Each time getopts is invoked, it places the next option in the shell
parameter name and the index of the next argument to be processed
in the shell parameter OPTIND. If the option was introduced with a
+, the option placed in name is prefixed with a +.
When an option requires an argument, getopts places it in the shell
parameter OPTARG. When an illegal option or a missing option
argument is encountered a question mark or a colon is placed in
name (indicating an illegal option or missing argument,
respectively) and OPTARG is set to the option character that caused
the problem. An error message is also printed to standard error if
optstring does not begin with a colon.
When the end of the options is encountered, getopts exits with a
non-zero exit status. Options end at the first (non-option) argument that
does not start with a -, or when a -- argument is encountered.
Option parsing can be reset by setting OPTIND to 1 (this is done
automatically whenever the shell or a shell procedure is invoked).
Warning: Changing the value of the shell parameter OPTIND to a value
other than 1, or parsing different sets of arguments without resetting
OPTIND may lead to unexpected results.
- hash [-r] [name ...]
- Without arguments, any hashed executable command pathnames
are listed. The -r option causes all hashed commands to be removed
from the hash table. Each name is searched as if it where a command
name and added to the hash table if it is an executable command.
- jobs [-lpn] [job ...]
- Display information about the specified jobs; if no jobs
are specified, all jobs are displayed. The -n option causes
information to be displayed only for jobs that have changed state since
the last notification. If the -l option is used, the process-id of
each process in a job is also listed. The -p option causes only the
process group of each job to be printed. See Job Control below for the
format of job and the displayed job.
- kill [-s signame | -signum |
-signame ] { job | pid | -pgrp } ...
- Send the specified signal to the specified jobs, process
ids, or process groups. If no signal is specified, the signal TERM is
sent. If a job is specified, the signal is sent to the job's process
group. See Job Control below for the format of job.
- kill -l [exit-status ...]
- Print the name of the signal that killed a process which
exited with the specified exit-statuses. If no arguments are
specified, a list of all the signals, their numbers and a short
description of them are printed.
- let [expression ...]
- Each expression is evaluated, see Arithmetic Expressions
above. If all expressions are successfully evaluated, the exit status is 0
(1) if the last expression evaluated to non-zero (zero). If an error
occurs during the parsing or evaluation of an expression, the exit status
is greater than 1. Since expressions may need to be quoted, ((
expr )) is syntactic sugar for let
"expr ".
- print [-nprsun | -R
[-en]] [ argument ...]
- Print prints its arguments on the standard output,
separated by spaces, and terminated with a newline. The -n option
suppresses the newline. By default, certain C escapes are translated.
These include \b, \f, \n, \r, \t, \v, and \0### (# is an octal digit, of
which there may be 0 to 3). \c is equivalent to using the -n
option. \ expansion may be inhibited with the -r option. The
-s option prints to the history file instead of standard output,
the -u option prints to file descriptor n (n defaults
to 1 if omitted), and the -p option prints to the co-process (see
Co-Processes above).
The -R option is used to emulate, to some degree, the BSD echo
command, which does not process \ sequences unless the -e option is
given. As above, the -n option suppresses the trailing
newline.
- pwd [-LP]
- Print the present working directory. If -L option is
used or if the physical option (see set command below) isn't
set, the logical path is printed ( i.e., the path used to cd
to the current directory). If -P option (physical path) is used or
if the physical option is set, the path determined from the
filesystem (by following .. directories to the root directory) is
printed.
- read [-prsun] [parameter
...]
- Reads a line of input from standard input, separate the
line into fields using the IFS parameter (see Substitution above),
and assign each field to the specified parameters. If there are more
parameters than fields, the extra parameters are set to null, or
alternatively, if there are more fields than parameters, the last
parameter is assigned the remaining fields (inclusive of any separating
spaces). If no parameters are specified, the REPLY parameter is
used. If the input line ends in a backslash and the -r option was
not used, the backslash and newline are stripped and more input is read.
If no input is read, read exits with a non-zero status.
The first parameter may have a question mark and a string appended to it, in
which case the string is used as a prompt (printed to standard error
before any input is read) if the input is a tty ( e.g., read
nfoo?'number of foos: ').
The -un and -p options cause input to be read from file
descriptor n or the current co-process (see Co-Processes above for
comments on this), respectively. If the -s option is used, input is
saved to the history file.
- readonly [-p]
[parameter[=value]] ...
- Sets the readonly attribute of the named parameters. If
values are given, parameters are set to them before setting the attribute.
Once a parameter is made readonly, it cannot be unset and its value cannot
be changed.
If no parameters are specified, the names of all parameters with the
readonly attribute are printed one per line, unless the -p option
is used, in which case readonly commands defining all readonly
parameters, including their values, are printed.
- return [status]
- Returns from a function or . script, with exit
status status. If no status is given, the exit status of the
last executed command is used. If used outside of a function or .
script, it has the same effect as exit. Note that pdksh treats both
profile and $ENV files as . scripts, while the original Korn
shell only treats profiles as . scripts.
- set [±abCefhkmnpsuvxX] [±o
[option]] [±A name] [--] [arg
...]
- The set command can be used to set (-) or clear
(+) shell options, set the positional parameters, or set an array
parameter. Options can be changed using the ±o option
syntax, where option is the long name of an option, or using the
±letter syntax, where letter is the option's
single letter name (not all options have a single letter name). The
following table lists both option letters (if they exist) and long names
along with a description of what the option does.
-A |
|
Sets the elements of the array parameter name to arg
...; If -A is used, the array is reset (i.e., emptied)
first; if +A is used, the first N elements are set (where N is
the number of args), the rest are left untouched. |
-a |
allexport |
all new parameters are created with the export attribute |
-b |
notify |
Print job notification messages asynchronously, instead of just
before the prompt. Only used if job control is enabled (
-m). |
-C |
noclobber |
Prevent > redirection from overwriting existing files
(>| must be used to force an overwrite). |
-e |
errexit |
Exit (after executing the ERR trap) as soon as an error
occurs or a command fails ( i.e., exits with a non-zero
status). This does not apply to commands whose exit status is
explicitly tested by a shell construct such as if,
until, while, && or ||
statements. |
-f |
noglob |
Do not expand file name patterns. |
-h |
trackall |
Create tracked aliases for all executed commands (see Aliases
above). On by default for non-interactive shells. |
-i |
interactive |
Enable interactive mode - this can only be set/unset when the shell
is invoked. |
-k |
keyword |
Parameter assignments are recognized anywhere in a command. |
-l |
login |
The shell is a login shell - this can only be set/unset when the
shell is invoked (see Shell Startup above). |
-m |
monitor |
Enable job control (default for interactive shells). |
-n |
noexec |
Do not execute any commands - useful for checking the syntax of
scripts (ignored if interactive). |
-p |
privileged |
Set automatically if, when the shell starts, the real uid or gid
does not match the effective uid or gid, respectively. See Shell
Startup above for a description of what this means. |
-r |
restricted |
Enable restricted mode — this option can only be used when the
shell is invoked. See Shell Startup above for a description of what
this means. |
-s |
stdin |
If used when the shell is invoked, commands are read from standard
input. Set automatically if the shell is invoked with no arguments.
When -s is used in the set command, it causes the
specified arguments to be sorted before assigning them to the
positional parameters (or to array name, if -A is
used). |
-u |
nounset |
Referencing of an unset parameter is treated as an error, unless one
of the -, + or = modifiers is used. |
-v |
verbose |
Write shell input to standard error as it is read. |
-x |
xtrace |
Print commands and parameter assignments when they are executed,
preceded by the value of PS4. |
-X |
markdirs |
Mark directories with a trailing / during file name
generation. |
|
bgnice |
Background jobs are run with lower priority. |
|
braceexpand |
Enable brace expansion (aka, alternation). |
|
emacs |
Enable BRL emacs-like command line editing (interactive shells
only); see Emacs Editing Mode. |
|
emacs-usemeta |
In emacs command-line editing, use the 8th bit as meta (^[) prefix.
This is the default if LC_CTYPE is unset or POSIX respectively C. 8
|
|
gmacs |
Enable gmacs-like (Gosling emacs) command line editing (interactive
shells only); currently identical to emacs editing except that
transpose (^T) acts slightly differently. |
|
ignoreeof |
The shell will not (easily) exit on when end-of-file is read,
exit must be used. To avoid infinite loops, the shell will exit
if eof is read 13 times in a row. |
|
nohup |
Do not kill running jobs with a HUP signal when a login shell
exists. Currently set by default, but this will change in the future
to be compatible with the original Korn shell (which doesn't have this
option, but does send the HUP signal). |
|
nolog |
No effect - in the original Korn shell, this prevents function
definitions from being stored in the history file. |
|
physical |
Causes the cd and pwd commands to use `physical'
(i.e., the filesystem's) .. directories instead of
`logical' directories ( i.e., the shell handles ..,
which allows the user to be oblivious of symlink links to
directories). Clear by default. Note that setting this option does not
effect the current value of the PWD parameter; only the
cd command changes PWD. See the cd and pwd
commands above for more details. |
|
posix |
Enable posix mode. See POSIX Mode above. |
|
vi |
Enable vi-like command line editing (interactive shells only). |
|
viraw |
No effect - in the original Korn shell, unless viraw was set, the vi
command line mode would let the tty driver do the work until ESC (^[)
was entered. pdksh is always in viraw mode. |
|
vi-esccomplete |
In vi command line editing, do command / file name completion when
escape (^[) is entered in command mode. |
|
vi-show8 |
Prefix characters with the eighth bit set with `M-'. If this option
is not set, characters in the range 128-160 are printed as is, which
may cause problems. |
|
vi-tabcomplete |
In vi command line editing, do command / file name completion when
tab (^I) is entered in insert mode. This is the default. |
These options can also be used upon invocation of the shell. The current set
of options (with single letter names) can be found in the parameter
-. set -o with no option name will list all the options and
whether each is on or off; set +o will print the long names of all
options that are currently on.
Remaining arguments, if any, are positional parameters and are assigned, in
order, to the positional parameters ( i.e., 1, 2,
etc.). If options are ended with -- and there are no
remaining arguments, all positional parameters are cleared. If no options
or arguments are given, then the values of all names are printed. For
unknown historical reasons, a lone - option is treated specially:
it clears both the -x and -v options.
- shift [number]
- The positional parameters number+1, number+2
etc. are renamed to 1, 2, etc. number
defaults to 1.
- test expression
- [ expression ]
- test evaluates the expression and returns
zero status if true, 1 if false, and greater than 1 if there was an error.
It is normally used as the condition command of if and while
statements. The following basic expressions are available:
str |
str has non-zero length. Note that there is the potential for
problems if str turns out to be an operator (e.g.,
-r) - it is generally better to use a test like [
X" str" != X ] instead (double quotes are
used in case str contains spaces or file globing
characters). |
-r file |
file exists and is readable. |
-w file |
file exists and is writable. |
-x file |
file exists and is executable. |
-a file |
file exists. |
-e file |
file exists. |
-f file |
file is a regular file. |
-d file |
file is a directory. |
-c file |
file is a character special device. |
-b file |
file is a block special device. |
-p file |
file is a named pipe. |
-u file |
file's mode has setuid bit set. |
-g file |
file's mode has setgid bit set. |
-k file |
file's mode has sticky bit set. |
-s file |
file is not empty. |
-O file |
file's owner is the shell's effective user-ID. |
-G file |
file's group is the shell's effective group-ID. |
-h file |
file is a symbolic link. |
-H file |
file is a context dependent directory (only useful on
HP-UX). |
-L file |
file is a symbolic link. |
-S file |
file is a socket. |
-o option |
shell option is set (see set command above for list of
options). As a non-standard extension, if the option starts with a
!, the test is negated; the test always fails if option doesn't
exist (thus [ -o foo -o -o !foo ]
returns true if and only if option foo exists). |
file -nt file |
first file is newer than second file or first
file exists and the second file does not. |
file -ot file |
first file is older than second file or second
file exists and the first file does not. |
file -ef file |
first file is the same file as second file. |
-t [fd] |
file descriptor is a tty device. If the posix option (set -o
posix, see POSIX Mode above) is not set, fd may be left
out, in which case it is taken to be 1 (the behaviour differs due to
the special POSIX rules described below). |
string |
string is not empty. |
-z string |
string is empty. |
-n string |
string is not empty. |
string = string |
strings are equal. |
string == string |
strings are equal. |
string != string |
strings are not equal. |
number -eq number |
numbers compare equal. |
number -ne number |
numbers compare not equal. |
number -ge number |
numbers compare greater than or equal. |
number -gt number |
numbers compare greater than. |
number -le number |
numbers compare less than or equal. |
number -lt number |
numbers compare less than. |
The above basic expressions, in which unary operators have precedence over
binary operators, may be combined with the following operators (listed in
increasing order of precedence):
expr -o expr |
logical or |
expr -a expr |
logical and |
! expr |
logical not |
( expr ) |
grouping |
On operating systems not supporting /dev/fd/n devices (where
n is a file descriptor number), the test command will
attempt to fake it for all tests that operate on files (except the
-e test). I.e., [ -w /dev/fd/2 ] tests if file descriptor 2
is writable.
Note that some special rules are applied (courtesy of POSIX) if the number
of arguments to test or [ ... ] is less than five: if
leading ! arguments can be stripped such that only one argument
remains then a string length test is performed (again, even if the
argument is a unary operator); if leading ! arguments can be
stripped such that three arguments remain and the second argument is a
binary operator, then the binary operation is performed (even if first
argument is a unary operator, including an unstripped !).
Note: A common mistake is to use if [ $foo = bar ] which
fails if parameter foo is null or unset, if it has embedded spaces
( i.e., IFS characters), or if it is a unary operator like
! or -n. Use tests like if [ "X$foo" = Xbar
] instead.
- time [-p] [ pipeline ]
- If a pipeline is given, the times used to execute the
pipeline are reported. If no pipeline is given, then the user and system
time used by the shell itself, and all the commands it has run since it
was started, are reported. The times reported are the real time (elapsed
time from start to finish), the user CPU time (time spent running in user
mode) and the system CPU time (time spent running in kernel mode). Times
are reported to standard error; the format of the output is:
0.00s real 0.00s user 0.00s system
unless the -p option is given (only possible if pipeline is a simple
command), in which case the output is slightly longer:
real 0.00
user 0.00
sys 0.00
(the number of digits after the decimal may vary from system to system).
Note that simple redirections of standard error do not effect the output
of the time command: time sleep 1 2> afile { time
sleep 1; } 2> afile times for the first command do not go
to afile, but those of the second command do.
- times
- Print the accumulated user and system times used by the
shell and by processes which have exited that the shell started.
- trap [handler signal ...]
- Sets trap handler that is to be executed when any of the
specified signals are received. Handler is either a null string,
indicating the signals are to be ignored, a minus ( -), indicating
that the default action is to be taken for the signals (see signal(3)), or
a string containing shell commands to be evaluated and executed at the
first opportunity ( i.e., when the current command completes, or
before printing the next PS1 prompt) after receipt of one of the
signals. Signal is the name of a signal (e.g., PIPE or ALRM)
or the number of the signal (see kill -l command above). There are
two special signals: EXIT (also known as 0), which is
executed when the shell is about to exit, and ERR which is executed
after an error occurs (an error is something that would cause the shell to
exit if the -e or errexit option were set — see
set command above). EXIT handlers are executed in the
environment of the last executed command. Note that for non-interactive
shells, the trap handler cannot be changed for signals that were ignored
when the shell started.
With no arguments, trap lists, as a series of trap commands,
the current state of the traps that have been set since the shell started.
Note that the output of trap can not be usefully piped to another
process (an artifact of the fact that traps are cleared when subprocesses
are created).
The original Korn shell's DEBUG trap and the handling of ERR
and EXIT traps in functions are not yet implemented.
- true
- A command that exits with a zero value.
- typeset [[±Ulprtux] [-L[n]]
[-R[ n]] [-Z[n]] [-i[n]] |
-f [ -tux]] [name[=value] ...]
- Display or set parameter attributes. With no name
arguments, parameter attributes are displayed: if no options arg used, the
current attributes of all parameters are printed as typeset commands; if
an option is given (or - with no option letter) all parameters and
their values with the specified attributes are printed; if options are
introduced with +, parameter values are not printed.
If name arguments are given, the attributes of the named parameters
are set ( -) or cleared (+). Values for parameters may
optionally be specified. If typeset is used inside a function, any newly
created parameters are local to the function.
When -f is used, typeset operates on the attributes of functions. As
with parameters, if no names are given, functions are listed with
their values ( i.e., definitions) unless options are introduced
with +, in which case only the function names are reported.
-Ln |
Left justify attribute: n specifies the field width. If
n is not specified, the current width of a parameter (or the
width of its first assigned value) is used. Leading white space (and
zeros, if used with the -Z option) is stripped. If necessary,
values are either truncated or space padded to fit the field
width. |
-Rn |
Right justify attribute: n specifies the field width. If
n is not specified, the current width of a parameter (or the
width of its first assigned value) is used. Trailing white space are
stripped. If necessary, values are either stripped of leading
characters or space padded to make them fit the field width. |
-Zn |
Zero fill attribute: if not combined with -L, this is the
same as -R, except zero padding is used instead of space
padding. |
-in |
integer attribute: n specifies the base to use when
displaying the integer (if not specified, the base given in the first
assignment is used). Parameters with this attribute may be assigned
values containing arithmetic expressions. |
-U |
unsigned integer attribute: integers are printed as unsigned values
(only useful when combined with the -i option). This option is
not in the original Korn shell. |
-f |
Function mode: display or set functions and their attributes,
instead of parameters. |
-l |
Lower case attribute: all upper case characters in values are
converted to lower case. (In the original Korn shell, this parameter
meant `long integer' when used with the -i option). |
-p |
Print complete typeset commands that can be used to re-create the
attributes (but not the values) of parameters. This is the default
action (option exists for ksh93 compatibility). |
-r |
Readonly attribute: parameters with the this attribute may not be
assigned to or unset. Once this attribute is set, it can not be turned
off. |
-t |
Tag attribute: has no meaning to the shell; provided for application
use. For functions, -t is the trace attribute. When functions
with the trace attribute are executed, the xtrace (-x)
shell option is temporarily turned on. |
-u |
Upper case attribute: all lower case characters in values are
converted to upper case. (In the original Korn shell, this parameter
meant `unsigned integer' when used with the -i option, which
meant upper case letters would never be used for bases greater than
10. See the -U option). For functions, -u is the
undefined attribute. See Functions above for the implications of
this. |
-x |
Export attribute: parameters (or functions) are placed in the
environment of any executed commands. Exported functions are not
implemented yet. |
- ulimit [-abcdfHlmnprsStvw]
[value]
- Display or set process limits. If no options are used, the
file size limit ( -f) is assumed. value, if specified, may
be either be an arithmetic expression or the word unlimited. The
limits affect the shell and any processes created by the shell after a
limit is imposed. Note that some systems may not allow limits to be
increased once they are set. Also note that the types of limits available
are system dependent - some systems have only the -f limit.
- -a
- Displays all limits; unless -H is used, soft limits
are displayed.
- -H
- Set the hard limit only (default is to set both hard and
soft limits).
- -S
- Set the soft limit only (default is to set both hard and
soft limits).
- -b
- Impose a size limit of n bytes on the size of socket
buffers.
- -c
- Impose a size limit of n blocks on the size of core
dumps.
- -d
- Impose a size limit of n kbytes on the size of the
data area.
- -f
- Impose a size limit of n blocks on files written by
the shell and its child processes (files of any size may be read).
- -l
- Impose a limit of n kbytes on the amount of locked
(wired) physical memory.
- -m
- Impose a limit of n kbytes on the amount of physical
memory used.
- -n
- Impose a limit of n file descriptors that can be
open at once.
- -r
- Impose a limit of n threads that can be run by the
user at any one time.
- -p
- Impose a limit of n processes that can be run by the
user at any one time.
- -s
- Impose a size limit of n kbytes on the size of the
stack area.
- -t
- Impose a time limit of n CPU seconds to be used by
each process.
- -v
- Impose a limit of n kbytes on the amount of virtual
memory used; on some systems this is the maximum allowable virtual address
(in bytes, not kbytes).
- -w
- Impose a limit of n kbytes on the amount of swap
space used. (Not supported on NetBSD)
As far as
ulimit is concerned, a block is 512 bytes.
- umask [-S] [mask]
Display or set the file permission creation
mask, or umask (see
umask(2)). If the
-S option is used, the
mask displayed or set is symbolic, otherwise it is an octal number.
Symbolic masks are like those used by
chmod(1):
[ugoa]{{=+-}{rwx}*}+[,...]
in which the first group of characters is the
who part, the second group
is the
op part, and the last group is the
perm part. The
who part specifies which part of the umask is to be modified. The
letters mean:
- u
- the user permissions
- g
- the group permissions
- o
- the other permissions (non-user, non-group)
- a
- all permissions (user, group and other)
The
op part indicates how the
who permissions are to be modified:
- =
- set
- +
- added to
- -
- removed from
The
perm part specifies which permissions are to be set, added or
removed:
- r
- read permission
- w
- write permission
- x
- execute permission
When symbolic masks are used, they describe what permissions may be made
available (as opposed to octal masks in which a set bit means the
corresponding bit is to be cleared). Example: `ug=rwx,o=' sets the mask so
files will not be readable, writable or executable by `others', and is
equivalent (on most systems) to the octal mask `07'.
- unalias [-adt] [name1 ...]
- The aliases for the given names are removed. If the
-a option is used, all aliases are removed. If the -t or
-d options are used, the indicated operations are carried out on
tracked or directory aliases, respectively.
- unset [-fv] parameter ...
- Unset the named parameters (-v, the default) or
functions ( -f). The exit status is non-zero if any of the
parameters were already unset, zero otherwise.
- wait [job]
- Wait for the specified job(s) to finish. The exit status of
wait is that of the last specified job: if the last job is killed by a
signal, the exit status is 128 + the number of the signal (see kill
-l exit-status above); if the last specified job can't be found
(because it never existed, or had already finished), the exit status of
wait is 127. See Job Control below for the format of job.
Wait will return if a signal for which a trap has been set is
received, or if a HUP, INT or QUIT signal is received.
If no jobs are specified, wait waits for all currently running jobs
(if any) to finish and exits with a zero status. If job monitoring is
enabled, the completion status of jobs is printed (this is not the case
when jobs are explicitly specified).
- whence [-pv] [name ...]
- For each name, the type of command is listed (reserved
word, built-in, alias, function, tracked alias or executable). If the
-p option is used, a path search done even if name is a
reserved word, alias, etc. Without the -v option,
whence is similar to command -v except that whence
will find reserved words and won't print aliases as alias commands; with
the -v option, whence is the same as command -V. Note
that for whence, the -p option does not affect the search
path used, as it does for command. If the type of one or more of
the names could not be determined, the exit status is non-zero.
Job Control
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 ^[^[
- complete ^I
- Automatically completes as much as is unique of the command
name or the file name containing the cursor. If the entire remaining
command or file name is unique a space is printed after its completion,
unless it is a directory name in which case / is appended. If there
is no command or file name with the current partial word as its prefix, a
bell character is output (usually causing a audio beep).
- complete-command ^X^[
- Automatically completes as much as is unique of the command
name having the partial word up to the cursor as its prefix, as in the
complete command described above.
- complete-file ^[^X
- Automatically completes as much as is unique of the file
name having the partial word up to the cursor as its prefix, as in the
complete command described above.
- complete-list ^[=
- List the possible completions for the current word.
- delete-char-backward n ERASE,
^?, ^H
- Deletes n characters before the cursor.
- delete-char-forward n
- Deletes n characters after the cursor.
- delete-word-backward n ^[ERASE,
^[^?, ^[^H, ^[h
- Deletes n words before the cursor.
- delete-word-forward n ^[d
- Deletes characters after the cursor up to the end of
n words.
- down-history n ^N
- Scrolls the history buffer forward n lines (later).
Each input line originally starts just after the last entry in the history
buffer, so down-history is not useful until either
search-history or up-history has been performed.
- downcase-word n ^[L, ^[l
- Lowercases the next n words.
- end-of-history ^[>
- Moves to the end of the history.
- end-of-line ^E
- Moves the cursor to the end of the input line.
- eot ^_
- Acts as an end-of-file; this is useful because edit-mode
input disables normal terminal input canonicalization.
- eot-or-delete n ^D
- Acts as eot if alone on a line; otherwise acts as
delete-char-forward.
- error
- Error (ring the bell).
- exchange-point-and-mark ^X^X
- Places the cursor where the mark is, and sets the mark to
where the cursor was.
- expand-file ^[*
- Appends a * to the current word and replaces the word with
the result of performing file globbing on the word. If no files match the
pattern, the bell is rung.
- forward-char n ^F
- Moves the cursor forward n characters.
- forward-word n ^[f
- Moves the cursor forward to the end of the nth
word.
- goto-history n ^[g
- Goes to history number n.
- kill-line KILL
- Deletes the entire input line.
- kill-region ^W
- Deletes the input between the cursor and the mark.
- kill-to-eol n ^K
- Deletes the input from the cursor to the end of the line if
n is not specified, otherwise deletes characters between the cursor
and column n.
- list ^[?
- Prints a sorted, columnated list of command names or file
names (if any) that can complete the partial word containing the cursor.
Directory names have / appended to them.
- list-command ^X?
- Prints a sorted, columnated list of command names (if any)
that can complete the partial word containing the cursor.
- list-file ^X^Y
- Prints a sorted, columnated list of file names (if any)
that can complete the partial word containing the cursor. File type
indicators are appended as described under list above.
- newline ^J, ^M
- Causes the current input line to be processed by the shell.
The current cursor position may be anywhere on the line.
- newline-and-next ^O
- Causes the current input line to be processed by the shell,
and the next line from history becomes the current line. This is only
useful after an up-history or search-history.
- no-op QUIT
- This does nothing.
- prefix-1 ^[
- Introduces a 2-character command sequence.
- prefix-2 ^X
- prefix-2 ^[[
- Introduces a 2-character command sequence.
- prev-hist-word n ^[., ^[_
- The last (nth) word of the previous command is
inserted at the cursor.
- quote ^^
- The following character is taken literally rather than as
an editing command.
- redraw ^L
- Reprints the prompt string and the current input line.
- search-character-backward n ^[^]
- Search backward in the current line for the nth
occurrence of the next character typed.
- search-character-forward n ^]
- Search forward in the current line for the nth
occurrence of the next character typed.
- search-history ^R
- Enter incremental search mode. The internal history list is
searched backwards for commands matching the input. An initial ^ in
the search string anchors the search. The abort key will leave search
mode. Other commands will be executed after leaving search mode.
Successive search-history commands continue searching backward to
the next previous occurrence of the pattern. The history buffer retains
only a finite number of lines; the oldest are discarded as necessary.
- set-mark-command ^[<space>
- Set the mark at the cursor position.
- stuff
- On systems supporting it, pushes the bound character back
onto the terminal input where it may receive special processing by the
terminal handler. This is useful for the BRL ^T mini-systat
feature, for example.
- stuff-reset
- Acts like stuff, then aborts input the same as an
interrupt.
- transpose-chars ^T
- If at the end of line, or if the gmacs option is
set, this exchanges the two previous characters; otherwise, it exchanges
the previous and current characters and moves the cursor one character to
the right.
- up-history n ^P
- Scrolls the history buffer backward n lines
(earlier).
- upcase-word n ^[U, ^[u
- Uppercases the next n words.
- version ^V
- Display the version of ksh. The current edit buffer is
restored as soon as any key is pressed (the key is then processed, unless
it is a space).
- yank ^Y
- Inserts the most recently killed text string at the current
cursor position.
- yank-pop ^[y
- Immediately after a yank, replaces the inserted text
string with the next previous killed text string.
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
~/.kshrc
~/.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.