sh - public domain Bourne shell
sh [-+abCefhiklmnprsuvxX] [-+o option]
[[-c command-string [command-name] | -s | file] [argument
...]]
sh is a reimplementation of the Bourne shell, a command interpreter for
both interactive and script use.
Shell startup [Toc] [Back]
The following options can be specified only on the command
line:
-c command-string
sh will execute the command(s) contained in
command-string.
-i Interactive mode; see below.
-l Login shell; see below.
-s The shell reads commands from standard input; all
non-option arguments
are positional parameters.
-r Restricted mode; see below.
In addition to the above, the options described in the set
built-in command
can also be used on the command line.
If neither the -c nor the -s option is specified, the first
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 the
standard input. The name of the shell (i.e., the contents
of $0) is determined
as follows: if the -c option is used and there is a
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 SIGINT,
SIGQUIT, and
SIGTERM signals, and prints prompts before reading input
(see PS1 and PS2
parameters). For non-interactive shells, the trackall option is on by
default (see the set command below).
A shell is ``restricted'' if the -r option is used or if either the basename
of the name the shell was invoked with or the SHELL parameter match
the pattern ``*r*sh'' (e.g., ``rsh'', ``rksh'', ``rpdksh'',
etc.). The
following restrictions come into effect after the shell processes any
profile and ENV files:
+o The cd command is disabled.
+o The SHELL, ENV, and PATH parameters cannot be changed.
+o Command names can't be specified with absolute or relative paths.
+o The -p option of the built-in command command can't be
used.
+o Redirections that create files can't be used (i.e., `>',
`>|', `>>',
`<>').
A shell is ``privileged'' if the -p option is used or if the
real user ID
or group ID does not match the effective user ID or group ID
(see
getuid(2) and getgid(2)). A privileged shell does not process
$HOME/.profile nor the ENV parameter (see below). Instead,
the file
/etc/suid_profile is processed. Clearing the privileged option causes
the shell to set its effective user ID (group ID) to its real user ID
(group ID).
If the basename of the name the shell is called with (i.e.,
argv[0])
starts with `-' or if the -l option is used, the shell is
assumed to be a
login shell and the shell reads and executes the contents of
/etc/profile
and $HOME/.profile if they exist and are readable.
If the ENV parameter is set when the shell starts (or, in
the case of login
shells, after any profiles are processed), its value is
subjected to
parameter, command, arithmetic, and tilde (`~') substitution
and the resulting
file (if any) is read and executed. If the ENV parameter is not
set (and not NULL) and pdksh was compiled with the DEFAULT_ENV macro defined,
the file named in that macro is included (after the
above mentioned
substitutions have been performed).
The exit status of the shell is 127 if the command file
specified on the
command line could not be opened, or non-zero if a fatal
syntax error occurred
during the execution of a script. In the absence of
fatal errors,
the exit status is that of the last command executed, or zero, if no command
is executed.
Command syntax [Toc] [Back]
The shells begins parsing its input by breaking it into
words. Words,
which are sequences of characters, are delimited by unquoted
whitespace
characters (space, tab, and newline) or meta-characters
(`<', `>', `|',
`;', `(', and `)'). Aside from delimiting words, spaces and
tabs are ignored,
while newlines usually delimit commands. The metacharacters are
used in building the following tokens: `<', `<&', `<<', `>',
`>&', `>>',
etc. are used to specify redirections (see Input/output
redirection below);
`|' is used to create pipelines; `;' is used to separate commands;
`&' is used to create asynchronous pipelines; `&&' and `||'
are used to
specify conditional execution; `;;' is used in case statements; and lastly,
`( .. )' is used to create subshells.
Whitespace and meta-characters can be quoted individually
using a backslash
(`'), or in groups using double (`"') or single (`'')
quotes.
Note that the following characters are also treated specially by the
shell and must be quoted if they are to represent themselves: `', `"',
`'', `#', `$', ``', `~', `{', `}', `*', `?', 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 alterations (see Brace
expansion below); and finally, `*', `?', and `[' are used in
file name
generation (see File name patterns below).
As words and tokens are parsed, the shell builds commands,
of which there
are two basic types: simple-commands, typically programs
that are executed,
and compound-commands, such as for and if statements,
grouping constructs,
and function definitions.
A simple-command consists of some combination of parameter
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 0 is
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; if the original status was not 0, the complemented status
will be 0.
Lists of commands can be created by separating pipelines by
any of the
following tokens: `&&', `||', `&', `|&', and `;'. The first
two are for
conditional execution: ``cmd1 && cmd2'' executes cmd2 only
if the exit
status of cmd1 is zero; `||' is the opposite -- cmd2 is executed only if
the exit status of cmd1 is non-zero. `&&' and `||' have
equal precedence
which is higher than that of `&', `|&', and `;', which also
have equal
precedence. Note that the `&&' and `||' operators are
"leftassociative".
For example, both of these commands will
print only "bar":
false && echo foo || echo bar
true || echo foo && echo bar
The `&' token causes the preceding command to be executed
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 SIGINT and SIGQUIT ignored and with input redirected
from
/dev/null (however, redirections specified in the asynchronous command
have precedence). Note that a command must follow the `&&'
and `||' operators,
while it need not follow `&', `|&', or `;'. The
exit status of
a list is that of the last command executed, with the exception of asynchronous
lists, for which the exit status is 0.
Compound commands are created using the following reserved
words. These
words are only recognized if they are unquoted and if they
are used as
the first word of a command (i.e., they can't be preceded by
parameter
assignments or redirections):
case else function !
do esac if until [[
done fi in while {
elif for time then }
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
semicolon, 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
within 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
For each word in the specified word list, the parameter name is
set to the word and list is executed. If in is not
used to specify
a word list, the positional parameters ($1, $2,
etc.) are
used instead. For historical reasons, open and
close braces may
be used instead of do and done (e.g., for i; { echo
$i; }). The
exit status of a for statement is the last exit status of list;
if list is never executed, the exit status is zero.
term is either
a newline or a `;'.
if list then list [elif list then list] ... [else list] fi
If the exit status of the first list is zero, the
second list is
executed; otherwise, the list following the elif, if
any, is executed
with similar consequences. If all the lists
following the
if and elifs fail (i.e., exit with non-zero status),
the list
following the else is executed. The exit status of
an if statement
is that of non-conditional list that is executed; if no nonconditional
list is executed, the exit status is zero.
until list do list done
This works like while, except that the body is executed only
while the exit status of the first list is non-zero.
while list do list done
A while is a pre-checked loop. Its body is executed
as often as
the exit status of the first list is zero. The exit
status of a
while statement is the last exit status of the list
in the body
of the loop; if the body is not executed, the exit
status is zero.
function name { list }
Defines the function name (see Functions below).
Note that redirections
specified after a function definition are
performed
whenever the function is executed, not when the
function definition
is executed.
name () command
Mostly the same as function (see Functions below).
Quoting [Toc] [Back]
Quoting is used to prevent the shell from treating characters or words
specially. There are three methods of quoting. First, `'
quotes the
following character, unless it is at the end of a line, in
which case
both the `' and the newline are stripped. Second, a single
quote (`'')
quotes everything up to the next single quote (this may span
lines).
Third, a double quote (`"') quotes all characters, except
`$', ``' and
`', up to the next unquoted double quote. `$' and ``' inside double
quotes have their usual meaning (i.e., parameter, command or
arithmetic
substitution) except no field splitting is carried out on
the results of
double-quoted substitutions. If a `' inside a double-quoted
string is
followed by `', `$', ``', or `"', it is replaced by the second character;
if it is followed by a newline, both the `' and the
newline are
stripped; otherwise, both the `' and the character following
are unchanged.
Note: See POSIX mode below for a special rule regarding sequences of the
form "...`...
Aliases [Toc] [Back]
There are two types of aliases: normal command aliases and
tracked aliases.
Command aliases are normally used as a short hand for a
long or often
used command. The shell expands command aliases (i.e.,
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:
hash='alias -t'
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 [Toc] [Back]
The first step the shell takes in executing a simple-command
is to perform
substitutions on the words of the command. There are
three kinds of
substitution: parameter, command, and arithmetic. Parameter
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 whitespace''. Sequences
of one or
more IFS whitespace characters, in combination with zero or
one non-IFS
whitespace characters, delimit a field. As a special case,
leading and
trailing IFS whitespace is stripped (i.e., no leading or
trailing empty
field is created by it); leading or trailing non-IFS whitespace does create
an empty field.
Example: If IFS is set to ``<space>:'', and VAR is set to
``<space>A<space>:<space><space>B::D'', the substitution for
$VAR results
in 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.
Also, note that the field splitting applies only to the immediate result
of the substitution. Using the previous example, the substitution for
$VAR:E results in the fields: ``A'', ``B'', ``'', and
``D:E'', not ``A'',
``B'', ``'', and ``E''. This behavior is POSIX compliant,
but incompatible
with some other shell implementations which do field
splitting on the
word which contained the substitution or use IFS as a general whitespace
delimiter.
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 (note that $(< foo) has
the same effect
as $(cat foo), but it is carried out more efficiently
because no
process is started).
Note: $(command) expressions are currently parsed by finding
the matching
parenthesis, regardless of quoting. This should be fixed
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 [Toc] [Back]
Parameters are shell variables; they can be assigned values
and their
values can be accessed using a parameter substitution. A
parameter name
is either one of the special single punctuation or digit
character parameters
described below, or a letter followed by zero or more
letters or
digits (`_' counts as a letter). Parameter substitutions
take the form
$name or ${name}, where name is a parameter name. If substitution is
performed on a parameter that is not set, a null string is
substituted
unless the nounset option (set -o nounset or set -u) is set,
in which
case an error occurs.
Parameters can be assigned values in a number of ways.
First, the shell
implicitly sets some parameters like #, PWD, etc.; this is
the only way
the special single character parameters are set. Second,
parameters are
imported from the shell's environment at startup. Third,
parameters can
be assigned values on the command line, for example, FOO=bar
sets the parameter
FOO to ``bar''; multiple parameter assignments can
be given on a
single command line and they can be followed by a simplecommand, in
which case the assignments are in effect only for the duration of the
command (such assignments are also exported, see below for
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
loops set parameters as well as the getopts, read and set -A
commands.
Lastly, parameters can be assigned values using assignment
operators inside
arithmetic expressions (see Arithmetic expressions below) or using
the ${name=value} form of the parameter substitution (see
below).
Parameters with the export attribute (set using the export
or typeset -x
commands, or by parameter assignments followed by simple
commands) are
put in the environment (see environ(7)) of commands run by
the shell as
name=value pairs. The order in which parameters appear in
the environment
of a command is unspecified. When the shell starts up,
it extracts
parameters and their values from its environment and automatically sets
the export attribute for those parameters.
Modifiers can be applied to the ${name} form of parameter
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 `*',
`@', not
specified, or the length of the string value of parameter name.
${#name[*]}, ${#name[@]}
The number of elements in the array name.
${name#pattern}, ${name##pattern}
If pattern matches the beginning of the value of parameter name,
the matched text is deleted from the result of substitution. A
single `#' results in the shortest match, and two of
them result
in the longest match.
${name%pattern}, ${name%%pattern}
Like ${..#..} substitution, but it deletes from the
end of the
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. Do NOT use this mechanism for
generating temporary
file names; see mktemp(1) instead.
- The concatenation of the current single letter options (see the
set command below for a list of options).
? The exit status of the last non-asynchronous command executed.
If the last command was killed by a signal, $? is
set to 128
plus the signal number.
0 The name the shell was invoked with (i.e.,
argv[0]), or the
command-name if it was invoked with the -c option
and the
command-name was supplied, or the file argument, if
it was supplied.
If the posix option is not set, $0 is the
name of the
current function or script.
1 ... 9 The first nine positional parameters that were supplied to the
shell, function or .-script. Further positional
parameters may
be accessed using ${number}.
* All positional parameters (except parameter 0);
i.e., $1, $2,
$3, ... If used outside of double quotes, parameters are separate
words (which are subjected to word splitting);
if used
within double quotes, parameters are separated by
the first
character of the IFS parameter (or the empty string
if IFS is
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:
CDPATH Search path for the cd built-in command. Works
the same way
as PATH for those directories not beginning with
`/' in cd
commands. Note that if CDPATH is set and does
not contain
``.'' or contains an empty path, the current directory is not
searched. Also, the cd built-in command will
display the resulting
directory when a match is found in any
search path
other than the empty path.
COLUMNS Set to the number of columns on the terminal or
window. Currently
set to the ``cols'' value as reported by
stty(1) if
that value is non-zero. This parameter is used
by the set -o
and kill -l commands to format information
columns.
ENV If this parameter is found to be set after any
profile files
are executed, the expanded value is used as a
shell startup
file. It typically contains function and alias
definitions.
ERRNO Integer value of the shell's errno variable. It
indicates the
reason the last system call failed. Not yet implemented.
EXECSHELL If set, this parameter is assumed to contain the
shell that is
to be used to execute commands that execve(2)
fails to execute
and which do not start with a ``#!shell'' sequence.
FCEDIT The editor used by the fc command (see below).
FPATH Like PATH, but used when an undefined function is
executed to
locate the file defining the function. It is also searched
when a command can't be found using PATH. See
Functions below
for more information.
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.
SH_VERSION
The version of shell and the date the version was
created
(read-only).
LINENO The line number of the function or shell script
that is currently
being executed.
LINES Set to the number of lines on the terminal or
window. Not yet
implemented.
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 (read-only).
PS1 The prompt is printed verbatim (i.e., no substitutions are
done). Default is ``$ '' for non-root users, ``#
'' for root.
PS2 Secondary prompt string, by default ``> '', used
when more input
is needed to complete a command.
PS4 Used to prefix commands that are printed during
execution
tracing (see the set -x command below). The
prompt is printed
verbatim (i.e., no substitutions are done). Default is
``+ ''.
PWD The current working directory. May be unset or
NULL if the
shell doesn't know where it is.
REPLY Default parameter for the read command if no
names are given.
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.
Tilde expansion [Toc] [Back]
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 reused.
The alias -d command may be used to list, change, and
add to this
cache (e.g., alias -d fac=/usr/local/facilities; cd
~fac/bin).
File name patterns [Toc] [Back]
A file name pattern is a word containing one or more unquoted `?' or `*'
characters or ``[..]'' sequences. Once brace expansion has
been performed,
the shell replaces file name patterns with the sorted names of
all the files that match the pattern (if no files match, the
word is left
unchanged). The pattern elements have the following meaning:
? Matches any single character.
* Matches any sequence of characters.
[..] Matches any of the characters inside the brackets.
Ranges of
characters can be specified by separating two characters by a `-'
(e.g., ``[a0-9]'' matches the letter ``a'' or any
digit). In order
to represent itself, a `-' must either be quoted
or the first
or last character in the character list. Similarly,
a `]' must
be quoted or the first character in the list if it
is to represent
itself instead of the end of the list. Also, a
`!' appearing
at the start of the list has special meaning
(see below), so
to represent itself it must be quoted or appear later in the
list.
[!..] Like [..], except it matches any character not inside the brackets.
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'',
``foobar'', etc.
?(pattern| ... |pattern)
Matches the empty string or a string that matches
one of the
specified patterns. Example: The pattern ?(foo|bar)
only matches
the strings ``'', ``foo'' and ``bar''.
@(pattern| ... |pattern)
Matches a string that matches one of the specified
patterns. Example:
The pattern @(foo|bar) only matches the
strings ``foo''
and ``bar''.
!(pattern| ... |pattern)
Matches any string that does not match one of the
specified patterns.
Examples: The pattern !(foo|bar) matches all
strings except
``foo'' and ``bar''; the pattern !(*) matches
no strings;
the pattern !(?)* matches all strings (think about
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 if file exists it is appended to
instead of being
truncated. Also, the file is opened in append
mode, so
writes always go to the end of the file (see
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
`0wline'. If multiple here documents are used on
the same command
line, they are saved in order.
<<- marker
Same as <<, except leading tabs are stripped from
lines in the
here document.
<& fd Standard input is duplicated from file descriptor
fd. fd can be
a single digit, indicating the number of an existing
file descriptor;
the letter `p', indicating the file descriptor associated
with the output of the current co-process; or
the character
`-', indicating standard input is to be closed.
>& fd Same as <&, except the operation is done on standard
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 expanded file name generation characters
is used. Note that in restricted shells, redirections
which can
create files cannot be used.
For simple-commands, redirections may appear anywhere in the
command; for
compound-commands (if statements, etc.), any redirections
must appear at
the end. Redirections are processed after pipelines are
created and in
the order they are given, so
cat /foo/bar 2>&1 > /dev/null | cat -n
will print an error with a line number prepended to it.
Arithmetic expressions [Toc] [Back]
Integer arithmetic expressions can be used with the let command, inside
$((..)) expressions, inside array references (e.g.,
name[expr]), as numeric
arguments to the test command, and as the value of an
assignment to
an integer parameter.
Expressions may contain alpha-numeric parameter identifiers,
array references,
and integer constants and may be combined with the
following C operators
(listed and grouped in increasing order of precedence):
Unary operators:
+ - ! ~ ++ --
Binary operators:
,
= *= /= %= += -= <<= >>= &= ^= |=
||
&&
|
^
&
== !=
< <= >= >
<< >>
+ -
* / %
Ternary operators:
?: (precedence is immediately higher than assignment)
Grouping operators:
( )
Integer constants may be specified with arbitrary bases using the notation
base#number, where base is a decimal integer specifying
the base,
and number is a number in the specified base.
The operators are evaluated as follows:
unary +
Result is the argument (included for completeness).
unary -
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 the 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) XOR (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>.
Functions [Toc] [Back]
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, $2, etc.) are never visible
inside them.
When the shell is determining the location of a command,
functions are
searched after special built-in commands, 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. The autoload command
(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 function's
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:
+o The $0 parameter is set to the name of the function
(Bourne-style
functions leave $0 untouched).
+o Parameter assignments preceding function calls are not
kept in the
shell environment (executing Bourne-style functions will
keep assignments).
+o OPTIND is saved/reset and restored on entry and exit
from the function
so getopts can be used properly both inside and
outside the
function (Bourne-style functions leave OPTIND untouched,
so using
getopts inside a function interferes with using getopts
outside the
function). In the future, the following differences
will also be
added:
+o A separate trap/signal environment will be
used during the
execution of functions. This will mean that
traps set inside
a function will not affect the shell's
traps and signals
that are not ignored in the shell (but
may be trapped)
will have their default effect in a function.
+o The EXIT trap, if set in a function, will be
executed after
the function returns.
POSIX mode [Toc] [Back]
The shell is intended to be POSIX compliant; however, in
some cases,
POSIX behaviour is contrary either to the original Korn
shell behaviour
or to user convenience. How the shell behaves in these cases is determined
by the state of the posix option (set -o posix). If
it is on, the
POSIX behaviour is followed; otherwise, it is not. The
posix option is
set automatically when the shell starts up if the environment contains
the POSIXLY_CORRECT parameter. (The shell can also be compiled so that it
is in POSIX mode by default; however, this is usually not
desirable).
The following is a list of things that are affected by the
state of the
posix option:
+o Reading of $ENV. If not in posix mode, the ENV parameter is not expanded
and included when the shell starts.
+o Occurrences of
In POSIX mode, the
in non-POSIX mode, the backslash is stripped before the
command substitution
is interpreted. For example, echo "`echo
``"hi"'' in POSIX mode, ``hi'' in non-POSIX mode. To
avoid problems,
use the $(...) form of command substitution.
+o kill -l output. In POSIX mode, signal names are listed
one per line;
in non-POSIX mode, signal numbers, names, and descriptions are printed
in columns. In future, a new option (-v perhaps)
will be added to
distinguish the two behaviours.
+o fg exit status. In POSIX mode, the exit status is 0 if
no errors occur;
in non-POSIX mode, the exit status is that of the
last foregrounded
job.
+o getopts. In POSIX mode, options must start with a `-';
in non-POSIX
mode, options can start with either `-' or `+'.
+o Brace expansion (also known as alternation). In POSIX
mode, brace
expansion is disabled; in non-POSIX mode, brace expansion is enabled.
Note that set -o posix (or setting the POSIXLY_CORRECT
parameter) automatically
turns the braceexpand option off; however,
it can be explicitly
turned on later.
+o set -. In POSIX mode, this does not clear the verbose
or xtrace options;
in non-POSIX mode, it does.
+o set exit status. In POSIX mode, the exit status of set
is 0 if there
are no errors; in non-POSIX mode, the exit status is
that of any command
substitutions performed in generating the set command. For example,
set -- `false`; echo $? prints 0 in POSIX mode, 1
in non-POSIX
mode. This construct is used in most shell scripts that
use the old
getopt(1) command.
+o Argument expansion of the alias, export, readonly, and
typeset commands.
In POSIX mode, normal argument expansion is
done; in nonPOSIX
mode, field splitting, file globbing, brace expansion, and
(normal) tilde expansion are turned off, while assignment tilde expansion
is turned on.
+o Signal specification. In POSIX mode, signals can be
specified as
digits, only if signal numbers match POSIX values (i.e.,
HUP=1,
INT=2, QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15); in
non-POSIX
mode, signals can always be digits.
+o Alias expansion. In POSIX mode, alias expansion is only
carried out
when reading command words; in non-POSIX mode, alias expansion is
carried out on any word following an alias that ended in
a space.
For example, the following for loop
alias a='for ' i='j'
a i in 1 2; do echo i=$i j=$j; done
uses parameter i in POSIX mode, j in non-POSIX mode.
+o 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 [Toc] [Back]
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, and 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 the
set command
below), some special commands are very special in that no
field splitting,
file globbing, 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
., :, break, continue, eval, exec, exit, export, readonly,
return, set,
shift, trap, unset
Additional ksh special commands
builtin, times, typeset
Very special commands (non-POSIX)
alias, readonly, set, typeset
POSIX regular commands
alias, bg, cd, command, false, fc, fg, getopts, jobs, kill,
read, true,
umask, unalias, wait
Additional ksh regular commands
[, echo, let, print, pwd, test, ulimit, 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] [+-] [name[=value] ...]
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 effect).
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 option causes directory aliases, which are
used in tilde
expansion, to be l
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