- NAME
- SIMPLE COMMANDS & PIPELINES
- PRECOMMAND MODIFIERS
- COMPLEX COMMANDS
- ALTERNATE FORMS FOR COMPLEX COMMANDS
- RESERVED WORDS
- COMMENTS
- ALIASING
- QUOTING
- REDIRECTION
- MULTIOS
- REDIRECTIONS WITH NO COMMAND
- COMMAND EXECUTION
- FUNCTIONS
- AUTOLOADING FUNCTIONS
- SPECIAL FUNCTIONS
- JOBS
- SIGNALS
- ARITHMETIC EVALUATION
- CONDITIONAL EXPRESSIONS
- PROMPT EXPANSION
zshmisc
NAME
zshmisc - everything and then some
SIMPLE COMMANDS & PIPELINES
A simple command is a sequence of optional parameter
assignments followed by blank-separated words,
with optional redirections interspersed.
The first word is the command to be executed, and the remaining
words, if any, are arguments to the command.
If a command name is given, the parameter assignments modify
the environment of the command when it is executed.
The value of a simple command is its exit status,
or 128 plus the signal number if terminated by a signal.
For example,
echo foo
is a simple command with arguments.
A pipeline is either a simple command, or a sequence of two or more
simple commands where each command is separated from the next by `|'
or `|&'. Where commands are separated by `|', the standard
output of the first command is connected to the
standard input of the next. `|&' is shorthand for `2>&1 |', which
connects both the standard output and the standard error of the
command to the standard input of the next. The value of a pipeline
is the value of the last command, unless the pipeline is preceded by
`!' in which case the value is the logical inverse of the value of the
last command.
For example,
echo foo | sed 's/foo/bar/'
is a pipeline, where the output (`foo' plus a newline) of the first
command will be passed to the input of the second.
If a pipeline is preceded by `coproc', it is executed as a coprocess;
a two-way pipe is established between it and the parent shell. The
shell can read from or write to the coprocess by means of the `>&p'
and `<&p' redirection operators or with `print -p' and `read -p'.
A pipeline cannot be preceded by both `coproc' and `!'.
If job control is active, the coprocess can be treated in other than input
and output as an ordinary background job.
A sublist is either a single pipeline, or a sequence of two or more
pipelines separated by `&&' or `||'. If two pipelines are separated
by `&&', the second pipeline is executed only if the first succeeds
(returns a zero status). If two pipelines are separated by `||', the
second is executed only if the first fails (returns a nonzero status).
Both operators have equal precedence and are left associative.
The value of the sublist is the value of the last pipeline executed.
For example,
dmesg | grep panic && print yes
is a sublist consisting of two pipelines, the second just a simple command
which will be executed if and only if the grep command returns a zero
status. If it does not, the value of the sublist is that return status, else
it is the status returned by the print (almost certainly zero).
A list is a sequence of zero or more sublists, in which each sublist
is terminated by `;', `&', `&|', `&!', or a newline.
This terminator
may optionally be omitted from the last sublist in the list when the
list appears as a complex command inside `(...)'
or `{...}'. When a
sublist is terminated by `;' or newline, the shell waits for it to
finish before executing the next sublist. If a sublist is terminated
by a `&', `&|', or `&!',
the shell executes the last pipeline in it in the background, and
does not wait for it to finish (note the difference from other shells
which execute the whole sublist in the background).
A backgrounded pipeline returns a status of zero.
More generally, a list can be seen as a set of any shell commands
whatsoever, including the complex commands below; this is implied wherever
the word `list' appears in later descriptions. For example, the commands
in a shell function form a special sort of list.
PRECOMMAND MODIFIERS
A simple command may be preceded by a precommand modifier,
which will alter how the command is interpreted. These modifiers are
shell builtin commands with the exception of nocorrect which is
a reserved word.
-
The command is executed with a `-' prepended to its
argv[0] string.
noglob
Filename generation (globbing) is not performed on any of
the words.
nocorrect
Spelling correction is not done on any of the words. This must appear
before any other precommand modifier, as it is interpreted immediately,
before any parsing is done. It has no effect in non-interactive shells.
exec
The command is executed in the parent shell without forking.
command
The command word is taken to be the name of an external command,
rather than a shell function or builtin.
builtin
The command word is taken to be the name of a builtin command,
rather than a shell function or external command.
COMPLEX COMMANDS
A complex command in zsh is one of the following:
if list then list [ elif list then list ] ... [ else list ] fi
The if list is executed, and if it returns a zero exit status,
the then list is executed.
Otherwise, the elif list is executed and if its status is zero,
the then list is executed.
If each elif list returns nonzero status, the else list
is executed.
for name ... [ in word ... ] term do list done
where term is at least one newline or ;.
Expand the list of words, and set the parameter
name to each of them in turn, executing
list each time. If the in word is omitted,
use the positional parameters instead of the words.
More than one parameter name can appear before the list of
words. If N names are given, then on each execution of the
loop the next N words are assigned to the corresponding
parameters. If there are more names than remaining words, the
remaining parameters are each set to the empty string. Execution of the
loop ends when there is no remaining word to assign to the first
name. It is only possible for in to appear as the first name
in the list, else it will be treated as marking the end of the list.
for (( [expr1] ; [expr2] ; [expr3] )) do list done
The arithmetic expression expr1 is evaluated first (see
the section `Arithmetic Evaluation'). The arithmetic expression
expr2 is repeatedly evaluated until it evaluates to zero and
when non-zero, list is executed and the arithmetic expression
expr3 evaluated. If any expression is omitted, then it behaves
as if it evaluated to 1.
while list do list done
Execute the do list as long as the while list
returns a zero exit status.
until list do list done
Execute the do list as long as until list
returns a nonzero exit status.
repeat word do list done
word is expanded and treated as an arithmetic expression,
which must evaluate to a number n.
list is then executed n times.
case word in [ [(] pattern [ | pattern ] ... ) list (;;|;&|;|) ] ... esac
Execute the list associated with the first pattern
that matches word, if any. The form of the patterns
is the same as that used for filename generation. See
the section `Filename Generation'.
If the list that is executed is terminated with ;& rather than
;;, the following list is also executed. The rule for
the terminator of the following list ;;, ;& or ;| is
applied unless the esac is reached.
If the list that is executed is terminated with ;| the
shell continues to scan the patterns looking for the next match,
executing the corresponding list, and applying the rule for
the corresponding terminator ;;, ;& or ;|.
Note that word is not re-expanded; all applicable patterns
are tested with the same word.
select name [ in word ... term ] do list done
where term is one or more newline or ; to terminate the words.
Print the set of words, each preceded by a number.
If the in word is omitted, use the positional parameters.
The PROMPT3 prompt is printed and a line is read from the line editor
if the shell is interactive and that is active, or else standard input.
If this line consists of the
number of one of the listed words, then the parameter name
is set to the word corresponding to this number.
If this line is empty, the selection list is printed again.
Otherwise, the value of the parameter name is set to null.
The contents of the line read from standard input is saved
in the parameter REPLY. list is executed
for each selection until a break or end-of-file is encountered.
( list )
Execute list in a subshell. Traps set by the trap builtin
are reset to their default values while executing list.
{ list }
Execute list.
{ try-list } always { always-list }
First execute try-list. Regardless of errors, or break,
continue, or return commands encountered within try-list,
execute always-list. Execution then continues from the
result of the execution of try-list; in other words, any error,
or break, continue, or return command is treated in the
normal way, as if always-list were not present. The two
chunks of code are referred to as the `try block' and the `always block'.
Optional newlines or semicolons may appear after the always;
note, however, that they may not appear between the preceeding
closing brace and the always.
An `error' in this context is a condition such as a syntax error which
causes the shell to abort execution of the current function, script, or
list. Syntax errors encountered while the shell is parsing the
code do not cause the always-list to be executed. For example,
an erroneously constructed if block in try-list would cause the
shell to abort during parsing, so that always-list would not be
executed, while an erroneous substitution such as ${*foo*} would
cause a run-time error, after which always-list would be executed.
An error condition can be tested and reset with the special integer
variable TRY_BLOCK_ERROR. Outside an always-list the value is
irrelevant, but it is initialised to -1. Inside always-list, the
value is 1 if an error occurred in the try-list, else 0. If
TRY_BLOCK_ERROR is set to 0 during the always-list, the error
condition caused by the try-list is reset, and shell execution
continues normally after the end of always-list. Altering the value
during the try-list is not useful (unless this forms part of an
enclosing always block).
Regardless of TRY_BLOCK_ERROR, after the end of always-list the
normal shell status $? is the value returned from always-list.
This will be non-zero if there was an error, even if TRY_BLOCK_ERROR
was set to zero.
The following executes the given code, ignoring any errors it causes.
This is an alternative to the usual convention of protecting code by
executing it in a subshell.
{
# code which may cause an error
} always {
# This code is executed regardless of the error.
(( TRY_BLOCK_ERROR = 0 ))
}
# The error condition has been reset.
An exit command (or a return command executed at the outermost
function level of a script) encountered in try-list does not cause
the execution of always-list. Instead, the shell exits immediately
after any EXIT trap has been executed.
function word ... [ () ] [ term ] { list }
word ... () [ term ] { list }
word ... () [ term ] command
where term is one or more newline or ;.
Define a function which is referenced by any one of word.
Normally, only one word is provided; multiple words
are usually only useful for setting traps.
The body of the function is the list between
the { and }. See the section `Functions'.
If the option SH_GLOB is set for compatibility with other shells, then
whitespace may appear between between the left and right parentheses when
there is a single word; otherwise, the parentheses will be treated as
forming a globbing pattern in that case.
time [ pipeline ]
The pipeline is executed, and timing statistics are
reported on the standard error in the form specified
by the TIMEFMT parameter.
If pipeline is omitted, print statistics about the
shell process and its children.
[[ exp ]]
Evaluates the conditional expression exp
and return a zero exit status if it is true.
See the section `Conditional Expressions'
for a description of exp.
ALTERNATE FORMS FOR COMPLEX COMMANDS
Many of zsh's complex commands have alternate forms. These particular
versions of complex commands should be considered deprecated and may be
removed in the future. The versions in the previous section should be
preferred instead.
The short versions below only work if sublist is of the form `{
list }' or if the SHORT_LOOPS option is set. For the if,
while and until commands, in both these cases the test part of the
loop must also be suitably delimited, such as by `[[ ... ]]' or `((
... ))', else the end of the test will not be recognized. For the
for, repeat, case and select commands no such special form
for the arguments is necessary, but the other condition (the special form
of sublist or use of the SHORT_LOOPS option) still applies.
if list { list } [ elif list { list } ] ... [ else { list } ]
An alternate form of if. The rules mean that
if [[ -o ignorebraces ]] {
print yes
}
works, but
if true { # Does not work!
print yes
}
does not, since the test is not suitably delimited.
if list sublist
A short form of the alternate `if'. The same limitations on the form of
list apply as for the previous form.
for name ... ( word ... ) sublist
A short form of for.
for name ... [ in word ... ] term sublist
where term is at least one newline or ;.
Another short form of for.
for (( [expr1] ; [expr2] ; [expr3] )) sublist
A short form of the arithmetic for command.
foreach name ... ( word ... ) list end
Another form of for.
while list { list }
An alternative form of while. Note the limitations on the form of
list mentioned above.
until list { list }
An alternative form of until. Note the limitations on the form of
list mentioned above.
repeat word sublist
This is a short form of repeat.
case word { [ [(] pattern [ | pattern ] ... ) list (;;|;&|;|) ] ... }
An alternative form of case.
select name [ in word term ] sublist
where term is at least one newline or ;.
A short form of select.
RESERVED WORDS
The following words are recognized as reserved words when used as the first
word of a command unless quoted or disabled using disable -r:
do done esac then elif else fi for case
if while function repeat time until
select coproc nocorrect foreach end ! [[ { }
Additionally, `}' is recognized in any position if the IGNORE_BRACES option
is not set.
COMMENTS
In noninteractive shells, or in interactive shells with the
INTERACTIVE_COMMENTS option set, a word beginning
with the third character of the histchars parameter
(`#' by default) causes that word and all the following
characters up to a newline to be ignored.
ALIASING
Every token in the shell input is checked to see if there
is an alias defined for it.
If so, it is replaced by the text of the alias if it is in command
position (if it could be the first word of a simple command),
or if the alias is global.
If the text ends with a space, the next word in the shell input
is treated as though it were in command position for purposes of alias
expansion.
An alias is defined using the alias builtin; global aliases
may be defined using the -g option to that builtin.
Alias expansion is done on the shell input before any
other expansion except history expansion. Therefore,
if an alias is defined for the word foo, alias expansion
may be avoided by quoting part of the word, e.g. \foo.
But there is nothing to prevent an alias being defined
for \foo as well.
QUOTING
A character may be quoted (that is, made
to stand for itself) by preceding it with a `\'.
`\' followed by a newline is ignored.
A string enclosed between `$'' and `'' is
processed the same way as the string arguments of the
print builtin, and the resulting string is considered to be
entirely quoted. A literal `'' character can be included in the
string by using the `\'' escape.
All characters enclosed between a pair of single quotes ('') that
is not preceded by a `$' are quoted. A single quote cannot appear
within single quotes unless the option RC_QUOTES is set, in which case
a pair of single quotes are turned into a single quote. For example,
outputs nothing apart from a newline if RC_QUOTES is not set, but one
single quote if it is set.
Inside double quotes (""), parameter and
command substitution occur, and `\' quotes the characters
`\', ``', `"', and `$'.
REDIRECTION
If a command is followed by &
and job control is not active,
then the default standard input
for the command is the empty file /dev/null.
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by
input/output specifications.
The following may appear anywhere in a simple command
or may precede or follow a complex command.
Expansion occurs before word or digit
is used except as noted below.
If the result of substitution on word
produces more than one filename,
redirection occurs for each
separate filename in turn.
< word
Open file word for reading as standard input.
<> word
Open file word for reading and writing as standard input.
If the file does not exist then it is created.
> word
Open file word for writing as standard output.
If the file does not exist then it is created.
If the file exists, and the CLOBBER option is unset,
this causes an error;
otherwise, it is truncated to zero length.
>| word
>! word
Same as >, except that the file is truncated to zero length
if it exists, even if CLOBBER is unset.
>> word
Open file word for writing in append mode as standard output.
If the file does not exist, and the CLOBBER
option is unset, this causes an error;
otherwise, the file is created.
>>| word
>>! word
Same as >>, except that the file is created if it does not
exist, even if CLOBBER is unset.
<<[-] word
The shell input is read up to a line that is the same as
word, or to an end-of-file.
No parameter expansion, command substitution or
filename generation is performed on word.
The resulting document, called a
here-document, becomes the standard input.
If any character of word is quoted with
single or double quotes or a `\',
no interpretation is placed upon the characters of the document.
Otherwise, parameter and command substitution
occurs, `\' followed by a newline is removed,
and `\' must be used to quote the characters
`\', `$', ``' and the first character of word.
Note that word itself does not undergo shell expansion. Backquotes
in word do not have their usual effect; instead they behave
similarly to double quotes, except that the backquotes themselves are
passed through unchanged. (This information is given for completeness
and it is not recommended that backquotes be used.) Quotes in the form
$'...' have their standard effect of expanding backslashed
references to special characters.
If <<- is used, then all leading
tabs are stripped from word and from the document.
<<< word
Perform shell expansion on word and pass the result
to standard input. This is known as a here-string.
Compare the use of word in here-documents above, where word
does not undergo shell expansion.
<& number
>& number
The standard input/output is duplicated from file descriptor
number (see dup2(2)).
<& -
>& -
Close the standard input/output.
<& p
>& p
The input/output from/to the coprocess is moved to the standard input/output.
>& word
&> word
(Except where `>& word' matches one of the above syntaxes;
`&>' can always be used to avoid this ambiguity.)
Redirects both standard output and standard error (file descriptor 2)
in the manner of `> word'.
Note that this does not have the same effect as `> word 2>&1'
in the presence of multios (see the section below).
>&| word
>&! word
&>| word
&>! word
Redirects both standard output and standard error (file descriptor 2)
in the manner of `>| word'.
>>& word
&>> word
Redirects both standard output and standard error (file descriptor 2)
in the manner of `>> word'.
>>&| word
>>&! word
&>>| word
&>>! word
Redirects both standard output and standard error (file descriptor 2)
in the manner of `>>| word'.
If one of the above is preceded by a digit, then the file
descriptor referred to is that specified by the digit
instead of the default 0 or 1.
The order in which redirections are specified is significant.
The shell evaluates each redirection in terms of the
(file descriptor, file)
association at the time of evaluation.
For example:
... 1>fname 2>&1
first associates file descriptor 1 with file fname.
It then associates file descriptor 2 with the file associated with file
descriptor 1 (that is, fname).
If the order of redirections were reversed,
file descriptor 2 would be associated
with the terminal (assuming file descriptor 1 had been)
and then file descriptor 1 would be associated with file fname.
If instead of a digit one of the operators above is preceded by
a valid identifier enclosed in braces, the shell will open a new
file descriptor that is guaranteed to be at least 10 and set the
parameter named by the identifier to the file descriptor opened.
No whitespace is allowed between the closing brace and the redirection
character. The option IGNORE_BRACES must not be set.
For example:
... {myfd}>&1
This opens a new file descriptor that is a duplicate of file descriptor
1 and sets the parameter myfd to the number of the file descriptor,
which will be at least 10. The new file descriptor can be written to using
the syntax >&$myfd.
The syntax {varid}>&-, for example {myfd}>&-, may be used
to close a file descriptor opened in this fashion. Note that the
parameter given by varid must previously be set to a file descriptor
in this case.
It is an error to open or close a file descriptor in this fashion when the
parameter is readonly. However, it is not an error to read or write a file
descriptor using <&$param or >&$param if param is
readonly.
If the option CLOBBER is unset, it is an error to open a file
descriptor using a parameter that is already set to an open file descriptor
previously allocated by this mechanism. Unsetting the parameter before
using it for allocating a file descriptor avoids the error.
Note that this mechanism merely allocates or closes a file descriptor; it
does not perform any redirections from or to it. It is usually convenient
to allocate a file descriptor prior to use as an argument to exec. The
following shows a typical sequence of allocation, use, and closing of a
file descriptor:
integer myfd
exec {myfd}>~/logs/mylogfile.txt
print This is a log message. >&$myfd
exec {myfd}>&-
Note that the expansion of the variable in the expression >&$myfd
occurs at the point the redirection is opened. This is after the expansion
of command arguments and after any redirections to the left on the command
line have been processed.
The `|&' command separator described in
Simple Commands & Pipelines in zshmisc(1)
is a shorthand for `2>&1 |'.
The various forms of process substitution, `<(list)',
and `=(list())' for input and
`>(list)' for output, are often used together with
redirection. For example, if word in an output redirection is of the
form `>(list)' then the output is piped to the
command represented by list. See
Process Substitution in zshexpn(1).
MULTIOS
If the user tries to open a file descriptor for writing more than once,
the shell opens the file descriptor as a pipe to a process that copies
its input to all the specified outputs, similar to tee,
provided the MULTIOS option is set, as it is by default. Thus:
date >foo >bar
writes the date to two files, named `foo' and `bar'.
Note that a pipe is an implicit redirection; thus
date >foo | cat
writes the date to the file `foo', and also pipes it to cat.
If the MULTIOS
option is set, the word after a redirection operator is also subjected
to filename generation (globbing). Thus
: > *
will truncate all files in the current directory,
assuming there's at least one. (Without the MULTIOS
option, it would create an empty file called `*'.)
Similarly, you can do
echo exit 0 >> *.sh
If the user tries to open a file descriptor for reading more than once,
the shell opens the file descriptor as a pipe to a process that copies
all the specified inputs to its output in the order
specified, similar to cat,
provided the MULTIOS option is set. Thus
sort <foo <fubar
or even
sort <f{oo,ubar}
is equivalent to `cat foo fubar | sort'.
Expansion of the redirection argument occurs at the point the redirection
is opened, at the point described above for the expansion of the variable
in >&$myfd.
Note that a pipe is an implicit redirection; thus
cat bar | sort <foo
is equivalent to `cat bar foo | sort' (note the order of the inputs).
If the MULTIOS option is unset,
each redirection replaces the previous redirection for that file descriptor.
However, all files redirected to are actually opened, so
echo foo > bar > baz
when MULTIOS is unset will truncate bar, and write `foo' into baz.
There is a problem when an output multio is attached to an external
program. A simple example shows this:
cat file >file1 >file2 cat file1 file2
Here, it is possible that the second `cat' will not display the full
contents of file1 and file2 (i.e. the original contents of
file repeated twice).
The reason for this is that the multios are spawned after the cat
process is forked from the parent shell, so the parent shell does not
wait for the multios to finish writing data. This means the command as
shown can exit before file1 and file2 are completely written.
As a workaround, it is possible to run the cat process as part of a
job in the current shell:
{ cat file } >file >file2
Here, the {...} job will pause to wait for both files to be
written.
REDIRECTIONS WITH NO COMMAND
When a simple command consists of one or more redirection operators
and zero or more parameter assignments, but no command name, zsh can
behave in several ways.
If the parameter NULLCMD is not set or the option CSH_NULLCMD is
set, an error is caused. This is the csh behavior and CSH_NULLCMD
is set by default when emulating csh.
If the option SH_NULLCMD is set, the builtin `:' is inserted as a
command with the given redirections. This is the default when emulating
sh or ksh.
Otherwise, if the parameter NULLCMD is set, its value will be used as a
command with the given redirections. If both NULLCMD and
READNULLCMD are set, then the value of the latter will be used instead
of that of the former when the redirection is an input. The default for
NULLCMD is `cat' and for READNULLCMD is `more'. Thus
< file
shows the contents of file on standard output, with paging if that is a
terminal. NULLCMD and READNULLCMD may refer to shell functions.
COMMAND EXECUTION
If a command name contains no slashes, the shell attempts to locate
it. If there exists a shell function by that name, the function
is invoked as described in the section `Functions'. If there exists
a shell builtin by that name, the builtin is invoked.
Otherwise, the shell searches each element of $path for a
directory containing an executable file by that name. If the
search is unsuccessful, the shell prints an error message and returns
a nonzero exit status.
If execution fails because the file is not in executable format,
and the file is not a directory, it is assumed to be a shell
script. /bin/sh is spawned to execute it. If the program
is a file beginning with `#!', the remainder of the first line
specifies an interpreter for the program. The shell will
execute the specified interpreter on operating systems that do
not handle this executable format in the kernel.
FUNCTIONS
Shell functions are defined with the function reserved word or the
special syntax `funcname ()'.
Shell functions are read in and stored internally.
Alias names are resolved when the function is read.
Functions are executed like commands with the arguments
passed as positional parameters.
(See the section `Command Execution'.)
Functions execute in the same process as the caller and
share all files
and present working directory with the
caller. A trap on EXIT set inside a function
is executed after the function completes in the environment
of the caller.
The return builtin is used to return from function calls.
Function identifiers can be listed with the functions builtin.
Functions can be undefined with the unfunction builtin.
AUTOLOADING FUNCTIONS
A function can be marked as undefined using the autoload builtin
(or `functions -u' or `typeset -fu'). Such a function has no
body. When the function is first executed, the shell searches for its
definition using the elements of the fpath variable. Thus to define
functions for autoloading, a typical sequence is:
fpath=(~/myfuncs $fpath) autoload myfunc1 myfunc2 ...
The usual alias expansion during reading will be suppressed if the
autoload builtin or its equivalent is given the option -U. This is
recommended for the use of functions supplied with the zsh distribution.
Note that for functions precompiled with the zcompile builtin command
the flag -U must be provided when the .zwc file is created, as the
corresponding information is compiled into the latter.
For each element in fpath, the shell looks for three possible
files, the newest of which is used to load the definition for the function:
element.zwc
A file created with the zcompile builtin command, which is expected to
contain the definitions for all functions in the directory named
element. The file is treated in the same manner as a directory
containing files for functions and is searched for the definition of the
function. If the definition is not found, the search for a definition
proceeds with the other two possibilities described below.
If element already includes a .zwc extension (i.e. the extension
was explicitly given by the user), element is searched for the
definition of the function without comparing its age to that of other
files; in fact, there does not need to be any directory named element
without the suffix. Thus including an element such as
`/usr/local/funcs.zwc' in fpath will speed up the search for
functions, with the disadvantage that functions included must be explicitly
recompiled by hand before the shell notices any changes.
element/function.zwc
A file created with zcompile, which is expected to contain the
definition for function. It may include other function definitions
as well, but those are neither loaded nor executed; a file found in this
way is searched only for the definition of function.
element/function
A file of zsh command text, taken to be the definition for function.
In summary, the order of searching is, first, in the parents of
directories in fpath for the newer of either a compiled directory or
a directory in fpath; second, if more than one of these contains a
definition for the function that is sought, the leftmost in the fpath
is chosen; and third, within a directory, the newer of either a compiled
function or an ordinary function definition is used.
If the KSH_AUTOLOAD option is set, or the file contains only a
simple definition of the function, the file's contents will be executed.
This will normally define the function in question, but may also perform
initialization, which is executed in the context of the function execution,
and may therefore define local parameters. It is an error if the function
is not defined by loading the file.
Otherwise, the function body (with no surrounding `funcname()
{...}') is taken to be the complete contents of the file. This
form allows the file to be used directly as an executable shell script. If
processing of the file results in the function being re-defined, the
function itself is not re-executed. To force the shell to perform
initialization and then call the function defined, the file should contain
initialization code (which will be executed then discarded) in addition to
a complete function definition (which will be retained for subsequent calls
to the function), and a call to the shell function, including any
arguments, at the end.
For example, suppose the autoload file func contains
func() { print This is func; }
print func is initialized
then `func; func' with KSH_AUTOLOAD set will produce both messages
on the first call, but only the message `This is func' on the second
and subsequent calls. Without KSH_AUTOLOAD set, it will produce
the initialization message on the first call, and the other message on the
second and subsequent calls.
It is also possible to create a function that is not marked as autoloaded,
but which loads its own definition by searching fpath, by using
`autoload -X' within a shell function. For example, the following are
equivalent:
myfunc() {
autoload -X
}
myfunc args...
and
unfunction myfunc # if myfunc was defined autoload myfunc myfunc args...
In fact, the functions command outputs `builtin autoload -X' as
the body of an autoloaded function. This is done so that
eval "$(functions)"
produces a reasonable result. A true autoloaded function can be
identified by the presence of the comment `# undefined' in the body,
because all comments are discarded from defined functions.
To load the definition of an autoloaded function myfunc without
executing myfunc, use:
autoload +X myfunc
SPECIAL FUNCTIONS
Certain functions, if defined, have special meaning to the shell.
In the case of chpwd, periodic, precmd and preexec it is
possible to define an array that has the same name with `_functions'
appended. Any element in such an array is taken as the name of a function
to execute; it is executed in the same context and with the same arguments
as the basic function. For example, if $chpwd_functions is an array
containing the values `mychpwd', `chpwd_save_dirstack', then the
shell attempts to execute the functions `chpwd', `mychpwd' and
`chpwd_save_dirstack', in that order. Any function that does not exist
is silently ignored. A function found by this mechanism is referred to
elsewhere as a `hook function'. An error in any function causes
subsequent functions not to be run. Note further that an error
in a precmd hook causes an immediately following periodic
function not to run (thought it may run at the next opportunity).
chpwd
Executed whenever the current working directory is changed.
periodic
If the parameter PERIOD
is set, this function is executed every $PERIOD
seconds, just before a prompt. Note that if multiple functions
are defined using the array periodic_functions only one
period is applied to the complete set of functions, and the
scheduled time is not reset if the list of functions is altered.
Hence the set of functions is always called together.
precmd
Executed before each prompt.
preexec
Executed just after a command has been read and is about to be
executed. If the history mechanism is active (and the line was not
discarded from the history buffer), the string that the user typed is
passed as the first argument, otherwise it is an empty string. The
actual command that will be executed (including expanded aliases) is
passed in two different forms: the second argument is a single-line,
size-limited version of the command (with things like function bodies
elided); the third argument contains the full text that is being
executed.
zshexit
Executed at the point where the main shell is about to exit normally.
This is not called by exiting subshells, nor when the exec
precommand modifier is used before an external command. Also, unlike
TRAPEXIT, it is not called when functions exit.
TRAPNAL
If defined and non-null,
this function will be executed whenever the shell
catches a signal SIGNAL, where NAL is a signal
name as specified for the kill builtin.
The signal number will be passed as the first parameter to the function.
If a function of this form is defined and null,
the shell and processes spawned by it will ignore SIGNAL.
The return status from the function is handled specially. If it is
zero, the signal is assumed to have been handled, and execution continues
normally. Otherwise, the shell will behave as interrupted except that
the return status of the trap is retained.
Programs terminated by uncaught signals typically return the status 128
plus the signal number. Hence the following causes the handler for
SIGINT to print a message, then mimic the usual effect of the signal.
TRAPINT() {
print "Caught SIGINT, aborting."
return $(( 128 + $1 ))
}
The functions TRAPZERR, TRAPDEBUG and TRAPEXIT are never
executed inside other traps.
TRAPDEBUG
Executed after each command.
TRAPEXIT
Executed when the shell exits,
or when the current function exits if defined inside a function.
The value of $? at the start of execution is the exit status of the
shell or the return status of the function exiting.
TRAPZERR
Executed whenever a command has a non-zero exit status. However, the
function is not executed if the command occurred in a sublist followed by
`&&' or `||'; only the final command in a sublist of this type
causes the trap to be executed. The function TRAPERR acts the same as
TRAPZERR on systems where there is no SIGERR (this is the usual
case).
The functions beginning `TRAP' may alternatively be defined with the
trap builtin: this may be preferable for some uses, as they are then
run in the environment of the calling process, rather than in their own
function environment. Apart from the difference in calling procedure and
the fact that the function form appears in lists of functions, the forms
TRAPNAL() {
# code
}
and
trap ' # code ' NAL
are equivalent.
JOBS
If the MONITOR option is set,
an interactive shell associates a job with each pipeline.
It keeps a table of current jobs, printed by the jobs
command, and assigns them small integer numbers.
When a job is started asynchronously with `&',
the shell prints a line to standard error which looks like:
[1] 1234
indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process ID was 1234.
If a job is started with `&|' or `&!',
then that job is immediately disowned. After startup, it
does not have a place in the job table, and is not subject
to the job control features described here.
If you are running a job and wish to do something else you may hit the key
^Z (control-Z) which sends a TSTP signal to the current job: this key
may be redefined by the susp option of the external stty command.
The shell will then normally indicate that the job has been `suspended',
and print another prompt. You can then manipulate the state of this job,
putting it in the background with the bg command, or run some other
commands and then eventually bring the job back into the foreground with
the foreground command fg. A ^Z takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.
A job being run in the background will suspend if it tries to read
from the terminal.
Background jobs are normally allowed to produce output,
but this can be disabled by giving the command `stty tostop'.
If you set this
tty option, then background jobs will suspend when they try to produce
output like they do when they try to read input.
When a command is suspended and continued later with the fg or
wait builtins, zsh restores tty modes that were in effect when it was
suspended. This (intentionally) does not apply if the command is
continued via `kill -CONT', nor when it is continued with bg.
There are several ways to refer to jobs in the shell.
A job can be referred to by the process ID of any process of the job
or by one of the following:
%number
The job with the given number.
%string
Any job whose command line begins with string.
%?string
Any job whose command line contains string.
%%
Current job.
%+
Equivalent to `%%'.
%-
Previous job.
The shell learns immediately whenever a process changes state.
It normally informs you whenever a job becomes blocked so that
no further progress is possible. If the NOTIFY option is not set,
it waits until just before it prints a prompt before it informs you.
All such notifications are sent directly to the terminal, not to
the standard output or standard error.
When the monitor mode is on, each background job that completes
triggers any trap set for CHLD.
When you try to leave the shell while jobs are running or suspended, you will
be warned that `You have suspended (running) jobs'.
You may use the jobs command to see what they are.
If you do this or immediately try to
exit again, the shell will not warn you a second time; the suspended
jobs will be terminated, and the running jobs will be sent
a SIGHUP signal, if the HUP option is set.
To avoid having the shell terminate the running jobs, either
use the nohup command (see nohup(1))
or the disown builtin.
SIGNALS
The INT and QUIT signals for an invoked
command are ignored if the command is followed by
`&' and the MONITOR option is not active.
The shell itself always ignores the QUIT signal.
Otherwise, signals have the values
inherited by the shell from its parent
(but see the TRAPNAL special functions in the section `Functions').
ARITHMETIC EVALUATION
The shell can perform integer and floating point arithmetic, either using
the builtin let, or via a substitution of the form $((...)). For
integers, the shell is usually compiled to use 8-byte precision where this
is available, otherwise precision is 4 bytes. This can be tested, for
example, by giving the command `print - $(( 12345678901 ))'; if the
number appears unchanged, the precision is at least 8 bytes. Floating
point arithmetic is always double precision.
The let builtin command takes arithmetic expressions as arguments; each
is evaluated separately. Since many of the arithmetic operators, as well
as spaces, require quoting, an alternative form is provided: for any
command which begins with a `((', all the characters until a
matching `))' are treated as a quoted expression and
arithmetic expansion performed as for an argument of let. More
precisely, `((...))' is equivalent to
`let "..."'. The return status is 0 if the arithmetic value
of the expression is non-zero, and 1 otherwise.
For example, the following statement
(( val = 2 + 1 ))
is equivalent to
let "val = 2 + 1"
both assigning the value 3 to the shell variable val and returning a
zero status.
Integers can be in bases other than 10.
A leading `0x' or `0X' denotes hexadecimal.
Integers may also be of the form `base#n',
where base is a decimal number between two and thirty-six
representing the arithmetic base and n
is a number in that base (for example, `16#ff' is 255 in hexadecimal).
The base# may also be omitted, in which case
base 10 is used. For backwards compatibility the form
`[base]n' is also accepted.
It is also possible to specify a base to be used for output in the form
`[#base]', for example `[#16]'. This is used when
outputting arithmetical substitutions or when assigning to scalar
parameters, but an explicitly defined integer or floating point parameter
will not be affected. If an integer variable is implicitly defined by an
arithmetic expression, any base specified in this way will be set as the
variable's output arithmetic base as if the option `-i base' to
the typeset builtin had been used. The expression has no precedence
and if it occurs more than once in a mathematical expression, the last
encountered is used. For clarity it is recommended that it appear at the
beginning of an expression. As an example:
typeset -i 16 y print $(( [#8] x = 32, y = 32 )) print $x $y
outputs first `8#40', the rightmost value in the given output base, and
then `8#40 16#20', because y has been explicitly declared to
have output base 16, while x (assuming it does not already exist) is
implicitly typed by the arithmetic evaluation, where it acquires the output
base 8.
If the C_BASES option is set, hexadecimal numbers in the standard C
format, for example 0xFF instead of the usual `16#FF'. If the
option OCTAL_ZEROES is also set (it is not by default), octal numbers
will be treated similarly and hence appear as `077' instead of
`8#77'. This option has no effect on the output of bases other than
hexadecimal and octal, and these formats are always understood on input.
When an output base is specified using the `[#base]' syntax,
an appropriate base prefix will be output if necessary, so that the value
output is valid syntax for input. If the # is doubled, for example
`[##16]', then no base prefix is output.
Floating point constants are recognized by the presence of a decimal point
or an exponent. The decimal point may be the first character of the
constant, but the exponent character e or E may not, as it will be
taken for a parameter name.
An arithmetic expression uses nearly the same syntax, precedence, and
associativity of expressions in C.
The following operators are supported (listed in decreasing order
of precedence):
+ - ! ~ ++ --
unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement
<< >>
bitwise shift left, right
&
bitwise AND
^
bitwise XOR
|
bitwise OR
**
exponentiation
* / %
multiplication, division, modulus (remainder)
+ -
addition, subtraction
< > <= >=
comparison
== !=
equality and inequality
&&
logical AND
|| ^^
logical OR, XOR
? :
ternary operator
= += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
assignment
,
comma operator
The operators `&&', `||', `&&=', and `||=' are
short-circuiting, and only one of the latter two expressions in a ternary
operator is evaluated. Note the precedence of the bitwise AND, OR,
and XOR operators.
Mathematical functions can be called with the syntax
`func(args)', where the function decides
if the args is used as a string or a comma-separated list of
arithmetic expressions. The shell currently defines no mathematical
functions by default, but the module zsh/mathfunc may be loaded with
the zmodload builtin to provide standard floating point mathematical
functions.
An expression of the form `##x' where x is any character
sequence such as `a', `^A', or `\M-\C-x' gives the value of
this character and an expression of the form `#foo' gives the
value of the first character of the contents of the parameter foo.
Character values are according to the character set used in the current
locale; for multibyte character handling the option MULTIBYTE must be
set. Note that this form is different from `$#foo', a standard
parameter substitution which gives the length of the parameter foo.
`#\' is accepted instead of `##', but its use is deprecated.
Named parameters and subscripted arrays can be referenced by name within an
arithmetic expression without using the parameter expansion syntax. For
example,
((val2 = val1 * 2))
assigns twice the value of $val1 to the parameter named val2.
An internal integer representation of a named parameter
can be specified with the integer builtin.
Arithmetic evaluation is performed on the value of each
assignment to a named parameter declared integer
in this manner. Assigning a floating point number to an integer results in
rounding down to the next integer.
Likewise, floating point numbers can be declared with the float
builtin; there are two types, differing only in their output format, as
described for the typeset builtin. The output format can be bypassed
by using arithmetic substitution instead of the parameter substitution,
i.e. `${float}' uses the defined format, but
`$((float))' uses a generic floating point
format.
Promotion of integer to floating point values is performed where
necessary. In addition, if any operator which requires an integer
(`~', `&', `|', `^', `%', `<<', `>>' and their
equivalents with assignment) is given a floating point argument, it will be
silently rounded down to the next integer.
Scalar variables can hold integer or floating point values at different
times; there is no memory of the numeric type in this case.
If a variable is first assigned in a numeric context without previously
being declared, it will be implicitly typed as integer or float and
retain that type either until the type is explicitly changed or until the
end of the scope. This can have unforeseen consequences. For example, in
the loop
for (( f = 0; f < 1; f += 0.1 )); do # use $f done
if f has not already been declared, the first assignment will cause it
to be created as an integer, and consequently the operation `f += 0.1'
will always cause the result to be truncated to zero, so that the loop will
fail. A simple fix would be to turn the initialization into `f = 0.0'.
It is therefore best to declare numeric variables with explicit types.
CONDITIONAL EXPRESSIONS
A conditional expression is used with the [[
compound command to test attributes of files and to compare strings.
Each expression can be constructed from one or more
of the following unary or binary expressions:
-a file
true if file exists.
-b file
true if file exists and is a block special file.
-c file
true if file exists and is a character special file.
-d file
true if file exists and is a directory.
-e file
true if file exists.
-f file
true if file exists and is a regular file.
-g file
true if file exists and has its setgid bit set.
-h file
true if file exists and is a symbolic link.
-k file
true if file exists and has its sticky bit set.
-n string
true if length of string is non-zero.
-o option
true if option named option is on. option
may be a single character, in which case it is a single letter option name.
(See the section `Specifying Options'.)
-p file
true if file exists and is a FIFO special file (named pipe).
-r file
true if file exists and is readable by current process.
-s file
true if file exists and has size greater than zero.
-t fd
true if file descriptor number fd
is open and associated with a terminal device.
(note: fd is not optional)
-u file
true if file exists and has its setuid bit set.
-w file
true if file exists and is writable by current process.
-x file
true if file exists and is executable by current process.
If file exists and is a directory, then the current process
has permission to search in the directory.
-z string
true if length of string is zero.
-L file
true if file exists and is a symbolic link.
-O file
true if file exists and is owned by the effective user ID of this process.
-G file
true if file exists and its group matches
the effective group ID of this process.
-S file
true if file exists and is a socket.
-N file
true if file exists and its access time is
not newer than its modification time.
file1 -nt file2
true if file1 exists and is newer than file2.
file1 -ot file2
true if file1 exists and is older than file2.
file1 -ef file2
true if file1 and file2 exist and refer to the same file.
string = pattern
string == pattern
true if string matches pattern.
The `==' form is the preferred one. The `=' form is for
backward compatibility and should be considered obsolete.
string != pattern
true if string does not match pattern.
string1 < string2
true if string1 comes before string2
based on ASCII value of their characters.
string1 > string2
true if string1 comes after string2
based on ASCII value of their characters.
exp1 -eq exp2
true if exp1 is numerically equal to exp2.
exp1 -ne exp2
true if exp1 is numerically not equal to exp2.
exp1 -lt exp2
true if exp1 is numerically less than exp2.
exp1 -gt exp2
true if exp1 is numerically greater than exp2.
exp1 -le exp2
true if exp1 is numerically less than or equal to exp2.
exp1 -ge exp2
true if exp1 is numerically greater than or equal to exp2.
( exp )
true if exp is true.
! exp
true if exp is false.
exp1 && exp2
true if exp1 and exp2 are both true.
exp1 || exp2
true if either exp1 or exp2 is true.
Normal shell expansion is performed on the file, string and
pattern arguments, but the result of each expansion is constrained to
be a single word, similar to the effect of double quotes. However, pattern
metacharacters are active for the pattern arguments; the patterns
are the same as those used for filename generation, see
zshexpn(1), but there is no special behaviour
of `/' nor initial dots, and no glob qualifiers are allowed.
In each of the above expressions, if
file is of the form `/dev/fd/n',
where n is an integer,
then the test applied to the open file whose
descriptor number is n,
even if the underlying system does not support
the /dev/fd directory.
In the forms which do numeric comparison, the expressions exp
undergo arithmetic expansion as if they were enclosed in $((...)).
For example, the following:
[[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.
tests if either file foo or file bar exists, and if so, if the
value of the parameter report begins with `y'; if the complete
condition is true, the message `File exists.' is printed.
PROMPT EXPANSION
Prompt sequences undergo a special form of expansion. This type of expansion
is also available using the -P option to the print builtin.
If the PROMPT_SUBST option is set, the prompt string is first subjected to
parameter expansion,
command substitution and
arithmetic expansion.
See
zshexpn(1).
Certain escape sequences may be recognised in the prompt string.
If the PROMPT_BANG option is set, a `!' in the prompt is replaced
by the current history event number. A literal `!' may then be
represented as `!!'.
If the PROMPT_PERCENT option is set, certain escape sequences that
start with `%' are expanded.
Some escapes take an optional integer argument, which
should appear between the `%' and the next character of the
sequence. The following escape sequences are recognized:
%%
A `%'.
%)
A `)'.
%l
The line (tty) the user is logged in on, without `/dev/' prefix.
If the name starts with `/dev/tty', that prefix is stripped.
%M
The full machine hostname.
%m
The hostname up to the first `.'.
An integer may follow the `%' to specify
how many components of the hostname are desired. With a negative integer,
trailing components of the hostname are shown.
%n
$USERNAME.
%y
The line (tty) the user is logged in on, without `/dev/' prefix.
This does not treat `/dev/tty' names specially.
%#
A `#' if the shell is running with privileges, a `%' if not.
Equivalent to `%(!.#.%%)'.
The definition of `privileged', for these purposes, is that either the
effective user ID is zero, or, if POSIX.1e capabilities are supported, that
at least one capability is raised in either the Effective or Inheritable
capability vectors.
%?
The return status of the last command executed just before the prompt.
%_
The status of the parser, i.e. the shell constructs (like `if' and
`for') that have been started on the command line. If given an integer
number that many strings will be printed; zero or negative or no integer means
print as many as there are. This is most useful in prompts PS2 for
continuation lines and PS4 for debugging with the XTRACE option; in
the latter case it will also work non-interactively.
%d
%/
Present working directory ($PWD). If an integer follows the `%',
it specifies a number of trailing components of $PWD to show; zero
means the whole path. A negative integer specifies leading components,
i.e. %-1d specifies the first component.
%~
As %d and %/, but if $PWD has a named directory as its prefix,
that part is replaced by a `~' followed by the name of the directory.
If it starts with $HOME, that part is replaced by a `~'.
%h
%!
Current history event number.
%i
The line number currently being executed in the script, sourced file, or
shell function given by %N. This is most useful for debugging as part
of $PS4.
%j
The number of jobs.
%L
The current value of $SHLVL.
%N
The name of the script, sourced file, or shell function that zsh is
currently executing, whichever was started most recently. If there is
none, this is equivalent to the parameter $0. An integer may follow
the `%' to specify a number of trailing path components to show; zero
means the full path. A negative integer specifies leading components.
%c
%.
%C
Trailing component of $PWD.
An integer may follow the `%' to get more than one component.
Unless `%C' is used, tilde contraction is performed first. These are
deprecated as %c and %C are equivalent to %1~ and %1/,
respectively, while explicit positive integers have the same effect as for
the latter two sequences.
%D
The date in yy-mm-dd format.
%T
Current time of day, in 24-hour format.
%t
%@
Current time of day, in 12-hour, am/pm format.
%*
Current time of day in 24-hour format, with seconds.
%w
The date in day-dd format.
%W
The date in mm/dd/yy format.
%D{string}
string is formatted using the strftime function.
See strftime(3) for more details. Three additional codes are
available: %f prints the day of the month, like %e but
without any preceding space if the day is a single digit, and
%K/%L correspond to %k/%l for the hour of the day
(24/12 hour clock) in the same way.
%B (%b)
Start (stop) boldface mode.
%E
Clear to end of line.
%U (%u)
Start (stop) underline mode.
%S (%s)
Start (stop) standout mode.
%{...%}
Include a string as a literal escape sequence.
The string within the braces should not change the cursor
position. Brace pairs can nest.
%v
The value of the first element of the psvar array parameter. Following
the `%' with an integer gives that element of the array. Negative
integers count from the end of the array.
%(x.true-text.false-text)
Specifies a ternary expression. The character following the x is
arbitrary; the same character is used to separate the text for the
`true' result from that for the `false' result.
This separator may not appear in the true-text, except as part of a
%-escape
sequence. A `)' may appear in the false-text as `%)'.
true-text
and false-text may both contain arbitrarily-nested escape
sequences, including further ternary expressions.
The left parenthesis may be preceded or followed by a positive integer n,
which defaults to zero. A negative integer will be multiplied by -1.
The test character x may be any of the following:
!
True if the shell is running with privileges.
#
True if the effective uid of the current process is n.
?
True if the exit status of the last command was n.
_
True if at least n shell constructs were started.
C
/
True if the current absolute path has at least n elements
relative to the root directory, hence / is counted as 0 elements.
c
.
~
True if the current path, with prefix replacement, has at
least n elements relative to the root directory, hence / is
counted as 0 elements.
D
True if the month is equal to n (January = 0).
d
True if the day of the month is equal to n.
g
True if the effective gid of the current process is n.
j
True if the number of jobs is at least n.
L
True if the SHLVL parameter is at least n.
l
True if at least n characters have already been
printed on the current line.
S
True if the SECONDS parameter is at least n.
T
True if the time in hours is equal to n.
t
True if the time in minutes is equal to n.
v
True if the array psvar has at least n elements.
w
True if the day of the week is equal to n (Sunday = 0).
%<string<
%>string>
%[xstring]
Specifies truncation behaviour for the remainder of the prompt string.
The third, deprecated, form is equivalent to `%xstringx',
i.e. x may be `<' or `>'.
The numeric argument, which in the third form may appear immediately
after the `[', specifies the maximum permitted length of
the various strings that can be displayed in the prompt.
The string will be displayed in
place of the truncated portion of any string; note this does not
undergo prompt expansion.
The forms with `<' truncate at the left of the string,
and the forms with `>' truncate at the right of the string.
For example, if the current directory is `/home/pike',
the prompt `%8<..<%/' will expand to `..e/pike'.
In this string, the terminating character (`<', `>' or `]'),
or in fact any character, may be quoted by a preceding `\'; note
when using print -P, however, that this must be doubled as the
string is also subject to standard print processing, in addition
to any backslashes removed by a double quoted string: the worst case
is therefore `print -P "%<\\<<..."'.
If the string is longer than the specified truncation length,
it will appear in full, completely replacing the truncated string.
The part of the prompt string to be truncated runs to the end of the
string, or to the end of the next enclosing group of the `%('
construct, or to the next truncation encountered at the same grouping
level (i.e. truncations inside a `%(' are separate), which
ever comes first. In particular, a truncation with argument zero
(e.g. `%<<') marks the end of the range of the string to be
truncated while turning off truncation from there on. For example, the
prompt '%10<...<%~%<<%# ' will print a truncated representation of the
current directory, followed by a `%' or `#', followed by a
space. Without the `%<<', those two characters would be included
in the string to be truncated.
