zshmisc.man

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.\"
.TH ZSHMISC 1 "June 26, 1996" "zsh version 3.0"
.SH NAME
zshmisc \- Everything and then some
.SH SYNOPSIS
Everything I haven't put somewhere else
.SH "SHELL GRAMMAR"
A \fIsimple command\fP 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.
.PP
A \fIpipeline\fP is a sequence of one or more commands separated
by \fB|\fP or \fB|&\fP.  \fB|&\fP is shorthand for \fB2>&1 |\fP.
The standard output of each command is connected to the standard input
of the next command in the pipeline.  If a pipeline is preceded by
\fBcoproc\fP, 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 \fB>&p\fP and \fB<&p\fP redirection operators.
The value of a pipeline is the value of the last command.  If a pipeline
is preceded by a \fB!\fP, the value of that pipeline is the logical NOT
of the value of the last command.
.PP
A \fIsublist\fP is a sequence of one or more pipelines
separated by \fB&&\fP or \fB|\||\fP.  If two pipelines
are separated by \fB&&\fP, the second pipeline is executed
only if the first is successful (returns a zero value).
If two pipelines are separated by \fB|\||\fP, the second is executed
only if the first is unsuccessful (returns a nonzero value).  Both
operators have equal precedence and are left associative.
.PP
A \fIlist\fP is a sequence of zero or more sublists
separated by, and optionally terminated by, \fB;\fP, \fB&\fP, \fB&|\fP,
\fB&!\fP or a newline.
Normally the shell waits for each list to finish before executing
the next one.
If a list is terminated by \fB&\fP, \fB&|\fP or \fB&!\fP, the shell
executes it in the background, and does not wait for it to finish.
.SH "PRECOMMAND MODIFIERS"
A simple command may be preceded by a \fIprecommand\fP modifier
which will alter how the command is interpreted.  These modifiers are
shell builtin commands with the exception of \fBnocorrect\fP which is
a reserved word.
.PP
.PD 0
.TP
\fB\-
The command is executed with a \fB\-\fP prepended to its
\fBargv[0]\fP string.
.TP
\fBnoglob
Filename generation (globbing) is not performed on any of
the words.
.TP
\fBnocorrect
Spelling correction is not done on any of the words.
.TP
\fBexec
The command is executed in the parent shell without forking.
.TP
\fBcommand
The command word is taken to be the name of an external command,
rather than a shell function or builtin.

.SH "COMPLEX COMMANDS"
.PP
A \fIcomplex command\fP in zsh is one of the following:
.PD
.TP
\fBif\fP \fIlist\fP \fBthen\fP \fIlist\fP [ \fBelif\fP \fIlist\fP \fBthen\fP \fIlist\fP ] ... [ \fBelse\fP \fIlist\fP ] \fBfi\fP
The \fBif\fP \fIlist\fP is executed, and,
if it returns a zero exit status,
the \fBthen\fP \fIlist\fP is executed.
Otherwise, the \fBelif\fP \fIlist\fP is
executed and, if its value is zero,
the \fBthen\fP \fIlist\fP is executed.
If each \fBelif\fP \fIlist\fP returns
nonzero, the \fBelse\fP \fIlist\fP is executed.
.TP
\fBfor\fP \fIname\fP [ \fBin\fP \fIword\fP ... \fIterm\fP ] \fBdo\fP \fIlist\fP \fBdone\fP
where \fIterm\fP is one ore more newline or \fB;\fP.
Expand the list of \fIword\fPs, and set the parameter
\fIname\fP to each of them in turn, executing
\fIlist\fP each time.  If the \fBin\fP \fIword\fP is omitted,
use the positional parameters instead of the \fIword\fPs.
.TP
\fBwhile\fP \fIlist\fP \fBdo\fP \fIlist\fP \fBdone\fP
Execute the \fBdo\fP \fIlist\fP as long as the \fBwhile\fP \fIlist\fP
returns a zero exit status.
.TP
\fBuntil\fP \fIlist\fP \fBdo\fP \fIlist\fP \fBdone\fP
Execute the \fBdo\fP \fIlist\fP as long as \fBuntil\fP \fIlist\fP
returns a nonzero exit status.
.TP
\fBrepeat\fP \fIword\fP \fBdo\fP \fIlist\fP \fBdone\fP
\fIword\fP is expanded and treated as an arithmetic expression,
which must evaluate to a number \fIn\fP.
\fIlist\fP is then executed \fBn\fP times.
.TP
\fBcase\fP \fIword\fP \fBin\fP [ [\fB(\fP] \fIpattern\fP [ \fB|\fP \fIpattern\fP ] ... \fB)\fP \fIlist\fP \fB;;\fP ] ... \fBesac\fP
Execute the \fIlist\fP associated with the first \fIpattern\fP
that matches \fIword\fP, if any.  The form of the patterns
is the same as that used for filename generation.  See
\fIFilename Generation\fP below.
.TP
\fBselect\fP \fIname\fP [ \fBin\fP \fIword\fP ... \fIterm\fP ] \fBdo\fP \fIlist\fP \fBdone\fP
where \fIterm\fP is one ore more newline or \fB;\fP.
Print the set of \fIword\fPs, each preceded by a number.
If the \fBin\fP \fIword\fP is omitted, use the positional parameters.
The \fBPROMPT3\fP prompt is printed and a line is read from standard
input.  If this line consists of the number of one of the listed
\fIword\fPs, then the parameter \fIname\fP
is set to the \fIword\fP corresponding to this number.
If this line is empty, the selection list is printed again.
Otherwise, the value of the parameter \fIname\fP is set to null.
The contents of the line read from standard input is saved
in the parameter \fBREPLY\fP.  \fIlist\fP is executed
for each selection until a break or end-of-file is encountered.
.TP
\fB(\fP \fIlist\fP \fB)\fP
Execute \fIlist\fP in a subshell.  Traps set by the \fBtrap\fP builtin
are reset to their default values while executing \fIlist\fP.
.TP
\fB{\fP \fIlist\fP \fB}\fP
Execute \fIlist\fP.
.TP
.PD 0
\fBfunction\fP \fIword\fP ... [ \fB(\fP\|\fB)\fP ] [ \fIterm\fP ] \fB{\fP \fIlist\fP \fB}\fP
.TP
\fIword\fP ... \fB(\fP\|\fB)\fP [ \fIterm\fP ] \fB{\fP \fIlist\fP \fB}\fP
.TP
\fIword\fP ... \fB(\fP\|\fB)\fP [ \fIterm\fP ] \fIcommand\fP
.PD
where \fIterm\fP is one ore more newline or \fB;\fP.
Define a function which is referenced by any one of \fIword\fP.
Normally, only one \fIword\fP is provided; multiple \fIword\fPs
are usually only useful for setting traps.
The body of the function is the \fIlist\fP between
the \fB{\fP and \fB}\fP. See \fBFUNCTIONS\fP below.
.TP
\fBtime\fP [ \fIpipeline\fP ]
The \fIpipeline\fP is executed, and timing statistics are
reported on the standard error in the form specified
by the \fBTIMEFMT\fP parameter.
If \fIpipeline\fP is omitted, print statistics about the
shell process and its children.
.TP
\fB[[\fP \fIexp\fP \fB]]\fP
Evaluates the conditional expression \fIexp\fP
and return a zero exit status if it is true.
See \fBConditional Expressions\fP below for a description
of \fIexp\fP.
.SH "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 \fIsublist\fP
is of the form \fB{\fP \fIlist\fP \fB}\fP or if the \fBNO_SHORT_LOOPS\fP
option is not set.
.PP
.PD
.TP
\fBif\fP \fIlist\fP \fB{\fP \fIlist\fP \fB}\fP [ \fBelif\fP \fIlist\fP \fB{\fP \fIlist\fP \fB}\fP ] ... [ \fBelse {\fP \fIlist\fP \fB}\fP ]
An alternate form of \fBif\fP.
.TP
\fBif\fP \fIlist\fP \fIsublist\fP
A short form of previous one.
.TP
\fBfor\fP \fIname\fP \fB(\fP \fIword\fP ... \fB) \fIsublist\fP
A short form of \fBfor\fP.
.TP
\fBfor\fP \fIname\fP [ \fBin\fP \fIword\fP ... \fIterm\fP ] \fIsublist\fP
where \fIterm\fP is one ore more newline or \fB;\fP.
Another short form of \fBfor\fP.
.TP
\fBforeach\fP \fIname\fP \fB(\fP \fIword\fP ... \fB)\fP \fIlist\fP \fBend\fP
Another form of \fBfor\fP.
.TP
\fBwhile\fP \fIlist\fP \fB{\fP \fIlist\fP \fB}\fP
An alternative form of \fBwhile\fP.
.TP
\fBuntil\fP \fIlist\fP \fB{\fP \fIlist\fP \fB}\fP
An alternative form of \fBuntil\fP.
.TP
\fBrepeat\fP \fIword\fP \fIsublist\fP
This is a short form of \fBrepeat\fP.
.TP
\fBcase\fP \fIword\fP \fB{\fP [ [\fB(\fP] \fIpattern\fP [ \fB|\fP \fIpattern\fP ] ... \fB)\fP \fIlist\fP \fB;;\fP ] ... \fB}\fP
An alternative form of \fBcase\fP.
.TP
\fBselect\fP \fIname\fP [ \fBin\fP \fIword\fP \fIterm\fP ] \fIsublist\fP
where \fIterm\fP is one ore more newline or \fB;\fP.
A short form of \fBselect\fP.
.SH "RESERVED WORDS"
The following words are recognized as reserved words when used as the
first word of a command unless quoted or disabled using \fBdisable -r\fP:
.RS
.PP
\fBdo done esac then elif else fi for case
if while function repeat time until
select coproc nocorrect foreach end ! [[ { }\fP
.PP
Additionally \fB}\fP is recognized in any position if the
\fBIGNORE_BRACES\fP option is not set.
.RE
.SH COMMENTS
In noninteractive shells, or in interactive shells with the
\fBINTERACTIVE_COMMENTS\fP option set, a word beginning
with the third character of the \fBhistchars\fP parameter
(`#' by default) causes that word and all the following
characters up to a newline to be ignored.
.SH 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 \fBalias\fP builtin; global aliases
may be defined using the \-\fBg\fP option to that builtin.
.PP
Alias substitution is done on the shell input before any
other substitution except history substitution.  Therefore,
if an alias is defined for the word \fBfoo\fP, alias substitution
may be avoided by quoting part of the word, e.g. \fB\efoo\fP.
But there is nothing to prevent an alias being defined
for \fB\efoo\fP as well.
.SH QUOTING
A character may be \fIquoted\fP (that is, made
to stand for itself) by preceding it with a \e\|.
\e followed by a newline is ignored.
All characters enclosed between a pair of single quotes ('')
are quoted. A single quote cannot appear within single quotes.
Inside double quotes (""), parameter and command substitution
occurs, and \e quotes the characters \e\|, `, ", and $.
.SH REDIRECTION
Before a command is executed, its input and output
may be redirected.
The following may appear anywhere in a simple command
or may precede or follow a complex command.
Substitution occurs before
.I word
or
.I digit
is used except as noted below.
If the result of substitution on
.I word
produces more than one filename,
redirection occurs for each
separate filename in turn.
.TP
.BI < word
Open file
.I word
as standard input.
.TP
.BI <> word
Open file
.I word
for reading and writing as standard input.
If the file does not exist then it is created.
.TP
.BI > word
Open file
.I word
as standard output.
If the file does not exist then it is created.
If the file exists, and the
.B CLOBBER
option is unset,
this causes an error;
otherwise, it is truncated to zero length.
.TP
.PD 0
.BI >| " word"
.TP
.BI >! " word"
.PD
Same as
.BR > ,
except that the file is truncated to zero length
if it exists, even if
.B CLOBBER
is unset.
.TP
.BI >> word
Open file
.I word
as standard output.
If the file exists then output is appended to it.
If the file does not exist, and the
.B CLOBBER
option is unset,
this causes an error;
otherwise, the file is created.
.TP
.PD 0
.BI >>| " word"
.TP
.BI >>! " word"
.PD
Same as
.BR >> ,
except that the file is created if it does not
exist, even if
.B CLOBBER
is unset.
.TP
\fB<<\fP[\-] \fIword\fP
The shell input is read up to a line that is the same as
.IR word ,
or to an end-of-file.
No parameter substitution, command substitution or
filename generation is performed on
.IR word .
The resulting document,
called a
.IR here-document ,
becomes
the standard input.
If any character of \fIword\fP is quoted with
single or double quotes or a \e,
no interpretation
is placed upon the characters of the document.
Otherwise, parameter and command substitution
occurs, \e followed by a newline is removed,
and \e must be used to quote the characters
\e, $, `, and the first character of \fIword\fP.
If <<\- is used, then all leading
tabs are stripped from \fIword\fP and from the document.
.TP
.BI <<< word
Perform shell expansion on \fIword\fP and pass the result
to standard input.
.TP
.BI <& digit
The standard input
is duplicated from file descriptor
.I digit
(see
.IR dup (2)).
Similarly for standard output using
\fB>&\fIdigit\fP.
.TP
.BI >& word
Same as
.BI > word
\fB2>&\fP1.
.TP
.BI >>& word
Same as
.BI >> word
\fB2>&\fP1.
.TP
.BI <&\-
Close the standard input.
.TP
.BI >&\-
Close the standard output.
.TP
.BI <&p
The input from the coprocess is moved to the standard input.
.TP
.BI >&p
The output to the coprocess is moved to the standard output.
.PP
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
.RI ( "file descriptor" ", " file )
association at the time of evaluation.
For example:
.RS
.PP
\&.\|.\|. \|1>\fIfname\^\fP 2>&1
.RE
.PP
first associates file descriptor 1 with file
.IR fname .
It then associates file descriptor 2 with the file associated with file
descriptor 1 (that is,
.IR 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
.IR fname .
.PP
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(1),
provided the \fBMULTIOS\fP option is set.  Thus:
.RS
.PP
.B date >foo >bar
.RE
.PP
writes the date to two files, named "foo" and "bar".
Note that a pipe is an implicit indirection; thus
.RS
.PP
.B date >foo | cat
.RE
.PP
writes the date to the file "foo", and also pipes it to cat.
.PP
If the
.B MULTIOS
option is set, the word after a redirection operator is also subjected
to filename generation (globbing).  Thus
.RS
.PP
.B : > *
.RE
.PP
will truncate all files in the current directory,
assuming there's at least one.
(Without the
.B MULTIOS
option, it would create an empty file called "*".)
.PP
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(1),
provided the \fBMULTIOS\fP option is set.  Thus
.RS
.PP
.B sort <foo <fubar
.RE
.PP
or even
.RS
.PP
.B sort <f{oo,ubar}
.RE
.PP
is equivalent to "cat foo fubar | sort".  Similarly, you can do
.RS
.PP
.B echo exit 0 >> *.sh
.RE
.PP
Note that a pipe is in implicit indirection; thus
.RS
.PP
.B cat bar | sort <foo
.RE
.PP
is equivalent to "cat bar foo | sort" (note the order of the inputs).
.PP
If the
.B MULTIOS
option is
.IR un set,
each redirection replaces the previous redirection for that file descriptor.
However, all files redirected to are actually opened, so
.RS
.PP
.B echo foo > bar > baz
.RE
.PP
when
.B MULTIOS
is unset will truncate bar, and write "foo" into baz.
.PP
If a simple command consists of one or more redirection operators
and zero or more parameter assignments, but no command name,
the command \fBcat\fP is assumed.  Thus
.RS
.PP
.B < file
.RE
.PP
prints the contents of \fBfile\fP.
.PP
If a command is followed by
.B &
and job control is not active,
then the default standard input
for the command
is the empty file
.BR /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.
.SH "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 below in \fBFUNCTIONS\fP.  If there exists
a shell builtin by that name, the builtin is invoked.
.PP
Otherwise, the shell searches each element of \fBpath\fP 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.
.PP
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 \fB#!\fP, 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.
.SH FUNCTIONS
.PP
The
.B function
reserved word is used to define shell functions.
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
.I Execution
below).
.PP
Functions execute in the same process as the caller and
share all files
and present working directory with the
caller.
A trap on
.B EXIT
set inside a function
is executed after the function completes in the environment
of the caller.
.PP
The
.B return
builtin is used to return
from function calls.
.PP
Function identifiers
can be listed with the
.B functions
builtin.
Functions can be undefined with the
.B unfunction
builtin.
.PP
The following functions, if defined, have special meaning to
the shell:
.PP
.PD 0
.TP
\fBchpwd\fP
Executed whenever the current working directory is changed.
.TP
\fBprecmd\fP
Executed before each prompt.
.TP
\fBperiodic\fP
If the parameter
.B PERIOD
is set, this function is executed every
.B PERIOD
seconds, just before a prompt.
.TP
\fBTRAPxxx\fP
If defined and non-null,
this function will be executed whenever the shell
catches a signal \fBSIGxxx\fP, where \fBxxx\fP is a signal
name as specified for the \fBkill\fP builtin (see below).
The signal number will be passed as the first parameter to the function.
In addition, \fBTRAPZERR\fP is executed whenever a command has a non-zero
exit status, \fBTRAPDEBUG\fP is executed after each command, and
\fBTRAPEXIT\fP
is executed when the shell exits,
or when the current function exits if defined
inside a function.
If a function of this form is defined and null,
the shell and processes spawned by it will ignore \fBSIGxxx\fP.
.PD
.SH JOBS
.PP
If the
.B MONITOR
option is set,
an interactive shell associates a \fIjob\fR with each pipeline.
It keeps
a table of current jobs, printed by the
.B jobs
command, and assigns them small integer numbers.
When a job is started asynchronously with
.BR & ,
the shell prints a line which looks
like:
.PP
.DT
	[1] 1234
.PP
indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process id was 1234.
.PP
If a job is started with
.BR &|
or
.BR &! ,
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.
.PP
If you are running a job and wish to do something else you may hit the key
\fB^Z\fR (control-Z) which sends a TSTP signal to the current job.
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
.B bg
command, or run some other
commands and then eventually bring the job back into the foreground with
the foreground command
.BR fg .
A \fB^Z\fR takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.
.PP
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.
.PP
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:
.PD 0
.TP
.BI % number
The job with the given number.
.TP
.BI % string
Any job whose command line begins with
.IR string .
.TP
.BI %? string
Any job whose command line contains
.IR string .
.TP
.BI %%
Current job.
.TP
.BI %+
Equivalent to
.BR %% .
.TP
.BI %\-
Previous job.
.PD
.PP
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
.B notify
is not set, it waits until
just before it prints
a prompt before it informs you.
.PP
When the monitor mode is on, each background job that completes
triggers any trap set for
.BR CHLD .
.PP
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
.B 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 \fBSIGHUP\fP signal.
To avoid having the shell terminate the running jobs, either
use the \fBnohup\fP(1) command or the \fBdisown\fP builtin (see below).
.SH SIGNALS
The INT and QUIT signals for an invoked
command are ignored if the command is followed by
.B &
and the job
.B MONITOR
option is not active.
Otherwise, signals have the values
inherited by the shell from its parent
(but see the \fBTRAPxxx\fP special function above).
.SH "ARITHMETIC EVALUATION"
An ability to perform integer arithmetic
is provided with the builtin
.BR let .
Evaluations are performed using
.I long
arithmetic. A leading \fI0x\fP or \fI0X\fP denotes hexadecimal.
Otherwise, numbers are of the form
[\fIbase\fB#\^\fR]\fIn\^\fP
where
.I base
is a decimal number between two and thirty-six
representing the arithmetic base
and
.I n
is a number in that base (for example, `16#ff' is 255 in hexadecimal).
If
.I base
is omitted
then base 10 is used.  For backwards compatibility the form `[16]ff'
is also accepted.
.PP
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):
.PP
.PD 0
.RS
.TP
.B + \- ! \(ap ++ \-\|\-
unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement
.TP
.B << >>
bitwise shift left, right
.TP
.B &
bitwise AND
.TP
.B ^
bitwise XOR
.TP
.B |
bitwise OR
.TP
.B **
exponentiation
.TP
.B * / %
multiplication, division, modulus (remainder)
.TP
.B + \-
addition, subtraction
.TP
.B < > <= >=
comparison
.TP
.B == !=
equality and inequality
.TP
.B &&
logical AND
.TP
.B |\|| ^^
logical OR, XOR
.TP
.B ? :
ternary operator
.TP
.B
= += \-= *= /= %= &= ^= |= <<= >>= &&= |\||= ^^= **=
assignment
.TP
.B ,
comma operator
.PD
.RE
.PP
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.
.PP
An expression of the form \fB#\\x\fP where \fBx\fP is any character
gives the ascii value of this character and an expression of the form
\fB#foo\fP gives the ascii value of the first character of the value
of the parameter \fBfoo\fP.
.PP
Named parameters and subscripted arrays can be referenced by name within an
arithmetic expression without using the parameter substitution syntax.
.PP
An internal integer representation of a named parameter
can be specified with the
.B integer
builtin.
Arithmetic evaluation is performed on the value of each
assignment to a named parameter declared integer
in this manner.
.PP
Since many of the arithmetic operators require
quoting, an alternative form of the
.B let
command is provided.
For any command which begins with a
.BR (( ,
all the characters until a matching
.B ))
are treated as a quoted expression.
More precisely,
.BR (( ... ))
is equivalent to
.B let
\fB"\fP...\fB"\fP.
.SH "CONDITIONAL EXPRESSIONS"
A \fIconditional expression\fP is used with the
.B [[
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:
.PD 0
.TP
\fB\-a\fP \fIfile\fP
true if
.I file
exists.
.TP
\fB\-b\fP \fIfile\fP
true if
.I file
exists and is a block special file.
.TP
\fB\-c\fP \fIfile\fP
true if
.I file
exists and is a character special file.
.TP
\fB\-d\fP \fIfile\fP
true if
.I file
exists and is a directory.
.TP
\fB\-e\fP \fIfile\fP
true if
.I file
exists.
.TP
\fB\-f\fP \fIfile\fP
true if
.I file
exists and is an ordinary file.
.TP
\fB\-g\fP \fIfile\fP
true if
.I file
exists and has its setgid bit set.
.TP
\fB\-h\fP \fIfile\fP
true if
.I file
exists and is a symbolic link.
.TP
\fB\-k\fP \fIfile\fP
true if
.I file
exists and has its sticky bit set.
.TP
\fB\-n\fP \fIstring\fP
true if length of
.I string
is non-zero.
.TP
\fB\-o\fP \fIoption\fP
true if option named
.I option
is on.
.I option
may be a single character, in which case it is a single letter option name.
(See the
.B SPECIFYING OPTIONS
section of the
.IR zshoptions (1)
man page.)
.TP
\fB\-p\fP \fIfile\fP
true if
.I file
exists and is a fifo special file or a pipe.
.TP
\fB\-r\fP \fIfile\fP
true if
.I file
exists and is readable by current process.
.TP
\fB\-s\fP \fIfile\fP
true if
.I file
exists and has size greater than zero.
.TP
\fB\-t\fP \fIfd\fP
true if file descriptor number
.I fd
is open and associated with a terminal device.
(note: \fIfd\fP is not optional)
.TP
\fB\-u\fP \fIfile\fP
true if
.I file
exists and has its setuid bit set.
.TP
\fB\-w\fP \fIfile\fP
true if
.I file
exists and is writable by current process.
.TP
\fB\-x\fP \fIfile\fP
true if
.I file
exists and is executable by current process.
If
.I file
exists and is a directory, then the current process
has permission to search in the directory.
.TP
\fB\-z\fP \fIstring\fP
true if length of
.I string
is zero.
.TP
\fB\-L\fP \fIfile\fP
true if
.I file
exists and is a symbolic link.
.TP
\fB\-O\fP \fIfile\fP
true if
.I file
exists and is owned by the effective user id of this process.
.TP
\fB\-G\fP \fIfile\fP
true if
.I file
exists and its group matches the effective group id of this process.
.TP
\fB\-S\fP \fIfile\fP
true if
.I file
exists and is a socket.
.TP
\fB\-N\fP \fIfile\fP
true if
.I file
exists and its access time is not newer than its modification time.
.TP
\fIfile1\fP \fB\-nt\fP \fIfile2\fP
true if
.I file1
exists and is newer than
.IR file2 .
.TP
\fIfile1\fP \fB\-ot\fP \fIfile2\fP
true if
.I file1
exists and is older than
.IR file2 .
.TP
\fIfile1\fP \fB\-ef\fP \fIfile2\fP
true if
.I file1
and 
.I file2
exist and refer to the same file.
.TP
\fIstring\fP \fB==\fP \fIpattern\fP
.TP
\fIstring\fP \fB=\fP \fIpattern\fP
true if
.I string
matches
.IR pattern .
The first form is the preferred one.  The other form is for
backward compatibility and should be considered obsolete.
.TP
\fIstring\fP \fB!=\fP \fIpattern\fP
true if
.I string
does not match
.IR pattern .
.TP
\fIstring1\fP \fB<\fP \fIstring2\fP
true if
.I string1
comes before
.I string2
based on ASCII value of their characters.
.TP
\fIstring1\fP \fB>\fP \fIstring2\fP
true if
.I string1
comes after
.I string2
based on ASCII value of their characters.
.TP
\fIexp1\fP \fB\-eq\fP \fIexp2\fP
true if
.I exp1
is equal to
.IR exp2.
.TP
\fIexp1\fP \fB\-ne\fP \fIexp2\fP
true if
.I exp1
is not equal to
.IR exp2.
.TP
\fIexp1\fP \fB\-lt\fP \fIexp2\fP
true if
.I exp1
is less than
.IR exp2.
.TP
\fIexp1\fP \fB\-gt\fP \fIexp2\fP
true if
.I exp1
is greater than
.IR exp2.
.TP
\fIexp1\fP \fB\-le\fP \fIexp2\fP
true if
.I exp1
is less than or equal to
.IR exp2.
.TP
\fIexp1\fP \fB\-ge\fP \fIexp2\fP
true if
.I exp1
is greater than or equal to
.IR exp2.
.TP
\fB(\fP \fIexp\fP \fB)\fP
true if \fIexp\fP is true.
.TP
\fB!\fP \fIexp\fP
true if \fIexp\fP is false.
.TP
\fIexp1\fP \fB&&\fP \fIexp2\fP
true if \fIexp1\fP and \fIexp2\fP are both true.
.TP
\fIexp1\fP \fB|\||\fP \fIexp2\fP
true if either \fIexp1\fP or \fIexp2\fP is true.
.PD
.PP
In each of the above expressions, if
.I file
is of the form
\fB/dev/fd/\fP\fIn\fR,
where
.I n
is an integer,
then the test applied to the open file whose
descriptor number is
.IR n ,
even if the underlying system does not support
the \fB/dev/fd\fP directory.
.PD

.SH "COMPATIBILITY"
\fIZsh\fP tries to emulate \fIsh\fP or \fIksh\fP when it is invoked as
\fIsh\fP or \fIksh\fP respectively.  In this mode the following
parameters are not special and not initialized by the shell:
.BR ARGC ,
.BR argv ,
.BR cdpath ,
.BR fignore ,
.BR fpath ,
.BR HISTCHARS ,
.BR mailpath ,
.BR MANPATH ,
.BR manpath ,
.BR path ,
.BR prompt ,
.BR PROMPT ,
.BR PROMPT2 ,
.BR PROMPT3 ,
.BR PROMPT4 ,
.BR psvar ,
.BR status ,
.BR watch .
.PP
The usual \fIzsh\fP starup/shutdown scripts are not executed.  Login shells
source \fB/etc/profile\fP followed by \fB$HOME/.profile\fP.  If the
\fBENV\fP environment variable is set on invocation, \fB$ENV\fP is sourced
after the profile scripts.  The value of \fBENV\fP is subjected to
parameter expansion, command substitution, and arithmetic expansion before
being interpreted as a pathname.  Note that the \fBPRIVILEGED\fP option
also affects the execution of startup files.  See
\fIzshoptions\fP(%manext%) for more details.
.PP
The following options are set if the shell is invoked as \fIsh\fP or
\fIksh\fP:
.BR NO_BAD_PATTERN ,
.BR NO_BANG_HIST ,
.BR NO_BG_NICE ,
.BR NO_EQUALS ,
.BR NO_FUNCTION_ARGZERO ,
.BR GLOB_SUBST ,
.BR NO_HUP ,
.BR INTERACTIVE_COMMENTS ,
.BR KSH_ARRAYS ,
.BR NO_MULTIOS ,
.BR NO_NOMATCH ,
.BR RM_STAR_SILENT ,
.BR POSIX_BUILTINS ,
.BR SH_FILE_EXPANSION ,
.BR SH_GLOB ,
.BR SH_OPTION_LETTERS ,
.BR SH_WORD_SPLIT .
Additionally the
.B BSD_ECHO
and the
.B IGNORE_BRACES
options are set if \fIzsh\fP is invoked as \fIsh\fP and the
.BR KSH_OPTION_PRINT ,
.BR LOCAL_OPTIONS ,
.B PROMPT_SUBST
and
.B SINGLE_LINE_ZLE
options are set if \fIzsh\fP is invoked as \fIksh\fP.
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.