<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html40/loose.dtd">
<HTML>
<!-- Created on August, 9 2002 by texi2html 1.65 -->
<!--
Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author)
Karl Berry <karl@freefriends.org>
Olaf Bachmann <obachman@mathematik.uni-kl.de>
and many others.
Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>
Send bugs and suggestions to <texi2html@mathematik.uni-kl.de>
-->
<HEAD>
<TITLE>zsh: Conditional Expressions</TITLE>
<META NAME="description" CONTENT="zsh: Conditional Expressions">
<META NAME="keywords" CONTENT="zsh: Conditional Expressions">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<META NAME="Generator" CONTENT="texi2html 1.65">
</HEAD>
<BODY LANG="en" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#800080" ALINK="#FF0000">
<A NAME="SEC38"></A>
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_10.html#SEC37"> < </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_12.html#SEC39"> > </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_10.html#SEC37"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh.html#SEC_Top"> Up </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_12.html#SEC39"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_24.html#SEC195">Index</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H1> 11. Conditional Expressions </H1>
<!--docid::SEC38::-->
<A NAME="IDX128"></A>
<A NAME="IDX129"></A>
A <EM>conditional expression</EM> is used with the <TT>[[</TT>
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:
<P>
</P>
<DL COMPACT>
<DT><TT>-a</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists.
<P>
</P>
<DT><TT>-b</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is a block special file.
<P>
</P>
<DT><TT>-c</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is a character special file.
<P>
</P>
<DT><TT>-d</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is a directory.
<P>
</P>
<DT><TT>-e</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists.
<P>
</P>
<DT><TT>-f</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is a regular file.
<P>
</P>
<DT><TT>-g</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and has its setgid bit set.
<P>
</P>
<DT><TT>-h</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is a symbolic link.
<P>
</P>
<DT><TT>-k</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and has its sticky bit set.
<P>
</P>
<DT><TT>-n</TT> <VAR>string</VAR>
<DD>true if length of <VAR>string</VAR> is non-zero.
<P>
</P>
<DT><TT>-o</TT> <VAR>option</VAR>
<DD>true if option named <VAR>option</VAR> is on. <VAR>option</VAR>
may be a single character, in which case it is a single letter option name.
(See <A HREF="zsh_15.html#SEC75">15.1 Specifying Options</A>.)
<P>
</P>
<DT><TT>-p</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is a FIFO special file (named pipe).
<P>
</P>
<DT><TT>-r</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is readable by current process.
<P>
</P>
<DT><TT>-s</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and has size greater than zero.
<P>
</P>
<DT><TT>-t</TT> <VAR>fd</VAR>
<DD>true if file descriptor number <VAR>fd</VAR>
is open and associated with a terminal device.
(note: <VAR>fd</VAR> is not optional)
<P>
</P>
<DT><TT>-u</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and has its setuid bit set.
<P>
</P>
<DT><TT>-w</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is writable by current process.
<P>
</P>
<DT><TT>-x</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is executable by current process.
If <VAR>file</VAR> exists and is a directory, then the current process
has permission to search in the directory.
<P>
</P>
<DT><TT>-z</TT> <VAR>string</VAR>
<DD>true if length of <VAR>string</VAR> is zero.
<P>
</P>
<DT><TT>-L</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is a symbolic link.
<P>
</P>
<DT><TT>-O</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is owned by the effective user ID of this process.
<P>
</P>
<DT><TT>-G</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and its group matches
the effective group ID of this process.
<P>
</P>
<DT><TT>-S</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and is a socket.
<P>
</P>
<DT><TT>-N</TT> <VAR>file</VAR>
<DD>true if <VAR>file</VAR> exists and its access time is
not newer than its modification time.
<P>
</P>
<DT><VAR>file1</VAR> <TT>-nt</TT> <VAR>file2</VAR>
<DD>true if <VAR>file1</VAR> exists and is newer than <VAR>file2</VAR>.
<P>
</P>
<DT><VAR>file1</VAR> <TT>-ot</TT> <VAR>file2</VAR>
<DD>true if <VAR>file1</VAR> exists and is older than <VAR>file2</VAR>.
<P>
</P>
<DT><VAR>file1</VAR> <TT>-ef</TT> <VAR>file2</VAR>
<DD>true if <VAR>file1</VAR> and <VAR>file2</VAR> exist and refer to the same file.
<P>
</P>
<DT><VAR>string</VAR> <TT>=</TT> <VAR>pattern</VAR>
<DD><DT><VAR>string</VAR> <TT>==</TT> <VAR>pattern</VAR>
<DD>true if <VAR>string</VAR> matches <VAR>pattern</VAR>.
The `<TT>==</TT>' form is the preferred one. The `<TT>=</TT>' form is for
backward compatibility and should be considered obsolete.
<P>
</P>
<DT><VAR>string</VAR> <TT>!=</TT> <VAR>pattern</VAR>
<DD>true if <VAR>string</VAR> does not match <VAR>pattern</VAR>.
<P>
</P>
<DT><VAR>string1</VAR> <TT><</TT> <VAR>string2</VAR>
<DD>true if <VAR>string1</VAR> comes before <VAR>string2</VAR>
based on ASCII value of their characters.
<P>
</P>
<DT><VAR>string1</VAR> <TT>></TT> <VAR>string2</VAR>
<DD>true if <VAR>string1</VAR> comes after <VAR>string2</VAR>
based on ASCII value of their characters.
<P>
</P>
<DT><VAR>exp1</VAR> <TT>-eq</TT> <VAR>exp2</VAR>
<DD>true if <VAR>exp1</VAR> is numerically equal to <VAR>exp2</VAR>.
<P>
</P>
<DT><VAR>exp1</VAR> <TT>-ne</TT> <VAR>exp2</VAR>
<DD>true if <VAR>exp1</VAR> is numerically not equal to <VAR>exp2</VAR>.
<P>
</P>
<DT><VAR>exp1</VAR> <TT>-lt</TT> <VAR>exp2</VAR>
<DD>true if <VAR>exp1</VAR> is numerically less than <VAR>exp2</VAR>.
<P>
</P>
<DT><VAR>exp1</VAR> <TT>-gt</TT> <VAR>exp2</VAR>
<DD>true if <VAR>exp1</VAR> is numerically greater than <VAR>exp2</VAR>.
<P>
</P>
<DT><VAR>exp1</VAR> <TT>-le</TT> <VAR>exp2</VAR>
<DD>true if <VAR>exp1</VAR> is numerically less than or equal to <VAR>exp2</VAR>.
<P>
</P>
<DT><VAR>exp1</VAR> <TT>-ge</TT> <VAR>exp2</VAR>
<DD>true if <VAR>exp1</VAR> is numerically greater than or equal to <VAR>exp2</VAR>.
<P>
</P>
<DT><TT>(</TT> <VAR>exp</VAR> <TT>)</TT>
<DD>true if <VAR>exp</VAR> is true.
<P>
</P>
<DT><TT>!</TT> <VAR>exp</VAR>
<DD>true if <VAR>exp</VAR> is false.
<P>
</P>
<DT><VAR>exp1</VAR> <TT>&&</TT> <VAR>exp2</VAR>
<DD>true if <VAR>exp1</VAR> and <VAR>exp2</VAR> are both true.
<P>
</P>
<DT><VAR>exp1</VAR> <TT>||</TT> <VAR>exp2</VAR>
<DD>true if either <VAR>exp1</VAR> or <VAR>exp2</VAR> is true.
<P>
</DL>
<P>
Normal shell expansion is performed on the <VAR>file</VAR>, <VAR>string</VAR> and
<VAR>pattern</VAR> 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 <VAR>pattern</VAR> arguments; the patterns
are the same as those used for filename generation, see
<A HREF="zsh_13.html#SEC55">13.8 Filename Generation</A>, but there is no special behaviour
of `<TT>/</TT>' nor initial dots, and no glob qualifiers are allowed.
</P>
<P>
In each of the above expressions, if
<VAR>file</VAR> is of the form `<TT>/dev/fd/</TT><VAR>n</VAR>',
where <VAR>n</VAR> is an integer,
then the test applied to the open file whose
descriptor number is <VAR>n</VAR>,
even if the underlying system does not support
the <TT>/dev/fd</TT> directory.
</P>
<P>
In the forms which do numeric comparison, the expressions <VAR>exp</VAR>
undergo arithmetic expansion as if they were enclosed in <TT>$((...))</TT>.
</P>
<P>
For example, the following:
</P>
<P>
<TABLE><tr><td> </td><td class=example><pre>[[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.
</pre></td></tr></table><P>
tests if either file <TT>foo</TT> or file <TT>bar</TT> exists, and if so, if the
value of the parameter <TT>report</TT> begins with `<TT>y</TT>'; if the complete
condition is true, the message `<TT>File exists.</TT>' is printed.
<A NAME="Prompt Expansion"></A>
</P>
<P>
<HR SIZE="6">
<TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0>
<TR><TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_10.html#SEC37"> << </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_12.html#SEC39"> >> </A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT"> <TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh.html#SEC_Top">Top</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_toc.html#SEC_Contents">Contents</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_24.html#SEC195">Index</A>]</TD>
<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="zsh_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<BR>
<FONT SIZE="-1">
This document was generated
by <I>Peter Stephenson</I> on <I>August, 9 2002</I>
using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html
"><I>texi2html</I></A>
</FONT>
</BODY>
</HTML>
