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<HTML><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><!-- Created on September, 12  2004 by texi2html 1.64 --><!-- 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>Autoconf, Automake, and Libtool: Test</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: Test"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: Test"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><META NAME="Generator" CONTENT="texi2html 1.64"><script language="Javascript"><!--    // Check the browser version.    function checkVersion() {      if (navigator.appVersion.charAt(0)>=3) return true;      if (navigator.appVersion.charAt(0)>=4) return true;      else return false; 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<TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_217.html#SEC217" onMouseover="img_act('back')" onMouseout="img_inact('back')"><IMG SRC="back.png" BORDER="0" ALT="FastBack: Variables" ALIGN="MIDDLE" NAME="back"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_210.html#SEC210" onMouseover="img_act('up')" onMouseout="img_inact('up')"><IMG SRC="up.png" BORDER="0" ALT="Up: Sh Implementation" ALIGN="MIDDLE" NAME="up"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_219.html#SEC219" onMouseover="img_act('forward')" onMouseout="img_inact('forward')"><IMG SRC="forward.png" BORDER="0" ALT="FastForward: Environment" ALIGN="MIDDLE" NAME="forward"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook.html#SEC_Top" onMouseover="img_act('home')" onMouseout="img_inact('home')"><IMG SRC="home.png" BORDER="0" ALT="Top: Autoconf, Automake, and Libtool" ALIGN="MIDDLE" NAME="home"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_toc.html#SEC_Contents" onMouseover="img_act('toc')" onMouseout="img_inact('toc')"><IMG SRC="toc.png" BORDER="0" ALT="Contents: Table of Contents" ALIGN="MIDDLE" NAME="toc"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_285.html#SEC285" onMouseover="img_act('index')" onMouseout="img_inact('index')"><IMG SRC="index.png" BORDER="0" ALT="Index: Index" ALIGN="MIDDLE" NAME="index"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_abt.html#SEC_About" onMouseover="img_act('help')" onMouseout="img_inact('help')"><IMG SRC="help.png" BORDER="0" ALT="About: About this document" ALIGN="MIDDLE" NAME="help"></A></TD></TR></TABLE></TD><TD ALIGN="LEFT"><H3> 22.2.6 [ </H3><!--docid::SEC216::--><P>Although technically equivalent, <CODE>test</CODE> is preferable to<CODE>[</CODE> in shell code written in conjunction with Autoconf, since<SAMP>`['</SAMP> is also used for M4 quoting in Autoconf.  Your code will bemuch easier to read (and write) if you abstain from the use of <SAMP>`['</SAMP>.</P><P>Except in the most degenerate shells, <CODE>test</CODE> is a shell builtinto save the overhead of starting another process, and is no slower than<SAMP>`['</SAMP>.  It does mean, however, that there is a huge range of featureswhich are not implemented often enough that you can use them freelywithin a truly portable script.   The less obvious ones to avoid are<SAMP>`-a'</SAMP> and <SAMP>`-o'</SAMP> -- the logical `and' and `or'operations.  A good litmus test for the portability of any shell featureis to see whether that feature is used in the source of Autoconf, and itturns out that <SAMP>`-a'</SAMP> and <SAMP>`-o'</SAMP> <EM>are</EM> used here andthere, but never more than once in a single command.  All the same, toavoid any confusion, I always avoid them entirely.  I would not use thefollowing, for example:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>test foo -a bar</pre></td></tr></table></P><P>Instead I would run test twice, like this:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>test foo &#38;&#38; test bar</pre></td></tr></table></P><P>The negation operator of <CODE>test</CODE> is quite portable and can beused in portable shell scripts.  For example:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>if test ! foo; then bar; fi</pre></td></tr></table></P><P>The negation operator of <CODE>if</CODE> is not at all portable and shouldbe avoided.  The following would generate a syntax error on some shellimplementations:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>if ! test foo; then bar; fi</pre></td></tr></table></P><P>An implication of this axiom is that when you need to branch if acommand fails, and that command is not <CODE>test</CODE>, you cannot usethe negation operator.  The easiest way to work around this is to usethe <SAMP>`else'</SAMP> clause of the un-negated <CODE>if</CODE>, like this:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>if foo; then :; else bar; fi</pre></td></tr></table></P><P>Notice the use of the <CODE>:</CODE> builtin as a null operation when<CODE>foo</CODE> doesn't fail.</P><P>The <CODE>test</CODE> command does not cope with missing or additionalarguments, so you must take care to ensure that the shell does notremove arguments or introduce new ones during variable and quoteexpansions.  The best way to do that is to enclose any variables indouble quotes.  You should also add a single character prefix to bothsides in case the value of the expansion is a valid option to<CODE>test</CODE>:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>$ for foo in "" "!" "bar" "baz quux"; do&#62;   test x"$foo" = x"bar" &#38;&#38; echo 1 || echo 0&#62; done0010</pre></td></tr></table></P><P>Here, you can see that using the <SAMP>`x'</SAMP> prefix for the first operandsaves <CODE>test</CODE> from interpreting the <SAMP>`!'</SAMP> argument as a realoption, or from choking on an empty string -- something you must alwaysbe aware of, or else the following behaviour will ensue:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>$ foo=!$ test "$foo" = "bar" &#38;&#38; echo 1 || echo 0test: argument expected0$ foo=""$ test "$foo" = "bar" &#38;&#38; echo 1 || echo 0test: argument expected0</pre></td></tr></table></P><P>Also, the double quote marks help <CODE>test</CODE> cope with strings thatcontain whitespace.  Without the double quotes, you will see this errors:</P><P><TABLE width=100%><tr><td>&nbsp;</td><td class=example bgcolor=#6688aa><br><pre>$ foo="baz quux"$ test x$foo = "bar" &#38;&#38; echo 1 || echo 0test: too many arguments0</pre></td></tr></table></P><P>You shouldn't rely on the default behaviour of test (to return `true'if its single argument has non-zero length), use the <SAMP>`-n'</SAMP> optionto force that behaviour if it is what you want.  Beyond that, the otherthing you need to know about <CODE>test</CODE>, is that if you use operatorsother than those below, you are reducing the portability of your code:</P><P><DL COMPACT><DT><SAMP>`-n'</SAMP> <VAR>string</VAR><DD><VAR>string</VAR> is non-empty.<DT><SAMP>`-z'</SAMP> <VAR>string</VAR><DD><VAR>string</VAR> is empty.<DT><VAR>string1</VAR> = <VAR>string2</VAR><DD>Both strings are identical.<DT><VAR>string1</VAR> != <VAR>string2</VAR><DD>The strings are not the same.<DT><SAMP>`-d'</SAMP> <VAR>file</VAR><DD><VAR>file</VAR> exists and is a directory.<DT><SAMP>`-f'</SAMP> <VAR>file</VAR><DD><VAR>file</VAR> exists and is a regular file.</DL><P>You can also use the following, provided that you don't mix them withina single invocation of <CODE>test</CODE>:</P><P><DL COMPACT><DT><VAR>expression</VAR> <SAMP>`-a'</SAMP> <VAR>expression</VAR><DD>Both expressions evaluate to `true'.<DT><VAR>expression</VAR> <SAMP>`-o'</SAMP> <VAR>expression</VAR><DD>Neither expression evaluates to `false'.</DL><P><A NAME="Variables"></A></TR></TABLE><BR>  <FONT SIZE="-1">This document was generatedby <I>Gary V. Vaughan</I> on <I>September, 12  2004</I>using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html"><I>texi2html</I></A></BODY></HTML>
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