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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 44] 44.20 test: Testing Files and Strings </TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly & Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1998-08-04T21:54:03Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-260-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch44_01.htm"TITLE="44. Shell Programming for the Uninitiated"><LINKREL="prev"HREF="ch44_19.htm"TITLE="44.19 The Bourne Shell set Command "><LINKREL="next"HREF="ch44_21.htm"TITLE="44.21 Picking a Name for a New Command "></HEAD><BODYBGCOLOR="#FFFFFF"TEXT="#000000"><DIVCLASS="htmlnav"><H1><IMGSRC="gifs/smbanner.gif"ALT="UNIX Power Tools"USEMAP="#srchmap"BORDER="0"></H1><MAPNAME="srchmap"><AREASHAPE="RECT"COORDS="0,0,466,58"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="467,0,514,18"HREF="jobjects/fsearch.htm"ALT="Search this book"></MAP><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch44_19.htm"TITLE="44.19 The Bourne Shell set Command "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 44.19 The Bourne Shell set Command "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 44<BR>Shell Programming for the Uninitiated</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch44_21.htm"TITLE="44.21 Picking a Name for a New Command "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 44.21 Picking a Name for a New Command "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-0020">44.20 test: Testing Files and Strings </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-51902"></A><ACLASS="indexterm"NAME="AUTOID-51904"></A><ACLASS="indexterm"NAME="AUTOID-51907"></A><ACLASS="indexterm"NAME="AUTOID-51910"></A><ACLASS="indexterm"NAME="AUTOID-51913"></A><ACLASS="indexterm"NAME="AUTOID-51916"></A><ACLASS="indexterm"NAME="AUTOID-51919"></A>UNIX has a command called <EMCLASS="emphasis">test</EM> that does a lot of usefultests. For instance, <EMCLASS="emphasis">test</EM> can check whether a file is writablebefore your script tries to write to it. It can treat the string in ashell variable as a number and do comparisons ("is that number lessthan 1000?"). You can combine tests, too ("if the file exists<EMCLASS="emphasis">and</EM> it's readable <EMCLASS="emphasis">and</EM> the message number is more than500..."). Some versions of <EMCLASS="emphasis">test</EM> have more tests than others.For a complete list, read your shell's manual page (if your shell has<EMCLASS="emphasis">test</EM><SPANCLASS="link">built in (<ACLASS="linkend"HREF="ch01_10.htm"TITLE="Internal and External Commands ">1.10</A>)</SPAN>)or the online <EMCLASS="emphasis">test</EM>(1) manual page.</P><PCLASS="para">The <EMCLASS="emphasis">test</EM> command returns a zero<SPANCLASS="link">status (<ACLASS="linkend"HREF="ch44_07.htm"TITLE="Exit Status of UNIX Processes ">44.7</A>)</SPAN>if the test was true or a non-zero status otherwise. So peopleusually use <EMCLASS="emphasis">test</EM> with <EMCLASS="emphasis">if</EM>, <EMCLASS="emphasis">while</EM>, or <EMCLASS="emphasis">until</EM>.Here's a way your program could check to see if the user has areadable file named <EMCLASS="emphasis">.signature</EM> in the home directory:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"><ACLASS="co"HREF="ch06_03.htm"TITLE="6.3 Predefined Environment Variables ">$HOME</A> <ACLASS="co"HREF="ch44_22.htm"TITLE="44.22 Finding a Program Name; Multiple Program Names ">$myname</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">if test -r <CODECLASS="literal">$HOME</CODE>/.signaturethen ...<EMCLASS="emphasis">Do whatever</EM>...else echo exit 1fi</PRE></TD></TR></TABLE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-51945"></A>The <EMCLASS="emphasis">test</EM> command also lets you test for something that<EMCLASS="emphasis">isn't</EM> true. Add an exclamation point (<CODECLASS="literal">!</CODE>) before thecondition you're testing. For example, the following test is true ifthe <EMCLASS="emphasis">.signature</EM> file is <EMCLASS="emphasis">not</EM> readable:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">if test ! -r $HOME/.signaturethen echo "$myname: Can't read your '.signature'. Quitting." 1>&2 exit 1fi</PRE></BLOCKQUOTE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-51956"></A><ACLASS="indexterm"NAME="AUTOID-51959"></A>UNIX also has a version of <EMCLASS="emphasis">test</EM> (a link to the sameprogram, actually) named <CODECLASS="replaceable"><I>[</I></CODE>. Yes, that's a left bracket. Youcan use it interchangeably with the <EMCLASS="emphasis">test</EM> command with oneexception: there has to be a matching right bracket (<CODECLASS="literal">]</CODE>) at theend of the test. The second example above could be rewritten thisway:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">if [ ! -r $HOME/.signature ]then echo "$myname: Can't read your '.signature'. Quitting." 1>&2 exit 1fi</PRE></BLOCKQUOTE></P><TABLECLASS="para.programreference"BORDER="1"><TR><THVALIGN="TOP"><ACLASS="programreference"HREF="examples/index.htm"TITLE="test">test</A><BR></TH><TDVALIGN="TOP">Be sure to leave space between the brackets and other text.There are a couple of other common gotchas caused by empty arguments; articles<ACLASS="xref"HREF="ch46_04.htm"TITLE="Stop Syntax Errors in Numeric Tests ">46.4</A>and<ACLASS="xref"HREF="ch46_05.htm"TITLE="Stop Syntax Errors in String Tests ">46.5</A>have workarounds.(For completeness, GNU <EMCLASS="emphasis">test</EM> is on the CD-ROM.But, for speed, we recommend using your shell's built-in version unlessyou need one of the GNU features.)</TD></TR></TABLE><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">JP</SPAN></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch44_19.htm"TITLE="44.19 The Bourne Shell set Command "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 44.19 The Bourne Shell set Command "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="book"HREF="index.htm"TITLE="UNIX Power Tools"><IMGSRC="gifs/txthome.gif"SRC="gifs/txthome.gif"ALT="UNIX Power Tools"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch44_21.htm"TITLE="44.21 Picking a Name for a New Command "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 44.21 Picking a Name for a New Command "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">44.19 The Bourne Shell set Command </TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="index"HREF="index/idx_0.htm"TITLE="Book Index"><IMGSRC="gifs/index.gif"SRC="gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172">44.21 Picking a Name for a New Command </TD></TR></TABLE><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><IMGSRC="gifs/smnavbar.gif"SRC="gifs/smnavbar.gif"USEMAP="#map"BORDER="0"ALT="The UNIX CD Bookshelf Navigation"><MAPNAME="map"><AREASHAPE="RECT"COORDS="0,0,73,21"HREF="../index.htm"ALT="The UNIX CD Bookshelf"><AREASHAPE="RECT"COORDS="74,0,163,21"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="164,0,257,21"HREF="../unixnut/index.htm"ALT="UNIX in a Nutshell"><AREASHAPE="RECT"COORDS="258,0,321,21"HREF="../vi/index.htm"ALT="Learning the vi Editor"><AREASHAPE="RECT"COORDS="322,0,378,21"HREF="../sedawk/index.htm"ALT="sed & awk"><AREASHAPE="RECT"COORDS="379,0,438,21"HREF="../ksh/index.htm"ALT="Learning the Korn Shell"><AREASHAPE="RECT"COORDS="439,0,514,21"HREF="../lrnunix/index.htm"ALT="Learning the UNIX Operating System"></MAP></DIV></BODY></HTML>⌨️ 快捷键说明
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