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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 26] 26.2 Don't Confuse Regular Expressions with Wildcards </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="1998-08-04T21:43:59Z"><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="ch26_01.htm"TITLE="26. Regular Expressions (Pattern Matching)"><LINKREL="prev"HREF="ch26_01.htm"TITLE="26.1 That's an Expression "><LINKREL="next"HREF="ch26_03.htm"TITLE="26.3 Understanding Expressions "></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="ch26_01.htm"TITLE="26.1 That's an Expression "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 26.1 That's an Expression "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 26<BR>Regular Expressions (Pattern Matching)</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch26_03.htm"TITLE="26.3 Understanding Expressions "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 26.3 Understanding Expressions "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-7948">26.2 Don't Confuse Regular Expressions with Wildcards </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-28307"></A><ACLASS="indexterm"NAME="AUTOID-28310"></A>Before we even start talking about regular expressions, a word ofcaution for beginners: regular expressions can be confusing because they look a lot like thefile matching patterns the shell uses.Both the shell and programs that use regular expressions have specialmeanings for the asterisk (<CODECLASS="literal">*</CODE>), question mark (<CODECLASS="literal">?</CODE>),parentheses (<CODECLASS="literal">()</CODE>), square brackets (<CODECLASS="literal">[]</CODE>),and vertical bar (<CODECLASS="literal">|</CODE>, the "pipe").</P><PCLASS="para">Some of these characters even act the same way - almost. </P><PCLASS="para">Just remember, the shells, <EMCLASS="emphasis">find</EM>,and<EMCLASS="emphasis">cpio</EM>use filename matching patterns and not regular expressions.</P><PCLASS="para">You also have to remember that shellmetacharacters are expanded before the shell passes the arguments tothe program. To prevent this expansion, the special characters in a regularexpression must be<SPANCLASS="link">quoted (<ACLASS="linkend"HREF="ch08_14.htm"TITLE="Bourne Shell Quoting ">8.14</A>)</SPAN>when passed as an argument from the shell.</P><PCLASS="para">The command:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>grep [A-Z]*.c chap[12]</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">could, for example, be interpreted by the shell as:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">grep Array.c Bug.c Comp.c chap1 chap2</PRE></BLOCKQUOTE></P><PCLASS="para">and so <EMCLASS="emphasis">grep</EM> would then try to find the pattern "Array.c" in files <EMCLASS="emphasis">Bug.c</EM>, <EMCLASS="emphasis">Comp.c</EM>, <EMCLASS="emphasis">chap1</EM>, and <EMCLASS="emphasis">chap2</EM>.</P><PCLASS="para">The simplest solution in most cases is to surround the regularexpression with single quotes (<CODECLASS="literal">'</CODE>).</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">BB</SPAN>, <SPANCLASS="authorinitials">DG, TOR</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="ch26_01.htm"TITLE="26.1 That's an Expression "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 26.1 That's an Expression "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="ch26_03.htm"TITLE="26.3 Understanding Expressions "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 26.3 Understanding Expressions "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">26.1 That's an Expression </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">26.3 Understanding Expressions </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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