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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 45] 45.16 Standard Input to a for Loop </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="1998-08-04T21:54:39Z"><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="ch45_01.htm"TITLE="45. Shell Programming for the Initiated"><LINKREL="prev"HREF="ch45_15.htm"TITLE="45.15 How to Unset all Command-Line Parameters "><LINKREL="next"HREF="ch45_17.htm"TITLE="45.17 Making a for Loop with Multiple Variables "></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="ch45_15.htm"TITLE="45.15 How to Unset all Command-Line Parameters "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 45.15 How to Unset all Command-Line Parameters "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 45<BR>Shell Programming for the Initiated</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch45_17.htm"TITLE="45.17 Making a for Loop with Multiple Variables "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 45.17 Making a for Loop with Multiple Variables "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-5370">45.16 Standard Input to a for Loop </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-53305"></A><ACLASS="indexterm"NAME="AUTOID-53308"></A><ACLASS="indexterm"NAME="AUTOID-53311"></A>An obvious place to use a Bourne shell<SPANCLASS="link"><EMCLASS="emphasis">for</EM> loop (<ACLASS="linkend"HREF="ch44_16.htm"TITLE="Handling Command-Line Arguments with a for Loop ">44.16</A>)</SPAN>is to step through alist of arguments - from the command line or a variable.But combine the loop with<SPANCLASS="link">backquotes (<ACLASS="linkend"HREF="ch09_16.htm"TITLE="Command Substitution ">9.16</A>)</SPAN>and<SPANCLASS="link"><EMCLASS="emphasis">cat</EM> (<ACLASS="linkend"HREF="ch25_02.htm"TITLE="Four Ways to Skin a cat ">25.2</A>)</SPAN>,and the loop will step through the words on standard input.</P><PCLASS="para">Here's an example:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">for x in `cat`do <ICLASS="lineannotation">...handle $x</I>done</PRE></BLOCKQUOTE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-53324"></A><ACLASS="indexterm"NAME="AUTOID-53327"></A><ACLASS="indexterm"NAME="AUTOID-53330"></A><ACLASS="indexterm"NAME="AUTOID-53333"></A>Because this method splits the input into separate words, no matter how manywords are on each input line, it can be more convenient than a<EMCLASS="emphasis">while</EM> loop running the <EMCLASS="emphasis">read</EM> command, as in article<ACLASS="xref"HREF="ch09_20.htm"TITLE="Too Many Files for the Command Line ">9.20</A>.When you use this script interactively though, the loop won't startrunning untilyou've typed all of the input; using <EMCLASS="emphasis">while read</EM> will run the loop aftereach line of input.</P><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="ch45_15.htm"TITLE="45.15 How to Unset all Command-Line Parameters "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 45.15 How to Unset all Command-Line Parameters "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="ch45_17.htm"TITLE="45.17 Making a for Loop with Multiple Variables "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 45.17 Making a for Loop with Multiple Variables "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">45.15 How to Unset all Command-Line Parameters </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">45.17 Making a for Loop with Multiple Variables </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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