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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 9] 9.13 Multiline Commands, Secondary Prompts </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="1998-08-04T21:35:07Z"><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="ch09_01.htm"TITLE="9. Saving Time on the Command Line"><LINKREL="prev"HREF="ch09_12.htm"TITLE="9.12 The Bourne Shell for Loop "><LINKREL="next"HREF="ch09_14.htm"TITLE="9.14 Using Here Documents for Form Letters, etc. "></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="ch09_12.htm"TITLE="9.12 The Bourne Shell for Loop "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 9.12 The Bourne Shell for Loop "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 9<BR>Saving Time on the Command Line</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch09_14.htm"TITLE="9.14 Using Here Documents for Form Letters, etc. "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 9.14 Using Here Documents for Form Letters, etc. "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-1320">9.13 Multiline Commands, Secondary Prompts </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-10466"></A><ACLASS="indexterm"NAME="AUTOID-10469"></A><ACLASS="indexterm"NAME="AUTOID-10471"></A><ACLASS="indexterm"NAME="AUTOID-10474"></A><ACLASS="indexterm"NAME="AUTOID-10477"></A>Both the Bourne shell and the C shell support multiline commands.In the Bourne shell, a newline following an open quote (<CODECLASS="literal">'</CODE> or <CODECLASS="literal">"</CODE>),<ACLASS="indexterm"NAME="AUTOID-10482"></A>a pipe symbol (<CODECLASS="literal">|</CODE>), or a backslash (<CODECLASS="literal">\</CODE>) will not cause the commandto be executed.Instead, you'll get a secondary prompt (from the<EMCLASS="emphasis">PS2</EM> environment variable, set to <CODECLASS="literal">></CODE> by default) and you cancontinue the command on the next line.For example, to send a quick<SPANCLASS="link"><EMCLASS="emphasis">write</EM> (<ACLASS="linkend"HREF="ch01_33.htm"TITLE="UNIX Networking and Communications ">1.33</A>)</SPAN>message without making theother user wait for you to type the message:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>echo "We're leaving in 10 minutes. See you downstairs." |</B></CODE>> <CODECLASS="userinput"><B>write joanne</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">In the C shell, you can continue a line by<SPANCLASS="link">typing a backslash (<CODECLASS="literal">\</CODE>) before the newline (<ACLASS="linkend"HREF="ch08_15.htm"TITLE="Differences Between Bourne and C Shell Quoting ">8.15</A>)</SPAN>.You won't get the secondary prompt.</P><PCLASS="para">Obviously, this is a convenience if you're typing a longcommand line.It is a minor feature and one easilyoverlooked; however, it makes it much easier to usea program like<SPANCLASS="link"><EMCLASS="emphasis">sed</EM> (<ACLASS="linkend"HREF="ch34_24.htm"TITLE="Quick Reference: sed ">34.24</A>)</SPAN>from the command line.For example, if you know you chronically make thetypos "mvoe" (for "move") and "thier" (for"their"), you might be inspired to type the following command:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"> <ACLASS="co"HREF="ch43_13.htm"TITLE="43.13 The Text Formatters nroff, troff, ditroff, ... ">nroff</A> <ACLASS="co"HREF="ch43_02.htm"TITLE="43.2 Introduction to Printing on UNIX ">lp</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">$ <CODECLASS="userinput"><B>sed '</B></CODE>> <CODECLASS="userinput"><B>s/mvoe/move/g</B></CODE>> <CODECLASS="userinput"><B>s/thier/their/g' myfile | nroff -ms | lp</B></CODE></PRE></TD></TR></TABLE></P><PCLASS="para">More importantly, the ability to issue multilinecommands lets you use the shell's programmingfeatures interactively from the command line.In both the Bourne and the C shell, multiline programming constructsautomatically generate a secondary prompt (<CODECLASS="literal">></CODE> in the Bourneshell, <CODECLASS="literal">?</CODE> in the C shell) until the construct is completed.</P><PCLASS="para">For example, here's a place to use myfavorite programming construct for non-programmers, the<SPANCLASS="link"><EMCLASS="emphasis">for</EM> loop (<ACLASS="linkend"HREF="ch09_12.htm"TITLE="The Bourne Shell for Loop ">9.12</A>)</SPAN>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>for x in file1 file2 file3</B></CODE>> <CODECLASS="userinput"><B>do</B></CODE>> <CODECLASS="userinput"><B>sed 's/thier/their/g' $x > ,$x</B></CODE>> <CODECLASS="userinput"><B>mv ,$x $x</B></CODE>> <CODECLASS="userinput"><B>done</B></CODE>$</PRE></BLOCKQUOTE></P><PCLASS="para">Or in the C shell with<SPANCLASS="link"><EMCLASS="emphasis">foreach</EM> (<ACLASS="linkend"HREF="ch09_11.htm"TITLE="Repeating a Command with a foreach Loop ">9.11</A>)</SPAN>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>foreach x (file1 file2 file3)</B></CODE>? <CODECLASS="userinput"><B>sed 's/thier/their/g' $x > ,$x</B></CODE>? <CODECLASS="userinput"><B>mv ,$x $x</B></CODE>? <CODECLASS="userinput"><B>end</B></CODE>%</PRE></BLOCKQUOTE></P><PCLASS="para"> While a simple command like this could be savedinto a<SPANCLASS="link">shell script (<ACLASS="linkend"HREF="ch01_05.htm"TITLE="Anyone Can Program the Shell ">1.5</A>)</SPAN>,it is often even easier to use itinteractively.</P><PCLASS="para">Users of <EMCLASS="emphasis">sed</EM> should of course<SPANCLASS="link"> makesure their script works correctly before overwritingtheir original file . (<ACLASS="linkend"HREF="ch34_03.htm"TITLE="Testing and Using a sed Script: checksed, runsed ">34.3</A>)</SPAN></P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">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="ch09_12.htm"TITLE="9.12 The Bourne Shell for Loop "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 9.12 The Bourne Shell for Loop "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="ch09_14.htm"TITLE="9.14 Using Here Documents for Form Letters, etc. "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 9.14 Using Here Documents for Form Letters, etc. "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">9.12 The Bourne Shell for Loop </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">9.14 Using Here Documents for Form Letters, etc. </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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