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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 33] 33.8 Batch Editing Gotcha: Editors Bomb on Big Files </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="1998-08-04T21:46:54Z"><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="ch33_01.htm"TITLE="33. Batch Editing"><LINKREL="prev"HREF="ch33_07.htm"TITLE="33.7 ed/ex Batch Edits: Avoid Errors When No Match "><LINKREL="next"HREF="ch33_09.htm"TITLE="33.9 patch: Generalized Updating of Files that Differ "></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="ch33_07.htm"TITLE="33.7 ed/ex Batch Edits: Avoid Errors When No Match "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 33.7 ed/ex Batch Edits: Avoid Errors When No Match "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 33<BR>Batch Editing</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch33_09.htm"TITLE="33.9 patch: Generalized Updating of Files that Differ "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 33.9 patch: Generalized Updating of Files that Differ "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-7720">33.8 Batch Editing Gotcha: Editors Bomb on Big Files </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-36912"></A><ACLASS="indexterm"NAME="AUTOID-36915"></A><ACLASS="indexterm"NAME="AUTOID-36918"></A><ACLASS="indexterm"NAME="AUTOID-36921"></A>People use the <EMCLASS="emphasis">ed</EM> editor with script files to make global edits.But many versions of <EMCLASS="emphasis">ed</EM> can't edit large files. The <EMCLASS="emphasis">ex</EM>editor is usually better, but it has limits, too. How large is"large"? That depends on your version. Most <EMCLASS="emphasis">ed</EM>s I've seencan't handle more than about 100,000 characters.</P><PCLASS="para">There are no limits on<SPANCLASS="link"><EMCLASS="emphasis">sed</EM> (<ACLASS="linkend"HREF="ch34_24.htm"TITLE="Quick Reference: sed ">34.24</A>)</SPAN>,although you'll need to<SPANCLASS="link">save its output somehow (<ACLASS="linkend"HREF="ch34_03.htm"TITLE="Testing and Using a sed Script: checksed, runsed ">34.3</A>)</SPAN>,and your editing script mayhave to be changed to work with <EMCLASS="emphasis">sed</EM>.[1]Here's what you'll see when <EMCLASS="emphasis">ed</EM> bombs:</P><BLOCKQUOTECLASS="footnote"><PCLASS="para">[1] By default, <EMCLASS="emphasis">ed</EM> commands apply to the current line.<EMCLASS="emphasis">sed</EM> commands are global.Also, relative line addresses like <CODECLASS="literal">-5</CODE> don't work in <EMCLASS="emphasis">sed</EM>.</P></BLOCKQUOTE><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>cat edscr </B></CODE>s/Unix/UNIX/gw% <CODECLASS="userinput"><B>ed - words < edscr</B></CODE>?%</PRE></BLOCKQUOTE></P><PCLASS="para">The <CODECLASS="literal">?</CODE> is <EMCLASS="emphasis">ed</EM>'s verbose way of telling you thatsomething's wrong. This obscure message is especially bad if youwrite a shell script that edits multiple files in a loop; you may notnotice the error or be able to tell which file had the problem. Besure your script checks for errors!</P><PCLASS="para">Unfortunately for programmers, <EMCLASS="emphasis">ed</EM> may not return an error statusthat you can test.There are<SPANCLASS="link">workarounds (<ACLASS="linkend"HREF="ch46_09.htm"TITLE="If Command Doesn't Return a Status, Test the Error Messages">46.9</A>)</SPAN>,though. When the <CODECLASS="literal">ed -</CODE> command succeeds, it doesn't displayanything. The simplest way to find errors is to check for any outputon <EMCLASS="emphasis">stdout</EM> or <EMCLASS="emphasis">stderr</EM>. This chunk of a Bourne shell scriptshows how (your filename is in the<SPANCLASS="link">shell variable <CODECLASS="literal">$filename</CODE> (<ACLASS="linkend"HREF="ch06_08.htm"TITLE="Shell Variables ">6.8</A>)</SPAN>): </P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"><ACLASS="co"HREF="ch45_21.htm"TITLE="45.21 n>&m: Swap Standard Output and Standard Error ">2>&1</A> <ACLASS="co"HREF="ch44_20.htm"TITLE="44.20 test: Testing Files and Strings ">[ ]</A> <ACLASS="co"HREF="ch44_07.htm"TITLE="44.7 Exit Status of UNIX Processes ">$?</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">edout="`ed - $filename < edscr 2>&1`"if [ -n "$edout" -o $? -ne 0 ]then echo "$edout" 1>&2 echo "QUITTING: 'ed - $filename < edscr' bombed?!?" 1>&2 exit 1fi</PRE></TD></TR></TABLE></P><ACLASS="indexterm"NAME="AUTOID-36960"></A><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="ch33_07.htm"TITLE="33.7 ed/ex Batch Edits: Avoid Errors When No Match "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 33.7 ed/ex Batch Edits: Avoid Errors When No Match "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="ch33_09.htm"TITLE="33.9 patch: Generalized Updating of Files that Differ "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 33.9 patch: Generalized Updating of Files that Differ "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">33.7 ed/ex Batch Edits: Avoid Errors When No Match </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">33.9 patch: Generalized Updating of Files that Differ </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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