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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 46] 46.6 Watch Out for Bourne Shell -e Bug </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="1998-08-04T21:55:40Z"><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="ch46_01.htm"TITLE="46. Shell Script Debugging and Gotchas"><LINKREL="prev"HREF="ch46_05.htm"TITLE="46.5 Stop Syntax Errors in String Tests "><LINKREL="next"HREF="ch46_07.htm"TITLE="46.7 Quoting and Command-Line Parameters "></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="ch46_05.htm"TITLE="46.5 Stop Syntax Errors in String Tests "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 46.5 Stop Syntax Errors in String Tests "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 46<BR>Shell Script Debugging and Gotchas</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch46_07.htm"TITLE="46.7 Quoting and Command-Line Parameters "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 46.7 Quoting and Command-Line Parameters "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-0234">46.6 Watch Out for Bourne Shell -e Bug </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55643"></A><ACLASS="indexterm"NAME="AUTOID-55646"></A>The Bourne shell <EMCLASS="emphasis">-e</EM> option should stop execution whena command returns a non-zero status.Does your <EMCLASS="emphasis">-e</EM> option seem to cause some <EMCLASS="emphasis">if</EM>commands to abort scripts?If so, you have a copy of the Buggy Bourne Shell, as distributed with4.2BSD, 4.3BSD, and probably several other systems. It can be identifiedby running:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>set -e</B></CODE><ACLASS="indexterm"NAME="AUTOID-55654"></A>$ <CODECLASS="userinput"><B>if false; then echo yipe; else echo ok; fi</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">and noting that the shell exits instead of printing <CODECLASS="literal">ok</CODE>, and by:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"> <ACLASS="co"HREF="ch44_09.htm"TITLE="44.9 Testing Your Success ">||</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">$ <CODECLASS="userinput"><B>set -e</B></CODE>$ <CODECLASS="userinput"><B>false || echo ok</B></CODE></PRE></TD></TR></TABLE></P><PCLASS="para">which also exits and should not, and by:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>set -e</B></CODE>$ <CODECLASS="userinput"><B>while false; do :; done</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55671"></A>To fix it, first get the source, and then change it in the obvious three places in<EMCLASS="emphasis">xec.c</EM>. You will have to learn Bournegol [the ALGOL-like dialect ofC that Steve Bourne used to write the original Bourne shell<EMCLASS="emphasis">-JP</EM> ].Another alternative is toreplace <EMCLASS="emphasis">/bin/sh</EM> with one of the<SPANCLASS="link">free <EMCLASS="emphasis">sh</EM> look-alikes (<ACLASS="linkend"HREF="ch01_08.htm"TITLE="There Are Many Shells ">1.8</A>)</SPAN>,provided you canfind one that is enough alike.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55679"></A><ACLASS="indexterm"NAME="AUTOID-55682"></A>As a workaround, you can <CODECLASS="literal">set +e</CODE> around all the tests that might fail.Unfortunately, some versions of the Buggy Bourne Shell do not even support<CODECLASS="literal">set +e</CODE>; here the only workaround is to run a<SPANCLASS="link">subshell (<ACLASS="linkend"HREF="ch38_04.htm"TITLE="Subshells ">38.4</A>)</SPAN>withoutthe <EMCLASS="emphasis">-e</EM> flag.</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">CT</SPAN> <SPANCLASS="bibliomisc">in <ACLASS="systemitem.newsgroup"HREF="news:comp.unix.questions">comp.unix.questions</A> on Usenet, 20 February 1990</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="ch46_05.htm"TITLE="46.5 Stop Syntax Errors in String Tests "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 46.5 Stop Syntax Errors in String Tests "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="ch46_07.htm"TITLE="46.7 Quoting and Command-Line Parameters "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 46.7 Quoting and Command-Line Parameters "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">46.5 Stop Syntax Errors in String Tests </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">46.7 Quoting and Command-Line Parameters </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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