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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 2] 2.10 Gotchas in set prompt Test </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="1998-08-04T21:32:09Z"><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="ch02_01.htm"TITLE="2. Logging In"><LINKREL="prev"HREF="ch02_09.htm"TITLE="2.9 Speeding Up Your C Shell with set prompt Test "><LINKREL="next"HREF="ch02_11.htm"TITLE="2.11 Faster ksh and bash Startup with $- Test "></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="ch02_09.htm"TITLE="2.9 Speeding Up Your C Shell with set prompt Test "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 2.9 Speeding Up Your C Shell with set prompt Test "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 2<BR>Logging In</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch02_11.htm"TITLE="2.11 Faster ksh and bash Startup with $- Test "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 2.11 Faster ksh and bash Startup with $- Test "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-7783">2.10 Gotchas in set prompt Test </A></H2><PCLASS="para">Lots of users add an<SPANCLASS="link"><CODECLASS="literal">if</CODE> <CODECLASS="literal">(! $?prompt)</CODE> <CODECLASS="literal">exit</CODE> test (<ACLASS="linkend"HREF="ch02_09.htm"TITLE="Speeding Up Your C Shell with set prompt Test ">2.9</A>)</SPAN>to their <EMCLASS="emphasis">.cshrc</EM>files.It's gotten so common that some vendors add a workaround to defeat thetest.For instance, some versions of the<ACLASS="indexterm"NAME="AUTOID-3344"></A><ACLASS="indexterm"NAME="AUTOID-3347"></A><SPANCLASS="link"><EMCLASS="emphasis">which</EM> command (<ACLASS="linkend"HREF="ch50_08.htm"TITLE="Which Version Am I Using? ">50.8</A>)</SPAN>set the <EMCLASS="emphasis">prompt</EM> variable so that it can see your aliases "hidden"inside the <CODECLASS="literal">$?prompt</CODE> test. I've also seen a version of<EMCLASS="emphasis">at</EM> that starts an interactive shell to run jobs.</P><PCLASS="para">If you've buried commands after <CODECLASS="literal">if</CODE> <CODECLASS="literal"> (! $?prompt)</CODE> that should only be runon interactive shells or at login time, then you may have trouble.</P><PCLASS="para">There are workarounds.What you'll need depends on the problem you're trying to work around.</P><ULCLASS="itemizedlist"><LICLASS="listitem"><PCLASS="para">The version of <EMCLASS="emphasis">which</EM> on the CD-ROM works without reading your<EMCLASS="emphasis">.cshrc</EM> file, so there's no problem there.</P></LI><LICLASS="listitem"><PCLASS="para">Here's a way to stop the standard <EMCLASS="emphasis">which</EM> from reading parts ofyour <EMCLASS="emphasis">.cshrc</EM> that you don't want it to read.The first time you log in, this scheme sets a <EMCLASS="emphasis">CSHRC_READ</EM><ACLASS="indexterm"NAME="AUTOID-3369"></A><SPANCLASS="link">environment variable (<ACLASS="linkend"HREF="ch06_01.htm#UPT-ART-1170"TITLE="What Environment Variables Are Good For ">6.1</A>)</SPAN>.The variable will be copied into all<SPANCLASS="link">subshells (<ACLASS="linkend"HREF="ch38_04.htm"TITLE="Subshells ">38.4</A>)</SPAN>(like the one that <EMCLASS="emphasis">which</EM>starts).In subshells, the test <CODECLASS="literal">if</CODE> <CODECLASS="literal">($?CSHRC_READ)</CODE> will branch to the end of your<EMCLASS="emphasis">.cshrc</EM> file:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">if (! $?prompt) goto cshrc_end# COMMANDS BELOW HERE ARE READ ONLY BY INTERACTIVE SHELLS:alias foo bar ...if ($?CSHRC_READ) goto cshrc_end# COMMANDS BELOW HERE ARE READ ONLY AT LOGIN TIME:setenv CSHRC_READ yes ...cshrc_end:</PRE></BLOCKQUOTE></P><PCLASS="para"></P></LI><LICLASS="listitem"><PCLASS="para">If you have a buggy version of<SPANCLASS="link"><EMCLASS="emphasis">at</EM> (<ACLASS="linkend"HREF="ch40_03.htm"TITLE="The at Command ">40.3</A>)</SPAN>that runs jobs from interactiveshells, make<SPANCLASS="link">your own front-end to <EMCLASS="emphasis">at</EM> (<ACLASS="linkend"HREF="ch10_01.htm#UPT-ART-4930"TITLE="Creating Custom Commands ">10.1</A>)</SPAN><ACLASS="indexterm"NAME="AUTOID-3386"></A>that sets an environment variable named <EMCLASS="emphasis">AT</EM> temporarily before itsubmits the <EMCLASS="emphasis">at</EM> job.Add a test to your <EMCLASS="emphasis">.cshrc</EM> that quits if <EMCLASS="emphasis">AT</EM> is set:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"> <ACLASS="co"HREF="ch13_07.htm"TITLE="13.7 The () Subshell Operators ">( )</A> <ACLASS="co"HREF="ch10_06.htm"TITLE="10.6 Avoiding C Shell Alias Loops ">\at</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen"># at JOBS RUN INTERACTIVE SHELLS ON MY BUGGY VERSION OF UNIX.# WORKAROUND IS HERE AND IN THE at ALIAS BELOW:if ($?AT) goto cshrc_end ...alias at '(setenv AT yes; \at \!*)' ...cshrc_end:</PRE></TD></TR></TABLE></P><PCLASS="para">Most modern versions of <EMCLASS="emphasis">at</EM> save a copy of your environment andrestore it, later, when the <EMCLASS="emphasis">at</EM> job is run.At that time, the <EMCLASS="emphasis">AT</EM> environment variable will be set; the C shell willskip the parts of your <EMCLASS="emphasis">.cshrc</EM> that you want it to.It's ugly, but it works.</P></LI></UL><PCLASS="para">Those workarounds probably won't solve all the problems on your version ofUNIX, but I hope they'll give you some ideas.<ACLASS="indexterm"NAME="AUTOID-3402"></A><ACLASS="indexterm"NAME="AUTOID-3403"></A></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="ch02_09.htm"TITLE="2.9 Speeding Up Your C Shell with set prompt Test "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 2.9 Speeding Up Your C Shell with set prompt Test "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="ch02_11.htm"TITLE="2.11 Faster ksh and bash Startup with $- Test "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 2.11 Faster ksh and bash Startup with $- Test "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">2.9 Speeding Up Your C Shell with set prompt Test </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">2.11 Faster ksh and bash Startup with $- Test </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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