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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 2] 2.9 Speeding Up Your C Shell with 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="1998-08-04T21:32:07Z"><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="ch02_01.htm"TITLE="2. Logging In"><LINKREL="prev"HREF="ch02_08.htm"TITLE="2.8 Identifying Login Shells "><LINKREL="next"HREF="ch02_10.htm"TITLE="2.10 Gotchas in set prompt 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_08.htm"TITLE="2.8 Identifying Login Shells "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 2.8 Identifying Login Shells "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_10.htm"TITLE="2.10 Gotchas in set prompt Test "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 2.10 Gotchas in set prompt Test "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-5320">2.9 Speeding Up Your C Shell with set prompt Test </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-3279"></A><ACLASS="indexterm"NAME="AUTOID-3282"></A><ACLASS="indexterm"NAME="AUTOID-3285"></A><ACLASS="indexterm"NAME="UPT-ART-5320-IX-SET-PROMPT-TEST"></A><ACLASS="indexterm"NAME="UPT-ART-5320-IX-IF-PROMPT-TEST"></A>Every time you start a C shell - in a<SPANCLASS="link">shell escape (<ACLASS="linkend"HREF="ch30_26.htm"TITLE="Shell Escapes: Running One UNIX Command While Using Another">30.26</A>)</SPAN>,the<SPANCLASS="link"><EMCLASS="emphasis">su</EM> (<ACLASS="linkend"HREF="ch22_22.htm"TITLE="The su Command Isn't Just for the Superuser ">22.22</A>)</SPAN>command, a shell script, an<SPANCLASS="link"><EMCLASS="emphasis">at</EM> job (<ACLASS="linkend"HREF="ch40_01.htm#UPT-ART-2313"TITLE="Off-Peak Job Submission ">40.1</A>)</SPAN>,etc.-the <EMCLASS="emphasis">csh</EM> readsthe <EMCLASS="emphasis">.cshrc</EM> file in your home directory.Some of those shells are "noninteractive," which meansthe shell is running a single command or reading from a<SPANCLASS="link">script file (<ACLASS="linkend"HREF="ch01_05.htm"TITLE="Anyone Can Program the Shell ">1.5</A>)</SPAN>-you won't be typing any commands yourself.If your <EMCLASS="emphasis">.cshrc</EM> has commands like<SPANCLASS="link"><EMCLASS="emphasis">alias</EM> (<ACLASS="linkend"HREF="ch10_02.htm"TITLE="Aliases for Common Commands ">10.2</A>)</SPAN>,<SPANCLASS="link"><EMCLASS="emphasis">set cdpath</EM> (<ACLASS="linkend"HREF="ch14_05.htm"TITLE="Saving Time When You Change Directories: cdpath ">14.5</A>)</SPAN>,and others that are only useful in interactive shells, it wastes timeto make noninteractive shells read them.</P><PCLASS="para">You can tell the shell to skip commands that will only be used ininteractive shells.Set up your <EMCLASS="emphasis">.cshrc</EM> this way:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"> <ACLASS="co"HREF="ch47_03.htm"TITLE="47.3 Conditional Statements with if ">if</A> <ACLASS="co"HREF="ch47_04.htm"TITLE="47.4 C Shell Variable Operators and Expressions ">! $?</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen"># COMMANDS FOR ALL C SHELLS:set path = (...<EMCLASS="emphasis">whatever</EM>...) ...if (! $?prompt) goto cshrc_end# COMMANDS FOR INTERACTIVE SHELLS ONLY:alias foo bar ...set cdpath = (~ ~joe/project)cshrc_end:</PRE></TD></TR></TABLE></P><TABLECLASS="para.programreference"BORDER="1"><TR><THVALIGN="TOP"><ACLASS="xref.warning"HREF="ch02_10.htm"TITLE="2.10 Gotchas in set prompt Test ">Warning!</A> </TH><TDVALIGN="TOP"> The <CODECLASS="literal">! $?prompt</CODE> succeeds only on noninteractive shells, when theshell hasn't set the <EMCLASS="emphasis">prompt</EM> variable.On noninteractive shells, the command <CODECLASS="literal">goto cshrc_end</CODE> makes theshell skip to the line at the end of the file labeled <CODECLASS="literal">cshrc_end:</CODE>.</TD></TR></TABLE><PCLASS="para">Of course, if you<SPANCLASS="link">set your own prompt (<ACLASS="linkend"HREF="ch07_01.htm#UPT-ART-4820"TITLE="Why Change Your Prompt? ">7.1</A>)</SPAN>,be sure to do it on some line below the <CODECLASS="literal">! $?prompt</CODE> test.Otherwise, the test will always fail!</P><BLOCKQUOTECLASS="note"><PCLASS="para"><STRONG>NOTE:</STRONG> Some books tell you to use a test like this instead:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">if (! $?prompt) exit# commands for interactive shells only: ...</PRE></BLOCKQUOTE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-3325"></A>But some C shells will log out when they see the <EMCLASS="emphasis">exit</EM> commandin a <EMCLASS="emphasis">.cshrc</EM> file.Using <CODECLASS="literal">goto cshrc_end</CODE> is more portable.</P></BLOCKQUOTE><PCLASS="para">Article<ACLASS="xref"HREF="ch07_03.htm"TITLE="C Shell Prompt Causes Problems in vi, rsh, etc. ">7.3</A>explains another problem that this <CODECLASS="literal">$?prompt</CODE> test solves.</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_08.htm"TITLE="2.8 Identifying Login Shells "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 2.8 Identifying Login Shells "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_10.htm"TITLE="2.10 Gotchas in set prompt Test "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 2.10 Gotchas in set prompt Test "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">2.8 Identifying Login Shells </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">2.10 Gotchas in set prompt 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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