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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 10] 10.7 How to Put if-then-else in a C Shell Alias </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="1998-08-04T21:35:54Z"><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="ch10_01.htm"TITLE="10. Aliases"><LINKREL="prev"HREF="ch10_06.htm"TITLE="10.6 Avoiding C Shell Alias Loops "><LINKREL="next"HREF="ch10_08.htm"TITLE="10.8 Fix Quoting in csh Aliases with makealias and quote "></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="ch10_06.htm"TITLE="10.6 Avoiding C Shell Alias Loops "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 10.6 Avoiding C Shell Alias Loops "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 10<BR>Aliases</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch10_08.htm"TITLE="10.8 Fix Quoting in csh Aliases with makealias and quote "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 10.8 Fix Quoting in csh Aliases with makealias and quote "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-5310">10.7 How to Put if-then-else in a C Shell Alias </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-12073"></A><ACLASS="indexterm"NAME="AUTOID-12076"></A><ACLASS="indexterm"NAME="AUTOID-12078"></A>The C shell's<SPANCLASS="link">brain damage (<ACLASS="linkend"HREF="ch47_02.htm"TITLE="C Shell Programming Considered Harmful ">47.2</A>)</SPAN>keeps you from using an<SPANCLASS="link"><EMCLASS="emphasis">if</EM> (<ACLASS="linkend"HREF="ch47_03.htm"TITLE="Conditional Statements with if ">47.3</A>)</SPAN>with an <EMCLASS="emphasis">else</EM> in an alias.You have to use a<SPANCLASS="link">sourceable script (<ACLASS="linkend"HREF="ch10_05.htm"TITLE="Sourceable Scripts ">10.5</A>)</SPAN>.Or that's what I thought until I saw an article by Lloyd Zusman on<EMCLASS="emphasis">comp.unix.questions</EM> in December 1987.He'd saved an earlier posting on that group (but without its author's name)that showed how.The trick: use enough backslashes (<CODECLASS="literal">\</CODE>) and the<SPANCLASS="link"><EMCLASS="emphasis">eval</EM> (<ACLASS="linkend"HREF="ch08_10.htm"TITLE="eval: When You Need Another Chance ">8.10</A>)</SPAN><ACLASS="indexterm"NAME="AUTOID-12090"></A>command.</P><PCLASS="para">As an example, here's an alias named <EMCLASS="emphasis">C</EM> for<SPANCLASS="link">compiling (<ACLASS="linkend"HREF="ch52_08.htm"TITLE="Building Programs from Source Code ">52.8</A>)</SPAN>C programs.It needs the <EMCLASS="emphasis">executable</EM> filename (like <CODECLASS="literal">C prog</CODE>), not the source filename (like <CODECLASS="literal">C prog.c</CODE>).If you type a filename ending in <EMCLASS="emphasis">.c</EM>, it complains and quits.Else, it:</P><ULCLASS="itemizedlist"><LICLASS="listitem"><PCLASS="para">Renames any old <EMCLASS="emphasis">prog</EM> file to <EMCLASS="emphasis">prog.old</EM>,</P></LI><LICLASS="listitem"><PCLASS="para">Prints the message <CODECLASS="replaceable"><I>prog</I></CODE><CODECLASS="literal"> SENT TO cc</CODE>,</P></LI><LICLASS="listitem"><PCLASS="para">Compiles <EMCLASS="emphasis">prog.c</EM>,</P></LI><LICLASS="listitem"><PCLASS="para">And - if there's a <EMCLASS="emphasis">prog</EM> file (if the compilesucceeded)-runs <EMCLASS="emphasis">chmod 311 prog</EM> to protect the file fromaccidental reading with a command like <EMCLASS="emphasis">cat *</EM> or <EMCLASS="emphasis">more *</EM>.</P></LI></UL><PCLASS="para">Your alias doesn't need to be as complicated.But this one shows some tricks, like putting an <EMCLASS="emphasis">if</EM> inside the<EMCLASS="emphasis">if</EM>, that you might want to use.The expressions like <CODECLASS="literal">=~</CODE> and <CODECLASS="literal">-e</CODE> are explained in article<ACLASS="xref"HREF="ch47_04.htm"TITLE="C Shell Variable Operators and Expressions ">47.4</A>.<ACLASS="indexterm"NAME="AUTOID-12124"></A>Watch your quoting - remember that the shell strips off one level ofquoting<SPANCLASS="link">when you set the alias (<ACLASS="linkend"HREF="ch10_03.htm"TITLE="C Shell Aliases with Command-Line Arguments ">10.3</A>)</SPAN>and another during the first pass ofthe <EMCLASS="emphasis">eval</EM>.Follow this example and you'll probably be fine:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen"> # COMPILE AND chmod C PROGRAMS; DON'T USE .c ON END OF FILENAME.alias C 'eval "if (\!* =~ *.c) then \\ echo "C quitting: no .c on end of \!* please." \\else \\ if (-e \!*) mv \!* \!*.old \\ echo \!*.c SENT TO cc \\ cc -s \!*.c -o \!* \\ if (-e \!*) chmod 311 \!* \\endif"'</PRE></BLOCKQUOTE></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="ch10_06.htm"TITLE="10.6 Avoiding C Shell Alias Loops "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 10.6 Avoiding C Shell Alias Loops "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="ch10_08.htm"TITLE="10.8 Fix Quoting in csh Aliases with makealias and quote "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 10.8 Fix Quoting in csh Aliases with makealias and quote "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">10.6 Avoiding C Shell Alias Loops </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">10.8 Fix Quoting in csh Aliases with makealias and quote </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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