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<HTML><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><!-- Created on September, 12 2004 by texi2html 1.64 --><!-- Written by: Lionel Cons <Lionel.Cons@cern.ch> (original author) Karl Berry <karl@freefriends.org> Olaf Bachmann <obachman@mathematik.uni-kl.de> and many others.Maintained by: Olaf Bachmann <obachman@mathematik.uni-kl.de>Send bugs and suggestions to <texi2html@mathematik.uni-kl.de> --><HEAD><TITLE>Autoconf, Automake, and Libtool: Utilities</TITLE><META NAME="description" CONTENT="Autoconf, Automake, and Libtool: Utilities"><META NAME="keywords" CONTENT="Autoconf, Automake, and Libtool: Utilities"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><META NAME="Generator" CONTENT="texi2html 1.64"><script language="Javascript"><!-- // Check the browser version. function checkVersion() { if (navigator.appVersion.charAt(0)>=3) return true; if (navigator.appVersion.charAt(0)>=4) return true; else return false; } if (checkVersion()) { homeon = new Image(); 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document [imgName].src = imgOff; } }// --></SCRIPT></HEAD><BODY LANG="EN" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#6688AA" VLINK="#336688" ALINK="#808080"><A NAME="SEC220"></A><TABLE BORDER=0 CELLPADDING=0 CELLSPACING=10><TR VALIGN="TOP"><TD ALIGN="MIDDLE" WIDTH=50 BGCOLOR="#e6e6e6"><TABLE CELLPADDING=1 CELLSPACING=1 BORDER=0><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_219.html#SEC219" onMouseover="img_act('prev')" onMouseout="img_inact('prev')"><IMG SRC="prev.png" BORDER="0" ALT="Back: Environment" ALIGN="MIDDLE" NAME="prev"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_221.html#SEC221" onMouseover="img_act('next')" onMouseout="img_inact('next')"><IMG SRC="next.png" BORDER="0" ALT="Forward: Writing New Macros for Autoconf" ALIGN="MIDDLE" NAME="next"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"> <TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_208.html#SEC208" onMouseover="img_act('back')" onMouseout="img_inact('back')"><IMG SRC="back.png" BORDER="0" ALT="FastBack: Writing Portable Bourne Shell" ALIGN="MIDDLE" NAME="back"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_208.html#SEC208" onMouseover="img_act('up')" onMouseout="img_inact('up')"><IMG SRC="up.png" BORDER="0" ALT="Up: Writing Portable Bourne Shell" ALIGN="MIDDLE" NAME="up"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_221.html#SEC221" onMouseover="img_act('forward')" onMouseout="img_inact('forward')"><IMG SRC="forward.png" BORDER="0" ALT="FastForward: Writing New Macros for Autoconf" ALIGN="MIDDLE" NAME="forward"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook.html#SEC_Top" onMouseover="img_act('home')" onMouseout="img_inact('home')"><IMG SRC="home.png" BORDER="0" ALT="Top: Autoconf, Automake, and Libtool" ALIGN="MIDDLE" NAME="home"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_toc.html#SEC_Contents" onMouseover="img_act('toc')" onMouseout="img_inact('toc')"><IMG SRC="toc.png" BORDER="0" ALT="Contents: Table of Contents" ALIGN="MIDDLE" NAME="toc"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_285.html#SEC285" onMouseover="img_act('index')" onMouseout="img_inact('index')"><IMG SRC="index.png" BORDER="0" ALT="Index: Index" ALIGN="MIDDLE" NAME="index"></A></TD></TR><TR VALIGN="TOP" ALIGN="LEFT"><TD VALIGN="MIDDLE" ALIGN="LEFT"><A HREF="autobook_abt.html#SEC_About" onMouseover="img_act('help')" onMouseout="img_inact('help')"><IMG SRC="help.png" BORDER="0" ALT="About: About this document" ALIGN="MIDDLE" NAME="help"></A></TD></TR></TABLE></TD><TD ALIGN="LEFT"><H2> 22.4 Utilities </H2><!--docid::SEC220::--><P>The utility programs commonly executed by shell scripts can have a hugeimpact on the portability of shell scripts, and it is important to knowwhich utilities are universally available, and any differences certainimplementations of these utilities may exhibit. According to theGNU standards document, you can rely on having access to theseutilities from your scripts:</P><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>cat cmp cp diff echo egrep expr false grep install-infoln ls mkdir mv pwd rm rmdir sed sleep sort tar test touch true</pre></td></tr></table></P><P>Here are some things that you must be aware of when using some of thetools listed above:</P><P><DL COMPACT><DT><CODE>cat</CODE><DD>Host architectures supply <CODE>cat</CODE> implementations withconflicting interpretations of, or entirely missing, the various commandline options. You should avoid using any command line options to thiscommand.<P><DT><CODE>cp</CODE> and <CODE>mv</CODE><DD>Unconditionally duplicated or otherwise open file descriptors can not bedeleted on many operating systems, and worse on Windows the destinationfiles cannot even be moved. Constructs like this must be avoided, forexample.<P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>exec > foomv foo bar</pre></td></tr></table></P><P><DT><CODE>echo</CODE><DD>The <CODE>echo</CODE> command has at least two flavors: the one takes a<SAMP>`-n'</SAMP> option to suppress the automatic newline at the end of theechoed string; the other uses an embedded <SAMP>`\c'</SAMP> notation as the lastcharacter in the echoed string for the same purpose.<P>If you need to emit a string without a trailing newline character, youcan use the following script fragment to discover which flavor of<CODE>echo</CODE> you are using:</P><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>case echo "testing\c"`,`echo -n testing` in *c*,-n*) echo_n= echo_c='<A NAME="DOCF53" HREF="autobook_fot.html#FOOT53">(53)</A>' ;; *c*,*) echo_n=-n echo_c= ;; *) echo_n= echo_c='\c ;;esac</pre></td></tr></table></P><P>Any <CODE>echo</CODE> command after the shell fragment above, whichshouldn't move the cursor to a new line, can now be written like so:</P><P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>echo $echo_n "prompt:$echo_c"</pre></td></tr></table></P><P>In addition, you should try to avoid backslashes in <CODE>echo</CODE>arguments unless they are expanded by the shell. Some implementationsinterpret them and effectively perform another backslash expansion pass,where equally many implementations do not. This can become a reallyhairy problem if you need to have an <CODE>echo</CODE> command whichdoesn't perform backslash expansion, and in fact the first 150 lines ofthe <CODE>ltconfig</CODE> script distributed with Libtool are devoted tofinding such a command.</P><P><DT><CODE>ln</CODE><DD>Not all systems support soft links. You should use the Autoconf macro<SAMP>`AC_PROG_LN_S'</SAMP> to discover what the target architecture supports,and assign the result of that test to a variable. Whenever yousubsequently need to create a link you can use the command stored in thevariable to do so.<P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>LN_S=@LN_S@...$LN_S $top_srcdir/foo $dist_dir/foo</pre></td></tr></table></P><P>Also, you cannot rely on support for the <SAMP>`-f'</SAMP> option from allimplementations of <CODE>ln</CODE>. Use <CODE>rm</CODE> before calling<CODE>ln</CODE> instead.</P><P><DT><CODE>mkdir</CODE><DD>Unfortunately, <SAMP>`mkdir -p'</SAMP> is not as portable as we might like. Youmust either create each directory in the path in turn, or use the<CODE>mkinstalldirs</CODE> script supplied by Automake.<P><DT><CODE>sed</CODE><DD>When you resort to using <CODE>sed</CODE> (rather, use <CODE>case</CODE> or<CODE>expr</CODE> if you can), there is no need to introduce command linescripts using the <SAMP>`-e'</SAMP> option. Even when you want to supply morethan one script, you can use <SAMP>`;'</SAMP> as a command separator. Thefollowing two lines are equivalent, though the latter is cleaner:<P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>$ sed -e 's/foo/bar/g -e '12q' < infile > outfile$ sed 's/foo/bar/g;12q' < infile > outfile</pre></td></tr></table></P><P>Some portability zealots still go to great lengths to avoid <EM>heredocuments</EM> of more than twelve lines. The twelve line limit is actuallya limitation in some implementations of <CODE>sed</CODE>, which hasgradually seeped into the portable shell folklore as a general limit inall here documents. Autoconf, however, includes many here documentswith far more than twelve lines, and has not generated any complaintsfrom users. This is testament to the fact that at worst the limit isonly encountered in very obscure cases -- and most likely that it is nota real limit after all.</P><P>Also, be aware that branch labels of more than eight characters are notportable to some imPlementations of <CODE>sed</CODE>.</DL><P><BLOCKQUOTE><EM>Here documents</EM> are a way of redirecting literal strings into thestandard input of a command. You have certainly seen them before if youhave looked at other peoples shell scripts, though you may not haverealised what they were called:<P><TABLE width=100%><tr><td> </td><td class=example bgcolor=#6688aa><br><pre>cat >> /tmp/file$$ << _EOF_This is the text of a "here document"_EOF_</pre></td></tr></table></P><P></BLOCKQUOTE><P>Something else to be aware of is that the temporary files created byyour scripts can become a security problem if they are left in<TT>`/tmp'</TT> or if the names are predictable. A simple way around thisis to create a directory in <TT>`/tmp'</TT> that is unique to the processand owned by the process user. Some machines have a utility program forjust this purpose -- <CODE>mktemp -d</CODE> -- or else you can always fallback to <CODE>umask 077 && mkdir /tmp/$$</CODE>. Having created thisdirectory, all of the temporary files for this process should be writtento that directory, and its contents removed as soon as possible.</P><P>Armed with the knowledge of how to write shell code in a portablefashion as discussed in this chapter, in combination with the M4 detailsfrom the last chapter, the specifics of combining the two to write yourown Autoconf macros are covered in the next chapter.</P><P><A NAME="Writing New Macros for Autoconf"></A></TR></TABLE><BR> <FONT SIZE="-1">This document was generatedby <I>Gary V. Vaughan</I> on <I>September, 12 2004</I>using <A HREF="http://www.mathematik.uni-kl.de/~obachman/Texi2html"><I>texi2html</I></A></BODY></HTML>⌨️ 快捷键说明
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