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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 1] 1.5 Anyone Can Program the Shell </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="1998-08-04T21:30:58Z"><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="ch01_01.htm"TITLE="1. Introduction"><LINKREL="prev"HREF="ch01_04.htm"TITLE="1.4 Using Pipes to Create a New Tool "><LINKREL="next"HREF="ch01_06.htm"TITLE="1.6 Power Tools for Editing "></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="ch01_04.htm"TITLE="1.4 Using Pipes to Create a New Tool "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 1.4 Using Pipes to Create a New Tool "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 1<BR>Introduction</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch01_06.htm"TITLE="1.6 Power Tools for Editing "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 1.6 Power Tools for Editing "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-1003">1.5 Anyone Can Program the Shell </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-895"></A>One of the really wonderful things about the shell is that itdoesn't just read and execute the commands you type at a prompt.The shell is a complete programming language.</P><PCLASS="para">The ease of shell programming is one of the realhighlights of UNIX for novices.A shell program need be no more than a single complex commandline saved in a file - or a series of commands.</P><PCLASS="para">For example, let's say that you occasionally need to convert aMacintosh Microsoft Word file for use on your UNIX system.<ACLASS="indexterm"NAME="AUTOID-900"></A>Word lets you save the file in ASCII format. But there's acatch: the Macintosh uses a carriage return(<SPANCLASS="link">ASCII character 015 (<ACLASS="linkend"HREF="ch51_03.htm"TITLE="ASCII Characters: Listing and Getting Values ">51.3</A>)</SPAN>)to mark the end of each line, while UNIX uses a linefeed(ASCII 012). As a result, with UNIX, the file lookslike one long paragraph, with no end in sight.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-905"></A>That's easy to fix: the UNIX<SPANCLASS="link"><EMCLASS="emphasis">tr</EM> (<ACLASS="linkend"HREF="ch35_11.htm"TITLE="Hacking on Characters with tr ">35.11</A>)</SPAN>command can convert everyoccurrence of one character in a file to another:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>tr '\015' '\012' <</B></CODE> <CODECLASS="replaceable"><I>file.mac</I></CODE><CODECLASS="userinput"><B> > </B></CODE><CODECLASS="replaceable"><I>file.UNIX</I></CODE></PRE></BLOCKQUOTE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-917"></A><ACLASS="indexterm"NAME="AUTOID-920"></A><ACLASS="indexterm"NAME="AUTOID-922"></A>But you're a novice, and you don't want to remember thisparticular piece of magic. Fine. Save the first part ofthis command line in a file called <EMCLASS="emphasis">mac2UNIX</EM> in your<SPANCLASS="link">personal <EMCLASS="emphasis">bin</EM> directory (<ACLASS="linkend"HREF="ch04_02.htm"TITLE="A bin Directory for Your Programs and Scripts ">4.2</A>)</SPAN>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">tr '\015' '\012'</PRE></BLOCKQUOTE></P><PCLASS="para">Make the file executable with<SPANCLASS="link"><EMCLASS="emphasis">chmod</EM> (<ACLASS="linkend"HREF="ch22_07.htm"TITLE="Using chmod to Change File Permission ">22.7</A>)</SPAN>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>chmod +x mac2UNIX</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">Now you can say:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>mac2UNIX < </B></CODE><CODECLASS="replaceable"><I>file.mac</I></CODE><CODECLASS="userinput"><B> > </B></CODE><CODECLASS="replaceable"><I>file.UNIX</I></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">But say, why settle for that? What if you want to convert abunch of files at once? Easy. The shell includes a general<ACLASS="indexterm"NAME="AUTOID-945"></A><ACLASS="indexterm"NAME="AUTOID-948"></A><ACLASS="indexterm"NAME="AUTOID-950"></A>way of referring to arguments passed to a script, and a numberof looping constructs. The script:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"><ACLASS="co"HREF="ch44_16.htm"TITLE="44.16 Handling Command-Line Arguments with a for Loop ">for</A> <ACLASS="co"HREF="ch06_08.htm"TITLE="6.8 Shell Variables ">$x</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">for xdo echo "Converting $x" tr '\015' '\012' < "$x" > "tmp.$x" mv "tmp.$x" "$x"done</PRE></TD></TR></TABLE></P><PCLASS="para">will convert any number of files with one command, replacingeach original with the converted version:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>mac2UNIX</B></CODE> <CODECLASS="replaceable"><I>file1 file2 file3 ...</I></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">As you become more familiarwith UNIX, it quickly becomes apparent that doingjust a little homework can save hours of tedium.This script incorporates only two simple programming constructs: the<EMCLASS="emphasis">for</EM> loop<ACLASS="indexterm"NAME="AUTOID-964"></A><ACLASS="indexterm"NAME="AUTOID-966"></A>and<SPANCLASS="link">variable substitution (<ACLASS="linkend"HREF="ch06_08.htm"TITLE="Shell Variables ">6.8</A>, <ACLASS="linkend"HREF="ch06_01.htm#UPT-ART-1170"TITLE="What Environment Variables Are Good For ">6.1</A>)</SPAN>.As a new user, with no programmingexperience, I learned these two constructs by example: I saved a skeleton<EMCLASS="emphasis">for</EM> loop in a file and simplyfilled in the blanks with whatevercommands I wanted to repeat.</P><PCLASS="para">Simple shell programs like this did more for my feeling that computers couldautomate my work than anything since my first introduction to word processing.It made real sense of the line, "Let the computer do the dirty work."</P><PCLASS="para">In short, UNIX is sometimes difficult because it is so rich and complex.The user who doesn't want to learn the complexity doesn't have to - thebasic housekeeping commands are as simple as MS-DOS on the IBM PC.But the user who wants to take the time to investigate the possibilitiescan uncover a wealth of useful tools.</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">TOR</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="ch01_04.htm"TITLE="1.4 Using Pipes to Create a New Tool "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 1.4 Using Pipes to Create a New Tool "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="ch01_06.htm"TITLE="1.6 Power Tools for Editing "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 1.6 Power Tools for Editing "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">1.4 Using Pipes to Create a New Tool </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">1.6 Power Tools for Editing </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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