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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 45] 45.35 Using a Control Character in a Script </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="1998-08-04T21:55:19Z"><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="ch45_01.htm"TITLE="45. Shell Programming for the Initiated"><LINKREL="prev"HREF="ch45_34.htm"TITLE="45.34 Arrays in the Bourne Shell "><LINKREL="next"HREF="ch45_36.htm"TITLE="45.36 Shell Lockfile "></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="ch45_34.htm"TITLE="45.34 Arrays in the Bourne Shell "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 45.34 Arrays in the Bourne Shell "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 45<BR>Shell Programming for the Initiated</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch45_36.htm"TITLE="45.36 Shell Lockfile "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 45.36 Shell Lockfile "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-7882">45.35 Using a Control Character in a Script </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55157"></A><ACLASS="indexterm"NAME="AUTOID-55160"></A>There are times when you need to use non-printing control charactersin a script file.If you type them directly into the file, they can be invisible toprinters and on your screen - or, worse, they can cause trouble whenyou print or display the file.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55164"></A>One time you might need to store control characters in a scriptis when you're writing <EMCLASS="emphasis">sed</EM> substitution commands; youdon't know what delimiters to use because the strings you'resubstituting could contain almost any text:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">sed "s/$something/$whoknows/"</PRE></BLOCKQUOTE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55171"></A>Because<SPANCLASS="link"><EMCLASS="emphasis">sed</EM> can use almost any character as the delimiter (<ACLASS="linkend"HREF="ch34_07.htm"TITLE="Delimiting a Regular Expression ">34.7</A>)</SPAN>,you canuse a control character like CTRL-a instead of the slash (<CODECLASS="literal">/</CODE>).Another time you might also need to use non-printable strings of charactersis for controlling a terminal; you won't want to type an Escape characterdirectly into the file.</P><PCLASS="para">The answer is to use a command that will create the control charactersas the script runs - and store them in shell variables.</P><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="UPT-ART-7882-SECT-1.1">45.35.1 With echo </A></H3><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55181"></A><ACLASS="indexterm"NAME="AUTOID-55184"></A><ACLASS="indexterm"NAME="AUTOID-55187"></A>If<SPANCLASS="link">your version of <EMCLASS="emphasis">echo</EM> (<ACLASS="linkend"HREF="ch08_06.htm"TITLE="Output Command-Line Arguments ">8.6</A>, <ACLASS="linkend"HREF="ch46_10.htm"TITLE="A Portable echo Command ">46.10</A>)</SPAN>interprets an octal number in astring like <CODECLASS="literal">\001</CODE> as its<SPANCLASS="link">ASCII value (<ACLASS="linkend"HREF="ch51_03.htm"TITLE="ASCII Characters: Listing and Getting Values ">51.3</A>)</SPAN>,the job is easy.An octal-to-ASCII chart shows you that 001 is CTRL-a.You can store the output of <EMCLASS="emphasis">echo</EM> in a shell variable,and use the variable wherever you need a CTRL-a character:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"><ACLASS="co"HREF="ch09_16.htm"TITLE="9.16 Command Substitution ">`...`</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">ca=`echo '\001'` # control-A character ...sed "s${ca}$something${ca}$whoknows${ca}"</PRE></TD></TR></TABLE></P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="UPT-ART-7882-SECT-1.2">45.35.2 With tr and echo </A></H3><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55201"></A><ACLASS="indexterm"NAME="AUTOID-55204"></A>If your <EMCLASS="emphasis">echo</EM> can't make control characters directly, the <EMCLASS="emphasis">tr</EM>utility can do it for you.<EMCLASS="emphasis">tr</EM> understands octal sequences, too.Make your <EMCLASS="emphasis">echo</EM> output characters you don't want, and have <EMCLASS="emphasis">tr</EM>translate them into the control characters you do want.For example, to make the 4-character sequence<EMCLASS="emphasis">ESCape CTRL-a [ CTRL-w</EM>,use a command like this:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">escseq=`echo 'ea[w' | tr 'eaw' '\033\001\027'`</PRE></BLOCKQUOTE></P><PCLASS="para"><EMCLASS="emphasis">tr</EM> reads the four characters down the pipe from <EMCLASS="emphasis">echo</EM>;it translates the <EMCLASS="emphasis">e</EM> into ESCape (octal 033),the <EMCLASS="emphasis">a</EM> into CTRL-a (octal 001),and the <EMCLASS="emphasis">w</EM> into CTRL-w (octal 027).The left bracket isn't changed; <EMCLASS="emphasis">tr</EM> prints it as is.</P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-55223"></A><ACLASS="indexterm"NAME="AUTOID-55226"></A>The <EMCLASS="emphasis">script.tidy</EM> script in article<ACLASS="xref"HREF="ch51_06.htm"TITLE="Cleaning script Files ">51.6</A>shows a way to set several control characters in several shell variableswith one command - that's efficient because it cuts the number ofsubprocesses needed.Another way to get control characters is with the handy<SPANCLASS="link"><EMCLASS="emphasis">jot</EM> (<ACLASS="linkend"HREF="ch45_11.htm"TITLE="The Multipurpose jot Command ">45.11</A>)</SPAN>command on the CD-ROM.</P></DIV><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="ch45_34.htm"TITLE="45.34 Arrays in the Bourne Shell "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 45.34 Arrays in the Bourne Shell "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="ch45_36.htm"TITLE="45.36 Shell Lockfile "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 45.36 Shell Lockfile "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">45.34 Arrays in the Bourne Shell </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">45.36 Shell Lockfile </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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