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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 9] 9.7 String Editing in ksh and bash </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="1998-08-04T21:35:00Z"><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="ch09_01.htm"TITLE="9. Saving Time on the Command Line"><LINKREL="prev"HREF="ch09_06.htm"TITLE="9.6 String Editing (Colon) Operators "><LINKREL="next"HREF="ch09_08.htm"TITLE="9.8 Filename Completion: Faster Filename Typing "></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="ch09_06.htm"TITLE="9.6 String Editing (Colon) Operators "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 9.6 String Editing (Colon) Operators "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 9<BR>Saving Time on the Command Line</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch09_08.htm"TITLE="9.8 Filename Completion: Faster Filename Typing "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 9.8 Filename Completion: Faster Filename Typing "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-9915">9.7 String Editing in ksh and bash </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-10080"></A><ACLASS="indexterm"NAME="AUTOID-10083"></A><ACLASS="indexterm"NAME="AUTOID-10086"></A><ACLASS="indexterm"NAME="AUTOID-10089"></A>The C shell's<SPANCLASS="link">string editing operators (<ACLASS="linkend"HREF="ch09_06.htm"TITLE="String Editing (Colon) Operators ">9.6</A>)</SPAN>can be used with shell variables and, in some cases, with command history.Those operators also work with <EMCLASS="emphasis">bash</EM> history.But the Korn shell and <EMCLASS="emphasis">bash</EM> have a different way to edit shellvariables.<ACLASS="xref"HREF="ch09_07.htm#UPT-ART-9915-TAB-0"TITLE="ksh and bash String Editing Operators">Table 9.1</A> shows them:</P><TABLECLASS="table"><CAPTIONCLASS="table"><ACLASS="title"NAME="UPT-ART-9915-TAB-0">Table 9.1: ksh and bash String Editing Operators</A></CAPTION><THEADCLASS="thead"><TRCLASS="row"VALIGN="TOP"><THCLASS="entry"ALIGN="LEFT"ROWSPAN="1"COLSPAN="1">Operator</TH><THCLASS="entry"ALIGN="LEFT"ROWSPAN="1"COLSPAN="1">Explanation</TH></TR></THEAD><TBODYCLASS="tbody"><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">${<EMCLASS="emphasis">variable</EM>#<EMCLASS="emphasis">pattern</EM>}</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1"><PCLASS="para">Delete the shortest part of <EMCLASS="emphasis">pattern</EM> that matchesthe beginning of <EMCLASS="emphasis">variable</EM>'s value. Return the rest.</P></TD></TR><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">${<EMCLASS="emphasis">variable</EM>##<EMCLASS="emphasis">pattern</EM>}</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1"><PCLASS="para">Delete the longest part of <EMCLASS="emphasis">pattern</EM> that matchesthe beginning of <EMCLASS="emphasis">variable</EM>'s value. Return the rest.</P></TD></TR><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">${<EMCLASS="emphasis">variable</EM>%<EMCLASS="emphasis">pattern</EM>}</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1"><PCLASS="para">Delete the shortest part of <EMCLASS="emphasis">pattern</EM> that matchesthe end of <EMCLASS="emphasis">variable</EM>'s value.Return the rest.</P></TD></TR><TRCLASS="row"VALIGN="TOP"><TDCLASS="entry"ROWSPAN="1"COLSPAN="1">${<EMCLASS="emphasis">variable</EM>%%<EMCLASS="emphasis">pattern</EM>}</TD><TDCLASS="entry"ROWSPAN="1"COLSPAN="1"><PCLASS="para">Delete the longest part of <EMCLASS="emphasis">pattern</EM> that matchesthe end of <EMCLASS="emphasis">variable</EM>'s value.Return therest.</P></TD></TR></TBODY></TABLE><PCLASS="para">The <EMCLASS="emphasis">pattern</EM>s can be filename wildcard characters: <CODECLASS="literal">*</CODE>,<CODECLASS="literal">?</CODE>, and <CODECLASS="literal">[]</CODE>; with string editing operators,wildcards match strings in the same way they match filenames.(These are not <EMCLASS="emphasis">sed</EM>-like regular expressions.)The first two operators, with <CODECLASS="literal">#</CODE>, edit variables from the front.The other two, with <CODECLASS="literal">%</CODE>, edit from the end.Here's a system for remembering which does what:you put a number sign (<CODECLASS="literal">#</CODE>) at the <EMCLASS="emphasis">front</EM> of a numberand a percent sign (<CODECLASS="literal">%</CODE>) at the <EMCLASS="emphasis">end</EM> of a number.</P><PCLASS="para">Time for some examples.The variable <EMCLASS="emphasis">var</EM> contains <EMCLASS="emphasis">/a/b/c/d/e.f.g</EM>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen"><BCLASS="emphasis.bold">Expression</B> <BCLASS="emphasis.bold">Result</B>${var} /a/b/c/d/e.f.g${var#/*/} b/c/d/e.f.g${var##/*/} e.f.g${var%.*} /a/b/c/d/e.f${var%%.*} /a/b/c/d/e${var%%/*/} /a/b/c/d/e.f.g${var%%/*}${var%/b*} /a${var%%/b*} /a</PRE></BLOCKQUOTE></P><PCLASS="para">How about a practical example?The<ACLASS="indexterm"NAME="AUTOID-10157"></A><SPANCLASS="link"><EMCLASS="emphasis">PATH</EM> variable (<ACLASS="linkend"HREF="ch06_04.htm"TITLE="The PATH Environment Variable ">6.4</A>)</SPAN>is a string separated by colons (<CODECLASS="literal">:</CODE>).Let's say you want to remove the last directory from the system pathand add <CODECLASS="literal">$HOME/bin</CODE> in place of the last directory.You'd type this command, or put a line like this in your <EMCLASS="emphasis">.profile</EM>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">PATH=${PATH%:*}:$HOME/bin</PRE></BLOCKQUOTE></P><PCLASS="para">Because the <CODECLASS="literal">${PATH%:*}</CODE> has a single <CODECLASS="literal">%</CODE>,that operator removes the least it can:just the last colon plus the directory name after it.After string editing, the rest of the <EMCLASS="emphasis">PATH</EM> has<CODECLASS="literal">:$HOME/bin</CODE> appended to it.The new value is saved as the new <EMCLASS="emphasis">PATH</EM>.</P><PCLASS="para">The Bourne shell's<SPANCLASS="link">parameter substitution operators (<ACLASS="linkend"HREF="ch45_12.htm"TITLE="Parameter Substitution ">45.12</A>)</SPAN>look similar, but they're mostly useful for shell programming.</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="ch09_06.htm"TITLE="9.6 String Editing (Colon) Operators "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 9.6 String Editing (Colon) Operators "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 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