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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 17] 17.20 grepping a Directory Tree (and a Gotcha) </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="1998-08-04T21:38:39Z"><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="ch17_01.htm"TITLE="17. Finding Files with find"><LINKREL="prev"HREF="ch17_19.htm"TITLE="17.19 Finding Files (Much) Faster with a find Database "><LINKREL="next"HREF="ch17_21.htm"TITLE="17.21 lookfor: Which File Has that Word? "></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="ch17_19.htm"TITLE="17.19 Finding Files (Much) Faster with a find Database "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 17.19 Finding Files (Much) Faster with a find Database "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 17<BR>Finding Files with find</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch17_21.htm"TITLE="17.21 lookfor: Which File Has that Word? "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 17.21 lookfor: Which File Has that Word? "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-1650">17.20 grepping a Directory Tree (and a Gotcha) </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-19646"></A><ACLASS="indexterm"NAME="AUTOID-19649"></A>Want to search every file, in some directory and all its subdirectories,to find the file that has a particular word or string in it?That's a job for<EMCLASS="emphasis">find</EM>and one of the<SPANCLASS="link"><EMCLASS="emphasis">grep</EM> (<ACLASS="linkend"HREF="ch27_01.htm#UPT-ART-7420"TITLE="Different Versions of grep ">27.1</A>)</SPAN>commands.</P><PCLASS="para">For example, to search all the files for lines starting with a numberand containing the words "SALE PRICE," you could use:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>egrep '^[0-9].*SALE PRICE' `find . -type f -print`</B></CODE>./archive/ad.1290: 1.99 a special SALE PRICE./archive/ad.0191: 2.49 a special SALE PRICE</PRE></BLOCKQUOTE></P><PCLASS="para"> Using the<SPANCLASS="link">backquotes (<ACLASS="linkend"HREF="ch09_16.htm"TITLE="Command Substitution ">9.16</A>)</SPAN>(<CODECLASS="literal">``</CODE>)might not work.If <EMCLASS="emphasis">find</EM> finds too many files, <EMCLASS="emphasis">egrep</EM>'scommand-line arguments can<SPANCLASS="link">get too long (<ACLASS="linkend"HREF="ch09_20.htm"TITLE="Too Many Files for the Command Line ">9.20</A>)</SPAN>.Using<ACLASS="indexterm"NAME="AUTOID-19665"></A><SPANCLASS="link"><EMCLASS="emphasis">xargs</EM> (<ACLASS="linkend"HREF="ch09_21.htm"TITLE="Handle Too-Long Command Lines with xargs ">9.21</A>)</SPAN>can solve that; it splits long sets of arguments into smaller chunks.There's a problem with that: if the last "chunk" has just one filenameand the <EMCLASS="emphasis">grep</EM> command finds a match there, <EMCLASS="emphasis">grep</EM> won't printthe filename:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"><ACLASS="co"HREF="ch27_06.htm"TITLE="27.6 Fast grep Isn't ">fgrep</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">% <CODECLASS="userinput"><B>find . -type f -print | xargs fgrep '$12.99'</B></CODE>./old_sales/ad.0489: Get it for only $12.99!./old_sales/ad.0589: Last chance at $12.99, this month!Get it for only $12.99 today.</PRE></TD></TR></TABLE></P><PCLASS="para">The answer is to add the UNIX "empty file,"<SPANCLASS="link"><EMCLASS="emphasis">/dev/null</EM> (<ACLASS="linkend"HREF="ch13_14.htm"TITLE="What Can You Do with an Empty File? ">13.14</A>)</SPAN>.It's a filename that's guaranteed never to match butalways to leave <EMCLASS="emphasis">fgrep</EM> with at least two filenames:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>find . -type f -print | xargs fgrep '$12.99' /dev/null</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">Then <EMCLASS="emphasis">xargs</EM> will run commands like:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">fgrep '$12.99' /dev/null ./afile ./bfile ...fgrep '$12.99' /dev/null ./archives/ad.0190 ./archives/ad.0290 ...fgrep '$12.99' /dev/null ./old_sales/ad.1289</PRE></BLOCKQUOTE></P><PCLASS="para">That trick is also good when you use a wildcard and only one file mightmatch it.<EMCLASS="emphasis">grep</EM> won't always print the file's name unless you add <EMCLASS="emphasis">/dev/null</EM>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>grep "<CODECLASS="replaceable"><I>whatever</I></CODE>" /dev/null /x/y/z/a*</B></CODE></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="ch17_19.htm"TITLE="17.19 Finding Files (Much) Faster with a find Database "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 17.19 Finding Files (Much) Faster with a find Database "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="ch17_21.htm"TITLE="17.21 lookfor: Which File Has that Word? 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