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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 25] 25.20 Printing the Top of a File </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="1998-08-04T21:43:31Z"><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="ch25_01.htm"TITLE="25. Showing What's in a File"><LINKREL="prev"HREF="ch25_19.htm"TITLE="25.19 Reverse Lines in Long Files with flip "><LINKREL="next"HREF="ch25_21.htm"TITLE="25.21 Numbering Lines "></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="ch25_19.htm"TITLE="25.19 Reverse Lines in Long Files with flip "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 25.19 Reverse Lines in Long Files with flip "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 25<BR>Showing What's in a File</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch25_21.htm"TITLE="25.21 Numbering Lines "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 25.21 Numbering Lines "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-2670">25.20 Printing the Top of a File </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-28171"></A><ACLASS="indexterm"NAME="AUTOID-28173"></A>Many versions of BSD UNIX include a nice program called <EMCLASS="emphasis">head</EM> thatprints the top<EMCLASS="emphasis">n</EM> (default: 10) lines of a file.System V or other users without <EMCLASS="emphasis">head</EM> canemulate its behavior with <EMCLASS="emphasis">sed</EM>.</P><PCLASS="para">The easiest way is simply to use <SPANCLASS="link"><EMCLASS="emphasis">sed</EM>'s <EMCLASS="emphasis">q</EM> command (<ACLASS="linkend"HREF="ch34_21.htm"TITLE="Uses of the sed Quit Command ">34.21</A>)</SPAN>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>sed 10q </B></CODE><CODECLASS="replaceable"><I>file</I></CODE></PRE></BLOCKQUOTE></P><TABLECLASS="para.programreference"BORDER="1"><TR><THVALIGN="TOP"><ACLASS="programreference"HREF="examples/index.htm"TITLE="head">head</A><BR></TH><TDVALIGN="TOP"> If you want to get fancy, you can use a shell scriptto emulate all of the behavior of the BSD <EMCLASS="emphasis">head</EM>command, including taking an option for the number of lines to beprinted, and printing a separator line if multiple filenames arespecified on the same command line.</TD></TR></TABLE><PCLASS="para">The CD-ROM has that script.Most of it is straightforward.One interesting part is shown below.It's the <EMCLASS="emphasis">sed</EM> command that prints the separator when more than onefile is shown:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">sed "1i\\==> $1 <==${show}q" $1</PRE></BLOCKQUOTE></P><PCLASS="para">The <EMCLASS="emphasis">sed</EM> command <EMCLASS="emphasis">1i</EM> inserts the separator before line 1.The <EMCLASS="emphasis">sed</EM> command <EMCLASS="emphasis">q</EM> quits after the number of lines(by default, 10) in the <CODECLASS="literal">$show</CODE> <SPANCLASS="link">shell variable (<ACLASS="linkend"HREF="ch06_08.htm"TITLE="Shell Variables ">6.8</A>)</SPAN>.The shell substitutes <CODECLASS="literal">$1</CODE> with the filename being read.The double quotes (<CODECLASS="literal">"</CODE>) around the <EMCLASS="emphasis">sed</EM> commands let theshell build the commands on-the-fly before starting <EMCLASS="emphasis">sed</EM>.</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">JP</SPAN>, <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="ch25_19.htm"TITLE="25.19 Reverse Lines in Long Files with flip "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 25.19 Reverse Lines in Long Files with flip "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="ch25_21.htm"TITLE="25.21 Numbering Lines "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 25.21 Numbering Lines "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">25.19 Reverse Lines in Long Files with flip 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