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<HTML><HEAD><TITLE>Recipe 8.10. Removing the Last Line of a File (Perl Cookbook)</TITLE><METANAME="DC.title"CONTENT="Perl Cookbook"><METANAME="DC.creator"CONTENT="Tom Christiansen & Nathan Torkington"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1999-07-02T01:38:46Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-243-3"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="ch08_01.htm"TITLE="8. File Contents"><LINKREL="prev"HREF="ch08_10.htm"TITLE="8.9. Processing Variable-Length Text Fields"><LINKREL="next"HREF="ch08_12.htm"TITLE="8.11. Processing Binary Files"></HEAD><BODYBGCOLOR="#FFFFFF"><img alt="Book Home" border="0" src="gifs/smbanner.gif" usemap="#banner-map" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Perl Cookbook"><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><p><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch08_10.htm"TITLE="8.9. Processing Variable-Length Text Fields"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 8.9. Processing Variable-Length Text Fields"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch08_01.htm"TITLE="8. File Contents"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch08_12.htm"TITLE="8.11. Processing Binary Files"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 8.11. Processing Binary Files"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch08-chap08_removing_0">8.10. Removing the Last Line of a File</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch08-pgfId-1012">Problem<ACLASS="indexterm"NAME="ch08-idx-1000004671-0"></A><ACLASS="indexterm"NAME="ch08-idx-1000004671-1"></A><ACLASS="indexterm"NAME="ch08-idx-1000004671-2"></A></A></H3><PCLASS="para">You'd like to remove the last line from a file.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch08-pgfId-1018">Solution</A></H3><PCLASS="para">Read the file a line at a time and keep track of the byte address of the last line you've seen. When you've exhausted the file, truncate to the last address you saved:</P><PRECLASS="programlisting">open (FH, "+< $file") or die "can't update $file: $!";while ( <FH> ) { $addr = tell(FH) unless eof(FH);}truncate(FH, $addr) or die "can't truncate $file: $!";</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch08-pgfId-1034">Discussion</A></H3><PCLASS="para">This is much more efficient than reading the file into memory all at once, since it only holds one line at a time. Although you still have to grope your way through the whole file, you can use this program on files larger than available memory.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch08-pgfId-1040">See Also</A></H3><PCLASS="para">The <CODECLASS="literal">open</CODE> and <CODECLASS="literal">binmode</CODE> functions in <ICLASS="filename">perlfunc </I>(1) and in <ACLASS="olink"HREF="../prog/ch03_01.htm">Chapter 3</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A>; your system's <ICLASS="filename">open </I>(2) and <ICLASS="filename">fopen</I> (3) manpages</P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch08_10.htm"TITLE="8.9. Processing Variable-Length Text Fields"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 8.9. 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