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<HTML><HEAD><TITLE>Recipe 8.18. Program: tailwtmp (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="1999-07-02T01:38:56Z"><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_18.htm"TITLE="8.17. Testing a File for Trustworthiness"><LINKREL="next"HREF="ch08_20.htm"TITLE="8.19. Program: tctee"></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_18.htm"TITLE="8.17. Testing a File for Trustworthiness"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 8.17. Testing a File for Trustworthiness"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_20.htm"TITLE="8.19. Program: tctee"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 8.19. Program: tctee"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch08-10269">8.18. Program: tailwtmp</A></H2><PCLASS="para"><ACLASS="indexterm"NAME="ch08-idx-1000004729-0"></A><ACLASS="indexterm"NAME="ch08-idx-1000004729-1"></A><ACLASS="indexterm"NAME="ch08-idx-1000004729-2"></A><ACLASS="indexterm"NAME="ch08-idx-1000004729-3"></A>Every time a user logs into or out of a Unix system, a record is added to the <EMCLASS="emphasis">wtmp</EM> file. You can't use the normal <EMCLASS="emphasis">tail</EM> program on it because it's in binary format. The <ICLASS="filename">tailwtmp</I> program in <ACLASS="xref"HREF="ch08_19.htm#ch08-17356"TITLE="tailwtmp">Example 8.7</A> knows the format of the binary file and shows every new record as it appears. You'll have to adjust the <CODECLASS="literal">pack</CODE> format for your own system.</P><DIVCLASS="example"><H4CLASS="example"><ACLASS="title"NAME="ch08-17356">Example 8.7: tailwtmp</A></H4><PRECLASS="programlisting">#!/usr/bin/perl# tailwtmp - watch for logins and logouts; # uses linux utmp structure, from utmp(5)$typedef = 's x2 i A12 A4 l A8 A16 l';$sizeof = length pack($typedef, () );use IO::File;open(WTMP, '/var/log/wtmp') or die "can't open /var/log/wtmp: $!";seek(WTMP, 0, SEEK_END);for (;;) { while (read(WTMP, $buffer, $sizeof) == $sizeof) { ($type, $pid, $line, $id, $time, $user, $host, $addr) = unpack($typedef, $buffer); next unless $user && ord($user) && $time; printf "%1d %-8s %-12s %2s %-24s %-16s %5d %08x\n", $type,$user,$line,$id,scalar(localtime($time)), $host,$pid,$addr; } for ($size = -s WTMP; $size == -s WTMP; sleep 1) {} WTMP->clearerr();}</PRE></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_18.htm"TITLE="8.17. 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