Program: tailwtmp (Perl Cookbook, 2nd Edition)

## 8.24. Program: tailwtmp

Every time a user logs into or out of a Unix system, a record is added to the wtmp file. You can't use the normal tail program on it, because the file is in binary format. The tailwtmp program in Example 8-7 knows the format of the binary file and shows every new record as it appears. You'll have to adjust the `pack` format for your own system.

#### Example 8-7. tailwtmp

>       #!/usr/bin/perl -w
>       # 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, "< :raw", "/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( );
>       }

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