Yesterday, I had to pick out the last 100 lines in a file, for a small log viewer I was writing. Neither the Perl FAQ nor the Perl Cookbook had quite the right answer. So, this is what I ended up with.
sub last_lines {
my ( $fh, $howmany ) = @_;
my ( @lines, $i );
while ( <$fh> ) {
chomp;
$lines[ $i++ ] = $_;
$i = 0 if $i == $howmany;
}
return grep { defined }
@lines[ $i .. $howmany - 1 ], @lines[ 0 .. $i - 1 ];
}
This is reasonably memory efficient, more so than the example I found which read the entire file in and then just picked the last $howmany items from the array.
The last line is interesting. We have to “swivel” the array around a partition point, in order to get the entries into the correct order. Also, we have to get rid of undefined entries. These crop up if you have less than $howmany lines in the file.
Jabbering Giraffe 
4 replies on “Last 100 lines in a file”
Engh. View source on the page for the formatting. You get the idea.
Errk, how convoluted.
<code>
sub last_lines {
my ( $fh, $howmany ) = @_;
my @lines;
while ( <$fh> ) {
chomp;
push @lines, $_;
shift @lines if @lines > $howmany;
}
return @lines;
}
</code>
Also, a lengthy treatise on this issue:
http://www.perlmonks.org/index.pl?node_id=162034
Thanks, Aristotle, that’s a much better idea! I’ve started doing that instead now.
BTW, the comment formatting should be using textile…