FAQ 5.3 How do I count the number of lines in a file?

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5.3: How do I count the number of lines in a file?

(contributed by brian d foy)

Conceptually, the easiest way to count the lines in a file is to simply
read them and count them:

my $count = 0;
while( <$fh> ) { $count++; }

You don't really have to count them yourself, though, since Perl already
does that with the $. variable, which is the current line number from
the last filehandle read:

1 while( <$fh> );
my $count = $.;

If you want to use $., you can reduce it to a simple one-liner, like one
of these:

% perl -lne '} print $.; {' file

% perl -lne 'END { print $. }' file

Those can be rather inefficient though. If they aren't fast enough for
you, you might just read chunks of data and count the number of
newlines:

my $lines = 0;
open my($fh), '<:raw', $filename or die "Can't open $filename: $!";
while( sysread $fh, $buffer, 4096 ) {
$lines += ( $buffer =~ tr/\n// );
}
close FILE;

However, that doesn't work if the line ending isn't a newline. You might
change that "tr///" to a "s///" so you can count the number of times the
input record separator, $/, shows up:

my $lines = 0;
open my($fh), '<:raw', $filename or die "Can't open $filename: $!";
while( sysread $fh, $buffer, 4096 ) {
$lines += ( $buffer =~ s|$/||g; );
}
close FILE;

If you don't mind shelling out, the "wc" command is usually the fastest,
even with the extra interprocess overhead. Ensure that you have an
untainted filename though:

#!perl -T

$ENV{PATH} = undef;

my $lines;
if( $filename =~ /^([0-9a-z_.]+)\z/ ) {
$lines = `/usr/bin/wc -l $1`
chomp $lines;
}



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