open FILE, "file.txt";
my $count;
while (<FILE>) {
  $count++ unless /\S+/;
}
close FILE;
print $count;
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This is the best solution I would use, though /\S/ is sufficient.

Just as a footnote, if you do not want to count lines that contain a tab or some other such whitespace, you can substitue /\S+/ with /^$/ in either this code or in Fastolife's below

perl -ne '$count++ unless /\S/; print "$count\n" if eof' <filename
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A slightly shorter version perl -pe '$c++ unless /\S/}{$_=$c' Cheers,
Random.

Or, on *NIX systems,

shell prompt>grep -c '^[:blank:]*$' foo.bar
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-c tells grep to merely count lines which match the pattern (0 or more blanks between the beginning and end of the line)

Philosophy can be made out of anything. Or less -- Jerry A. Fodor

grep -vc '[^[:space:]]' filenames...
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Of course it isn't perl but it is sexy =) Tho to be honest I really use a space and ^Vtab rather than that crappy ansi notation =).

Someone needs to snag the most recent regexp engine from perl and make a real greperl or grep with a -P flag to use that engine. Too many good tweaks in the perl regexp are going unexercised. =)

--
$you = new YOU;
honk() if $you->love(perl)

That would be the hard way. Just grab tchrist's and Nick Ing-Simmons's greps writtin in Perl.

        - tye (but my friends call me "Tye")

There is all kinds of hard in the world:

root# ls -l `which perl`
-rwxr-xr-x    3 root     root       733687 Apr 15  2000 /usr/bin/perl
root# ls -l `which grep`
-rwxr-xr-x    1 root     root        75600 Feb  3  2000 /bin/grep

One of them is footprint. I love perl, but it's a big stick to hit grep with. =)

--
$you = new YOU;
honk() if $you->love(perl)