huh? I've presented two ways of getting a child's output already! (qx// and open '-|')

Update: Here's a third way:

use IPC::Open2 qw( open2 );

sub line_count {
   my ($fname) = @_;
   my $pid = open2(my $fr_child, undef, 'cat', $fname) or die;
   1 while <$fr_child>;
   waitpid $pid, 0;
   return $.;
}
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 qx//
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That command will capture the output of any system command run. See also the "backticks" operator, which is identical to qx.

Why you think so?

my $fileName = '/some/path/to/file.ext';
my $returnVal = `wc -l $fileName`;
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No, you've merely hidden the opening of the file down inside an external utility. The file is still being opened and completely read, you've just managed to introduce a layer of indirection and a fork/exec overhead.

In order to count the number of lines in a file something is going to have to open the file and search through it for end-of-line markers. That is what he meant when said impossible.

(Of course if you were dealing with a file that used fixed-length lines that still were newline terminated you could cheat and do it with stat and /, but for all normal intents and purposes "impossible" is still a reasonable pronouncement. :)

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