#!/usr/bin/perl

my $file='test.txt';
my $txt=join("\n",map{rand(1000)}(1..1000000));

open(my $fh, '>', $file) or die("$file $!");
print $fh $txt;
exec(q Xperl -le 'open($fh, q(<), $ARGV[0]) or die(qq($ARGV[0] $!)); $i=0; while(<$fh>){$i++}; print $i' -- X.$file);