#!/usr/bin/perl --

use strict;
use warnings;

use File::Copy;
use File::Compare;

my @latex = qw'latex test.tex';    # !!perldoc -f system

system(@latex) == 0
  or die "system (@latex) failed:( $! ):( $? )";

copy(qw"test.log test-old.log")
  or die "Copy failed: $!";

system(@latex) == 0
  or die "system (@latex) failed:( $! ):( $? )";

while ( compare( "test.log", "test-old.log" ) ) {
    copy(qw"test.log test-old.log")
      or die "Copy failed: $!";

    system(@latex) == 0
      or die "system (@latex) failed:( $! ):( $? )";
}

exit 0;
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Note that File::Compare uses 2 arg open