#! perl -slw
use strict;
use File::Slurp;
use Time::HiRes qw[ time ];

print STDERR time;
my $s = read_file( $ARGV[0], scalar_ref => 1 );
print STDERR time;
$$s =~s/\t/ /g ;
print STDERR time;
write_file( $ARGV[1], $s );
print STDERR time;

__END__
[22:14:07.81] C:\test>984648-2 500MB.csv junk.txt
1343769390.96321
1343769394.24913
1343769394.70982
Terminating on signal SIGINT(2)