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

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

__END__

[21:35:14.40] C:\test>984648-1 500MB.csv junk.txt
1343767102.78642
1343767106.4356
1343767106.89558
Terminating on signal SIGINT(2)