#!/usr/bin/perl -w
use strict;

# tee program

$| =1; #sometimes important, flushes I/O for each write.

sub usage () 
{
   print "TEE USAGE:\n tees stdout to a file and to stdout\n".
      " program | tee outfile\n";
   exit(0);
}

my $filename = shift @ARGV;
usage unless $filename;

open (OUTFILE, ">$filename")
          or (die "Can't open OUTFILE: $!");

while (<>)
{
   print;
   print OUTFILE;
}