Shell Programming and Scripting

die "Usage infile outfile reGex" if @ARGV != 3;
($regex) = @ARGV;

open(F,$ARGV[0]) or die "Can't open";
open(FOUT,"+>$ARGV[1]") or die "Can't open";

while (<F>)
{
  print FOUT if /$regex/.../$regex/;
}

($regex) = @ARGV;

die "Usage infile outfile reGex" if @ARGV != 3;
($regex) = $ARGV[2];
open(F,$ARGV[0]) or die "Can't open";
open(FOUT,"+>$ARGV[1]") or die "Can't open";
while (<F>)
{
  # $_ is a default variable
  # if your regex match the line you get the line into $ARGV[1] file
  print FOUT "$_" if ($_ =~ /$regex/);
}