UNIX for Dummies Questions & Answers

#!/usr/bin/perl

use strict;
use warnings;

my %MON=qw(JAN 1 FEB 2 MAR 3 APR 4 MAY 5 JUN 6 JUL 7 AUG 8 SEP 9 OCT 10 NOV 11 DEC 12);
sub iso_date{
        my $date=shift;
        #Oracle style date
        $date=~s/(\d{2})-([A-Z]{3})-(\d{2})/sprintf "20%02d-%02d-%02d",$3, $MON{$2},$1/eg;
        #dd-mm-yyyy
        $date=~s/(\d{2})-(\d{2})-(\d{4})/$3-$2-$1/;
        #midnight datestamp
        $date=~s/(\d{4})(\d{2})(\d{2})0*/$1-$2-$3/;
        #USian mm/dd/yy
        $date=~s/(\d{2})\/(\d{2})\/(\d{2})/20$3-$2-$1/;
        return $date;
}
open (my $in_file , '<', $ARGV[0]);
open (my $new_file,'>',"$ARGV[0].tmp");
while (<$in_file>){
        my @rec=split(/\|/,$_);
        @date_fields=qw(0 11 24);
        for my $date_field ((@date_fields)){
                $rec[$date_field] = iso_date($rec[$date_field]);
        }
        print $new_file (join"\t",@rec);
}
rename("$ARGV[0].tmp","$ARGV[0]");