#!C:\perl\bin\perl.exe
# file_compare.pl
# Purpose: compare two files and show differences

use strict;
use warnings;

my $file1 ='E:\files\file_1.txt' or die "filename missing \n";
my $file2 = 'E:\files\file_2.txt' or die "filename missing \n";

open (FILE1, "< $file1") or die "Can not read file $file1: $! \n";
my @file1_contents = <FILE1>; # read entire contents of file
close (FILE1);

open (FILE2, "< $file2") or die "Can not read file $file2: $! \n";
my @file2_contents = <FILE2>; # read entire contents of file
close (FILE2);

my $length1 = $#file1_contents; # number of lines in first file
my $length2 = $#file2_contents; # number of lines in second file

if ($length1 > $length2) {
# first file contains more lines than second file
my $counter2 = 0;
foreach my $line_file1 (@file1_contents) {
chomp ($line_file1);

if (defined ($file2_contents[$counter2])) {
# line exists in second file
chomp (my $line_file2 = $file2_contents[$counter2]);

if ($line_file1 ne $line_file2) {
print "\nline " . ($counter2 + 1) . " \n";
print "< $line_file1 \n" if ($line_file1 ne ""); 
print "--- \n";
print "> $line_file2 \n\n" if ($line_file2 ne "");
}
}
else {
# there is no line in second file
print "\nline " . ($counter2 + 1) . " \n";
print "< $line_file1 \n" if ($line_file1 ne ""); 
print "--- \n";
print "> \n"; # this line does not exist in file2
}
$counter2++; # point to the next line in file2
}
}
else {
# second file contains more lines than first file
# or both have equal number of lines
my $counter1 = 0;
foreach my $line_file2 (@file2_contents) {
chomp ($line_file2);

if (defined ($file1_contents[$counter1])) {
# line exists in first file
chomp (my $line_file1 = $file1_contents[$counter1]);

if ($line_file1 ne $line_file2) {
print "\nline " . ($counter1 + 1) . " \n";
print "< $line_file1 \n" if ($line_file1 ne "");
print "--- \n";
print "> $line_file2 \n" if ($line_file2 ne "");
}
}
else {
# there is no line in first file
print "\nline " . ($counter1 + 1) . " \n";
print "< \n"; # this line does not exist in file1
print "--- \n";
print "> $line_file2 \n" if ($line_file2 ne "");
}
$counter1++; # point to next line in file1
}
}