Are you talking about the unix/gnu diff tool? How did you use it, and in what sense did it not work? Given two files, if they are different, diff will report what the differences are, and will return an exit status of 1 if the files differ, or 0 (="success") if they are identical.

If you don't want to see all the lines that differ, you can use the "cmp" command instead; it gives the same exit status as diff does, but will otherwise be fairly quiet, and will will only read all of its two input files when they happen to be identical (i.e. it stops as soon as it sees a difference). Examples:

cmp file1 file2 && echo same
cmp file1 file2 || echo different
[download]

(Identical checksums is not a guarantee of identical content, different checksums definitely indicate different content. You only need to run cmp on pairs that have the same checksum, to confirm whether they are really identical.)

I tried using diff but it did't work

Strange, your copy must be broken because this is exactly what diff does. And it will be far faster than any perl solution,

Or maybe you just used it wrong?

By just checking the file sizes, this will work a lot of the time to differentiate the two files:

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

my $file1     = "2006.txt";
my $file2     = "2007.txt";
my $file1size = -s $file1;
my $file2size = -s $file2;

print "The files have ", $file1size == $file2size ? "the same" : "diff
+erent", 
  " size.\n\n";
[download]

In what way did diff not work? Diff should be able to do exactly what you're trying to do...

If the files are very large and the differences are very early, you're going to spend a lot of time reading through a lot of file that you don't need to. Otherwise, this is a very easy way to find that files are different.

But if the only differences are near the end, then you'll waste a lot of time going through the file a line at the time. Worse: if the files are equal, then you'll have to go through the whole file anyway.

Why do people always suppose you'll commonly get positive results near the start of the loop count?

Let's make a compromise: select and read a random block from both files, somewhere "in the middle", and compare. If the files are different, then you'll likely see it immediately, especially if the typical differences are in the addition or deletion of whole lines, and not replacement of single characters.

This should work for any number of files, up to the maximum you can have open.

use List::Util qw( first );

my @files = ( 'FILE1', 'FILE2' );

my @handles;
foreach my $file ( @files ) {
    open my $fh, '<', $file or die "Can't read $file: $!";
    push @handles, $fh;
}

my $first_handle = shift @handles;

while ( my $line = <$first_handle> ) {
    if ( defined first { $line ne <$_> } @handles ) {
        die "There's a difference.";
    }
}
[download]

From win32 command prompt:

C:\>help fc
Compares two files or sets of files and displays the differences betwe
+en
them


FC [/A] [/C] [/L] [/LBn] [/N] [/OFF[LINE]] [/T] [/U] [/W] [/nnnn]
   [drive1:][path1]filename1 [drive2:][path2]filename2
FC /B [drive1:][path1]filename1 [drive2:][path2]filename2

  /A         Displays only first and last lines for each set of differ
+ences.
  /B         Performs a binary comparison.
  /C         Disregards the case of letters.
  /L         Compares files as ASCII text.
  /LBn       Sets the maximum consecutive mismatches to the specified
             number of lines.
  /N         Displays the line numbers on an ASCII comparison.
  /OFF[LINE] Do not skip files with offline attribute set.
  /T         Does not expand tabs to spaces.
  /U         Compare files as UNICODE text files.
  /W         Compresses white space (tabs and spaces) for comparison.
  /nnnn      Specifies the number of consecutive lines that must match
             after a mismatch.
  [drive1:][path1]filename1
             Specifies the first file or set of files to compare.
  [drive2:][path2]filename2
             Specifies the second file or set of files to compare.
[download]