Compare Binary Files

[drodinthe559]

What should I use to compare two binary files? It appear File::Compare will compare text files. I tried using Test::BinaryData but it didn't work for me. Your help would be appreciated. Thanks, David

[ikegami]

If you're just trying to see if they are different:

open(my $fh1, '<', $file1) or die $!;
binmode($fh1);

open(my $fh2, '<', $file2) or die $!;
binmode($fh2);

local $/ = \(64*1024);  # Tweak as desired.
for (;;) {
   my $blk1 = <$fh1>;
   my $blk2 = <$fh2>;

   last if !defined($blk1) && !defined($blk2);

   die("diff\n")
      if !defined($blk1)
      || !defined($blk2)
      || $blk1 ne $blk2;
}

Might want to save time by pre-checking the size of the files.

It would be trivial to modify this code to output the bytes that differ.

Detecting insertions and deletions is a whole other story, though.

[Khen1950fx]

Diff::LibXDiff does a binary diff. It's also the diff engine used by git.

[morgon]

If all you want is to check whether the files have identical content or not I would simply compare the MD5 (or SHA-1) hashes.

Hash::MD5 will calculate the hash for you.

[ikegami]

Why? It seems to me that reading entire file to calculate its hashes is a waste of time compared to just reading the entire file.

Calculating hashes is useful in two circumstances: 1) When comparing one document to many (or many to many), 2) When a compact signature of the file is needed (for ease of communication or storage).

[pemungkah]

sub files_differ {
  system "cmp file1 file2";
 return $? >> 8;
}

If you're not comparing hundreds of files, this will do fine. Remember "the simplest thing that could possibly work"? This is it. Plus cup gives you the option to skip a certain number of bytes before starting the compare and a lot of other options. (Tip of the hat to MJD, who talked about this in detail in Twelve Views of Mark-Jason Dominus.

[afoken]

sub files_differ {
  system "cmp file1 file2";
 return $? >> 8;
}

Windows has no "cmp" command. $? is set to 0x0100, files_differ always returns 1, even with missing files, even with identical files. Instant fail.

H:\>perl -e "system 'cmp file1 file2';print $?,' ',$? >> 8"
'cmp' is not recognized as an internal or external command,
operable program or batch file.
256 1
H:\>

And by the way: Omitting quotes around the file name begs for trouble as soon as you replace the constants with variables. Using the multiple argument form of system would prevent that problem.

Alexander

[BrowserUk]

I have a cmp command on my windows system. There is also the comp command which has been available on all versions of windows:

C:\test>cmp
cmp: missing operand
cmp: Try `cmp --help' for more information.

C:\test>comp /?
Compares the contents of two files or sets of files.

COMP [data1] [data2] [/D] [/A] [/L] [/N=number] [/C] [/OFF[LINE]]

  data1      Specifies location and name(s) of first file(s) to compar
+e.
  data2      Specifies location and name(s) of second files to compare
+.
  /D         Displays differences in decimal format.
  /A         Displays differences in ASCII characters.
  /L         Displays line numbers for differences.
  /N=number  Compares only the first specified number of lines in each
+ file.
  /C         Disregards case of ASCII letters when comparing files.
  /OFF[LINE] Do not skip files with offline attribute set.

To compare sets of files, use wildcards in data1 and data2 parameters.

[pemungkah]

Quite agree on the list form invocation; that's a much better choice. I always forget it, for some reason.

Re no cmp on Windows: that just means this isn't the simplest possible thing for Windows. I'm sure there is an equivalent.

[zentara]

Finding differences in binary files might interest you.