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You mean something like:

#!/usr/bin/perl use strict; use warnings; use IO::Compress::Gzip qw(gzip); my ( $f1, $f2 ) = @ARGV[ 0 .. 1 ]; my %comparison; # Get file contents, and compute gzipped lengths. for my $file ( $f1, $f2 ) { get_content( $file, \%{ $comparison{$file} } ); computations( \%{ $comparison{$file} } ); } # Try both orderings of files to determine which produces # better results. The content is not needed after lengths # have been computed. $comparison{test1}{content} = $comparison{$f1}{content} . $comparison{$f2}{content}; computations( \%{ $comparison{test1} } ); delete $comparison{test1}{content}; $comparison{test2}{content} = $comparison{$f2}{content} . $comparison{$f1}{content}; computations( \%{ $comparison{test2} } ); delete $comparison{test2}{content}; # The original content is no longer needed. foreach my $file ( $f1, $f2 ) { delete $comparison{$file}{content}; } printf qq{Comparison: %5.2f%% similarity\n}, compute_ratio( \%comparison, ( $f1, $f2 ) ); sub order_pair { my ( $i, $j ) = @_; my ( $min, $max ) = ( $i, $j ); ( $min, $max ) = ( $max, $min ) if ( $max < $min ); return ( $min, $max ); } sub compute_ratio { my ( $hash, @fl ) = @_; my ( $min, $min_result, $max, $ratio ); ( $min_result, undef ) = order_pair( $hash->{test1}{gzip_length}, $hash->{test2}{gzip_length} ); ( $min, $max ) = order_pair( $hash->{ $fl[0] }{gzip_length}, $hash->{ $fl[1] }{gzip_length} ); # Files are 100% if they match exactly. # (a + b - a) / b = b / b = 1 # Files are 0% if they do not match exactly. # (a + b - (a+b)) / b = 0 / b = 0 # Ratio computed as how close to the minimal size $ratio = 100.0 * ( $min + $max - $min_result ) / $max; return $ratio; } sub computations { my ($hash) = @_; # Compute gzipped length of content $hash->{length} = length $hash->{content}; gzip \$hash->{content}, \$hash->{compressed}; # Gzipped content not needed # after length has been computed. $hash->{gzip_length} = length $hash->{compressed}; delete $hash->{compressed}; } sub get_content { my ( $fn, $hash ) = @_; # Slurp in file content in bin mode open( DF, $fn ) or die $!; binmode DF; $/ = undef; $hash->{content} = <DF>; close DF; }

The code above uses IO::Compress::Gzip, and takes the two files as arguments on the command line. The ratio in this case is computed by saying that 100% would be if the content of the two files compressed to be the same size as one of them, 0% as compressing to the sum of the sizes of the two files.

(By the way, for the example files from my earlier post, this gave a result of 90.61%, which is a fair approximation.)

Update: 2007-09-24
Added comments to code; had reversed description of ratio.

In reply to Re^2: Module for Approximate File Comparison by atcroft
in thread Module for Approximate File Comparison by neversaint

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