Bzip2 mini-HOWTO

10. Using bzip2 to recompress other compression formats

The following perl program takes files compressed in other formats (.tar.gz, .tgz. .tar.Z, and .Z for this iteration) and repacks them for better compression. The perl source has all kinds of neat documentation on what it does and how it does what it does. This latest version takes files as input on the command line. Without command line arguments, it tries to repack every file in the current working directory.

#!/usr/bin/perl -w

#######################################################
#                                                     #
# This program takes compressed and gzipped programs  #
# in the current directory and turns them into bzip2  #
# format.  It handles the .tgz extension in a         #
# reasonable way, producing a .tar.bz2 file.          #
#                                                     #
#######################################################
$counter = 0;
$saved_bytes = 0;
$totals_file = '/tmp/machine_bzip2_total';
$machine_bzip2_total = 0;

 at raw = (defined  at ARGV)? at ARGV:<*>;

foreach( at raw) {
    next if /^bzip/;
    next unless /\.(tgz|gz|Z)$/;
    push  at files, $_;
}
$total = scalar( at files);

foreach ( at files) {
    if (/tgz$/) {
        ($new=$_) =~ s/tgz$/tar.bz2/;
    } else {
        ($new=$_) =~ s/\.g?z$/.bz2/i;
    }
    $orig_size = (stat $_)[7];
    ++$counter;
    print "Repacking $_ ($counter/$total)...\n";
    if ((system "gzip -cd $_ |bzip2 >$new") == 0) {
        $new_size = (stat $new)[7];
        $factor = int(100*$new_size/$orig_size+.5);
        $saved_bytes += $orig_size-$new_size;
        print "$new is about $factor% of the size of $_. :",($factor<100)?')':'(',"\n";
        unlink $_;
    } else {
        print "Arrgghh!  Something happened to $_: $!\n";
    }
}
print "You've "
    , ($saved_bytes>=0)?"saved ":"lost "
    , abs($saved_bytes)
    , " bytes of storage space :"
    , ($saved_bytes>=0)?")":"("
    , "\n"
    ;

unless (-e '/tmp/machine_bzip2_total') {
    system ('echo "0" >/tmp/machine_bzip2_total');
    system ('chmod', '0666', '/tmp/machine_bzip2_total');
}


chomp($machine_bzip2_total = `cat $totals_file`);
open TOTAL, ">$totals_file"
     or die "Can't open system-wide total: $!";
$machine_bzip2_total += $saved_bytes;
print TOTAL $machine_bzip2_total;
close TOTAL;

print "That's a machine-wide total of ",`cat $totals_file`," bytes saved.\n";