Re: RPMs :o(

Theodore Y. Ts'o (
Tue, 19 May 1998 23:50:46 -0400

Date: Tue, 19 May 1998 23:54:40 +0100 (BST)
From: Peter Horton <>

RPMs are basically gzipped cpio archives with a header.

If you search the file for the byte 0x1f followed by 0x8b (these bytes
mark a gzip file) and remove everything that precedes them, you will be
left a gzipped cpio archive, which you can then unzip and unpack.

Since this is so short, I'll take the liberty to repost the following
rpm2cpio perl script.

- Ted


# why does the world need another rpm2cpio? because the existing one
# won't build unless you have half a ton of things that aren't really
# required for it, since it uses the same library used to extract RPM's.
# in particular, it won't build on the HPsUX box i'm on.

# add a path if desired
$gzip = "gzip";

sub printhelp {
print "rpm2cpio, perl version by orabidoo <odar\>\n";
print "use: rpm2cpio [file.rpm]\n";
print "dumps the contents to stdout as a GNU cpio archive\n";
exit 0;

if ($#ARGV == -1) {
printhelp if -t STDIN;
$f = "STDIN";
} elsif ($#ARGV == 0) {
open(F, "< $ARGV[0]") or die "Can't read file $ARGV[0]\n";
$f = 'F';
} else {

printhelp if -t STDOUT;

# gobble the file up
undef $/;
$rpm = <$f>;
close ($f);

($magic, $major, $minor, $crap) = unpack("NCC C90", $rpm);

die "Not an RPM\n" if $magic != 0xedabeedb;
die "Not a version 3 RPM\n" if $major != 3;

$rpm = substr($rpm, 96);

while ($rpm ne '') {
$rpm =~ s/^\c@*//s;
($magic, $crap, $sections, $bytes) = unpack("N4", $rpm);
$smagic = unpack("n", $rpm);
last if $smagic eq 0x1f8b;
die "Error: header not recognized\n" if $magic != 0x8eade801;
$rpm = substr($rpm, 16*(1+$sections) + $bytes);

die "bogus RPM\n" if $rpm eq '';

open(ZCAT, "|gzip -cd") || die "can't pipe to gzip\n";
print STDERR "CPIO archive found!\n";

print ZCAT $rpm;
close ZCAT;

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