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rpm2cpio written in shell (i.e., tiny with no dependencies) https://trac.macports.org/attachment/ticket/33444/rpm2cpio
#!/bin/sh
pkg=$1
if [ "$pkg" = "" -o ! -e "$pkg" ]; then
echo "no package supplied" 1>&2
exit 1
fi
leadsize=96
o=`expr $leadsize + 8`
set `od -j $o -N 8 -t u1 $pkg`
il=`expr 256 \* \( 256 \* \( 256 \* $2 + $3 \) + $4 \) + $5`
dl=`expr 256 \* \( 256 \* \( 256 \* $6 + $7 \) + $8 \) + $9`
# echo "sig il: $il dl: $dl"
sigsize=`expr 8 + 16 \* $il + $dl`
o=`expr $o + $sigsize + \( 8 - \( $sigsize \% 8 \) \) \% 8 + 8`
set `od -j $o -N 8 -t u1 $pkg`
il=`expr 256 \* \( 256 \* \( 256 \* $2 + $3 \) + $4 \) + $5`
dl=`expr 256 \* \( 256 \* \( 256 \* $6 + $7 \) + $8 \) + $9`
# echo "hdr il: $il dl: $dl"
hdrsize=`expr 8 + 16 \* $il + $dl`
o=`expr $o + $hdrsize`
EXTRACTOR="dd if=$pkg ibs=$o skip=1"
COMPRESSION=`($EXTRACTOR |file -) 2>/dev/null`
if echo $COMPRESSION | grep -q gzip; then
DECOMPRESSOR=gunzip
elif echo $COMPRESSION | grep -q bzip2; then
DECOMPRESSOR=bunzip2
elif echo $COMPRESSION | grep -q xz; then
DECOMPRESSOR=unxz
elif echo $COMPRESSION | grep -q cpio; then
DECOMPRESSOR=cat
else
# Most versions of file don't support LZMA, therefore we assume
# anything not detected is LZMA
DECOMPRESSOR=`which unlzma 2>/dev/null`
case "$DECOMPRESSOR" in
/* )
;;
* )
DECOMPRESSOR=`which lzmash 2>/dev/null`
case "$DECOMPRESSOR" in
/* )
DECOMPRESSOR="lzmash -d -c"
;;
* )
DECOMPRESSOR=cat
;;
esac
;;
esac
fi
$EXTRACTOR 2>/dev/null | $DECOMPRESSOR
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