Extracts rpms to similarly named directories, using only bash, grep, tail, cpio and a decompressor

extractrpm

#!/bin/bash
mkdir -p ${1%.rpm} || exit 1
RPMHDRLGTH=$(LANG=C grep -abom1 '.7zXZ\|]'$'\000\000''....'$'\377\377\377\377\377\377''\|BZh9\|'$'\037\213\b' "$1")
case "$RPMHDRLGTH" in
  *7zXZ) COMPRESSOR=xz ;;
  *]*)   COMPRESSOR=lzma ;;
  *BZh9) COMPRESSOR=bzip2 ;;
  *)     COMPRESSOR=gzip ;;
esac
tail -c+$[${RPMHDRLGTH%:*}+1] "$1" | $COMPRESSOR -d | ( cd ${1%*.rpm} ; cpio --quiet -imd )

Just some notes. This assumes GNU tools. Additionally it will not work with rpm5.org rpm's that use xar instead of cpio internally.