root@epsybox:/git# cat /usr/local/bin/extract_initramfs_cpio.sh
#!/bin/bash
zImage=$1
#========================================================
# find start of gziped kernel object in the zImage file:
#========================================================
pos=`grep -P -a -b -m 1 --only-matching $'\x1F\x8B\x08' $zImage | cut -f 1 -d :`

#========================================================================
# the cpio archive might be gzipped too, so two gunzips could be needed:
#========================================================================
if [ "$pos" = "" ]; then
        cp $zImage /tmp/kernel.img
else
        echo "-I- Extracting kernel image from $zImage (start = $pos)"
        dd if=$zImage bs=1 skip=$pos | gunzip > /tmp/kernel.img
fi
pos=`grep -P -a -b -m 1 --only-matching $'\x1F\x8B\x08' /tmp/kernel.img | cut -f 1 -d :`
#===========================================================================
# find start and end of the "cpio" initramfs image inside the kernel object:
# ASCII cpio header starts with '070701'
# The end of the cpio archive is marked with an empty file named TRAILER!!!
#===========================================================================
if [ ! "$pos" = "" ]; then
   echo "-I- Extracting compressed cpio image from kernel image (start = $pos)"
   dd if=/tmp/kernel.img bs=1 skip=$pos | gunzip > /tmp/cpio.img
   start=`grep -a -b -m 1 --only-matching '070701' /tmp/cpio.img | head -1 | cut -f 1 -d :`
   end=`grep -a -b -m 1 --only-matching 'TRAILER!!!' /tmp/cpio.img | head -1 | cut -f 1 -d :`
   inputfile=/tmp/cpio.img
else
   echo "-I- Already uncompressed cpio.img, not decompressing"
   start=`grep -a -b -m 1 --only-matching '070701' /tmp/kernel.img | head -1 | cut -f 1 -d :`
   end=`grep -a -b -m 1 --only-matching 'TRAILER!!!' /tmp/kernel.img | head -1 | cut -f 1 -d :`
   inputfile=/tmp/kernel.img
fi

end=$((end + 10))
count=$((end - start))
if (($count < 0)); then
   echo "-E- Couldn't match start/end of the initramfs image."
   exit
fi
echo "-I- Extracting initramfs image from $inputfile (start = $start, end = $end)"
dd if=$inputfile bs=1 skip=$start count=$count > initramfs.cpio

#to unpack...  cpio