Default [Q] Error when unpack boot.img-ramdisk.gz

Hi guys,

I do step by step from this thread

for unpack boot.img

step command

sudo cp mkbootimg /bin/
sudo chmod 755 /bin/mkbootimg
perl boot.img
mkdir ramdisk
cd ramdisk
gzip -dc ../boot.img-ramdisk.gz | cpio -I

when I use the last command it's show error message
cpio: premature end of archive

what's wrong?
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Mobile :LG G2
Tablet : Nexus 7 2013 LTE
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