xxd Shell

# Strip "0x" and ", " to get a plain hex string, then reverse it into bytes.
echo '0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x01, 0x00, 0x01, 0x00, 0x80, 0x00, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x21, 0xf9, 0x04, 0x01, 0x00, 0x00, 0x00, 0x00, 0x2c, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x02, 0x02, 0x44, 0x01, 0x00, 0x3b' | sed 's/0x//g; s/, //g' | xxd -r -p > pixel.gif