Applying Magento CE Patches

You must use bash, actually. On line 14 of the patch you explicitly pointed out is this code:

if (( $? != 0 )); then

$(( is a valid arithmetic expression in XCU sh, but (( is not.)

On many UNIX-like platforms, however, /bin/sh is just a symlink to /bin/bash. When invoked with the name sh, bash does disable some of its POSIXly-unstrict behavior, but not all of it. It's likely that these patches would work fine for bash invoked as sh.