#! /bin/sh -

# some setup code
# ...

# run command passed as arguments:
"$@"; ret=$?

# some cleanup code

if [ "$ret" -gt 128 ] # only way to tell the command may have been killed
                      # with the current API
then
  sig=$(kill -l "$ret")

  trap : "$sig"   # in case the shell is zsh

  trap - "$sig"   # restore default disposition, unfortunately doesn't work
                  # if the signal was ignored on start with POSIX
                  # compliant shells. In zsh, can be worked around by setting
                  # a handler first, hence the previous line.

  kill -s "$sig" "$$" # report the same death by signal to caller if possible
fi
exit "$ret" # also fallback if kill failed to kill us above

The result of the logical negation operator ! is 0 if the value of its operand compares unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. The expression !E is equivalent to (0==E).

$ echo a b | xargs -n1 csh -c 'echo $1:q; false'
a
xargs: Command could not continue processing data

$ echo a b | xargs -n1 csh -c 'echo $1:q; false'
a
b

false() { return 1; }