canary

#!/bin/sh
#
# Usage: canary COMMAND [ARGUMENTS...]
# Usage: canary SHELL_EVAL_EXPRESSION
#
# Silences the given command (both stdout and stderr) if its exit status
# is zero (a success) and then propagates that status back to the caller.
#
# Like a canary in a coal mine, this program exists to vocalize failures.
# It also prints the given command and its failing exit status to stderr.
#
# Written in 2014 by Suraj N. Kurapati <https://github.com/sunaku>

output=$(
  # capture stderr alongside stdout
  exec 2>&1

  # SHELL_EVAL_EXPRESSION was given
  test $# -eq 1 && set -- eval "$@"

  # execute the given command line
  "$@"
)
status=$?

if [ $status -ne 0 ]; then
  echo "canary: command exited with nonzero exit status $status" >&2
  echo "$output" # propagate output of failed command back to caller
fi

exit $status