which

UNIX下SH的实现源码

#
# which - emulation of `which' as it appears in FreeBSD
#
# usage: which [-as] command [command...]
#

which()
{
	local aflag sflag ES a opt

	OPTIND=1
	while builtin getopts as opt ; do
		case "$opt" in
		a)	aflag=-a ;;
		s)	sflag=1 ;;
		?)	echo "which: usage: which [-as] command [command ...]" >&2
			exit 2 ;;
		esac
	done

	(( $OPTIND > 1 )) && shift $(( $OPTIND - 1 ))

	# without command arguments, exit with status 1
	ES=1

	# exit status is 0 if all commands are found, 1 if any are not found
	for command; do
		# if $command is a function, make sure we add -a so type
		# will look in $PATH after finding the function
		a=$aflag
		case "$(builtin type -t $command)" in
		"function")	a=-a;;
		esac

		if [ -n "$sflag" ]; then
			builtin type -p $a $command >/dev/null 2>&1
		else
			builtin type -p $a $command
		fi
		ES=$?
	done

	return $ES
}