whence

UNIX下SH的实现源码

#
# An almost-ksh compatible `whence' command.  This is as hairy as it is 
# because of the desire to exactly mimic ksh.
# 
# This depends somewhat on knowing the format of the output of the bash
# `builtin type' command.
#
# Chet Ramey
# [e-mail]
#
whence()
{
	local vflag= path=

	if [ "$#" = "0" ] ; then
		echo "whence: argument expected"
		return 1
	fi
	case "$1" in
		-v) vflag=1
		    shift 1
		    ;;
		-*) echo "whence: bad option: $1"
		    return 1
		    ;;
		 *) ;;
	esac

	if [ "$#" = "0" ] ; then
		echo "whence: bad argument count"
		return 1
	fi

	for cmd
	do
		if [ "$vflag" ]	 ; then
			echo $(builtin type $cmd | sed 1q)
		else
			path=$(builtin type -path $cmd)
			if [ "$path" ] ; then
				echo $path
			else
				case "$cmd" in
					/*) if [ -x "$cmd" ]; then
						echo "$cmd"
					    fi
					    ;;
					 *) case "$(builtin type -type $cmd)" in
						"") ;;
						 *) echo "$cmd"
						    ;;
					    esac
					    ;;
				esac
			fi
		fi
	done
	return 0
}