autoload

linux下bash的源码

#
# An almost ksh-compatible `autoload'.  A function declared as `autoload' will
# be read in from a file the same name as the function found by searching the
# $FPATH (which works the same as $PATH), then that definition will be run.
#
# To do this without source support, we define a dummy function that, when
# executed, will load the file (thereby re-defining the function), then 
# execute that newly-redefined function with the original arguments.
#
# It's not identical to ksh because ksh apparently does lazy evaluation
# and looks for the file to load from only when the function is referenced.
# This one requires that the file exist when the function is declared as
# `autoload'.
#
# usage: autoload func [func...]
#
# The first cut of this was by Bill Trost, [e-mail]
#
# Chet Ramey
# [e-mail]

#
# Declare a function ($1) to be autoloaded from a file ($2) when it is first
# called.  This defines a `temporary' function that will `.' the file 
# containg the real function definition, then execute that new definition with
# the arguments given to this `fake' function.  The autoload function defined
# by the file and the file itself *must* be named identically.
#

aload()
{
	eval $1 '() {  . '$2' ; '$1' "$@" ; return $?; }'
}

#
# Search $FPATH for a file the same name as the function given as $1, and
# autoload the function from that file.  There is no default $FPATH.
#

autoload()
{
	#
	# Save the list of functions; we're going to blow away the arguments
	# in a second.  If any of the names contain white space, TFB.
	#

	local args="$*"

	#
	# This should, I think, list the functions marked as autoload and not
	# yet defined, but we don't have enough information to do that here.
	#
	if [ $# -eq 0 ] ; then
		echo "usage: autoload function [function...]"
		return 1
	fi

	#
	# If there is no $FPATH, there is no work to be done
	#

	if [ -z "$FPATH" ] ; then
		echo autoload: FPATH not set
		return 1
	fi

	#
	# This treats FPATH exactly like PATH: a null field anywhere in the
	# FPATH is treated the same as the current directory.
	#
	# The path splitting command is taken from Kernighan and Pike
	#

	fp=$(echo $FPATH | sed 's/^:/.:/
				s/::/:.:/g
				s/:$/:./
				s/:/ /g')

	for FUNC in $args ; do
		#
		# We're blowing away the arguments to autoload here...
		# We have to; there are no arrays.
		#
		set $fp

		while [ $# -ne 0 ] ; do
			if [ -f $1/$FUNC ] ; then
				break			# found it! 
			fi
			shift
		done

		if [ $# -eq 0 ] ; then
			echo "$FUNC: autoload function not found"
			continue
		fi

#		echo auto-loading $FUNC from $1/$FUNC
		aload $FUNC $1/$FUNC
	done

	return 0
}