#! /bin/bash## cdhist - cd replacement with a directory stack like pushd/popd## usage: cd [-l] [-n] [-] [dir]## options:#	-l	print the cd directory stack, one entry per line#	-	equivalent to $OLDPWD#	-n	cd to nth directory in cd directory stack#	-s	cd to first directory in stack matching (substring) `s'## arguments:#	dir	cd to dir and push dir onto the cd directory stack## If the new directory is a directory in the stack and the options selected# it (-n, -s), the new working directory is printed## If the variable CDHISTFILE is set, the cd directory stack is loaded from# and written to $CDHISTFILE every time `cd' is executed.## Note: I got this off the net somewhere; I don't know the original author## Chet Ramey# chet@po.cwru.edu	_cd_print(){	echo -e "$@"}cd(){	typeset -i cdlen i	typeset t		if [ $# -eq 0 ]	then		set -- $HOME	fi		if [ "$CDHISTFILE" ] && [ -r "$CDHISTFILE" ] # if directory history exists	then		typeset CDHIST		i=-1		while read -r t			# read directory history file		do			CDHIST[i=i+1]=$t		done <$CDHISTFILE	fi		if [ "${CDHIST[0]}" != "$PWD" ] && [ -n "$PWD" ]	then		_cdins				# insert $PWD into cd history	fi		cdlen=${#CDHIST[*]}			# number of elements in history		case "$@" in	-)					# cd to new dir		if [ "$OLDPWD" = "" ] && ((cdlen>1))		then			'_cdprint' ${CDHIST[1]}			builtin cd ${CDHIST[1]}			pwd		else			builtin cd "$@"			# pwd		fi		;;	-l)					# _cdprint directory list		((i=cdlen))		while (((i=i-1)>=0))		do			num=$i			'_cdprint' "$num ${CDHIST[i]}"		done		return		;;	-[0-9]|-[0-9][0-9])			# cd to dir in list		if (((i=${1#-})<cdlen))		then			'_cdprint' ${CDHIST[i]}			builtin cd ${CDHIST[i]}			pwd		else			builtin cd $@			# pwd		fi		;;	-*)					# cd to matched dir in list		t=${1#-}		i=1		while ((i<cdlen))		do			case ${CDHIST[i]} in			*$t*)				'_cdprint' ${CDHIST[i]}				builtin cd ${CDHIST[i]}				pwd				break				;;			esac			((i=i+1))		done		if ((i>=cdlen))		then			builtin cd $@			# pwd		fi		;;	*)					# cd to new dir		builtin cd $@		# pwd		;;	esac	_cdins					# insert $PWD into cd history		if [ "$CDHISTFILE" ]	then		cdlen=${#CDHIST[*]}		# number of elements in history		i=0		while ((i<cdlen))		do			echo ${CDHIST[i]}	# update directory history			((i=i+1))		done >$CDHISTFILE	fi}	_cdins()					# insert $PWD into cd history{						# meant to be called only by cd	typeset -i i	i=0	while (( i < ${#CDHIST[*]} ))		# see if dir is already in list	do		if [ "${CDHIST[$i]}" = "$PWD" ]		then			break		fi		((i=i+1))	done	if (( i>22 ))				# limit max size of list	then		i=22	fi	while (((i=i-1)>=0))			# bump old dirs in list	do		CDHIST[i+1]=${CDHIST[i]}	done	CDHIST[0]=$PWD				# insert new directory in list}	# examplesshopt -s expand_aliases# go to known place before doing anythingcd /echo CDHIST: "${CDHIST[@]}"for dir in /tmp /bin - -2 -ldo	cd $dir	echo CDHIST: "${CDHIST[@]}"	echo PWD: $PWDdoneexit 0