mycd，记录使用过的目录，便于跳转

有一大堆的目录要跳转，真的是记不过来，所以有了这片代码，记住使用过的目录，列出来，然后按数字顺序进入。

#!/bin/bash
# this piece of code is used to record the directories you want to shift often,
# and cd to them easily
# you need to add "alias mycd='. /the/path/of/this/script'"in .bashrc,
# or it does do nothing to the current shell

dirlogfile=/tmp/dirlogfile
declare -a linearray
linecount=0
maxrecord=5
currentpwd=`pwd`

#echo there $# variables
if [ $# -gt 1 ];then 
	cat << END
Usage: \$mycd /dir/name # current dir will be remebered
       \$mycd           # print last $maxrecord directories,and prompt to choose
END
fi

# if no argument,then print all history for choose
if [ $# -eq 0 ];then
	if [ -f $dirlogfile ];then
		historylines=`cat $dirlogfile | wc -l`
		if [ $historylines -eq 0 ];then
			echo No history
			return 1
		fi
		#only preserve $maxrecord in logfile
		if [ $historylines -gt $maxrecord ]; then
			tail -n $maxrecord $dirlogfile > $dirlogfile.tmp
			mv $dirlogfile.tmp $dirlogfile
		fi
	else
		touch $dirlogfile
		echo No history
		return 1
	fi
	# read logfile and print
	while read line; do
		linearray[$linecount]=$line
		# export the DIR varible to the current shell,so you can use them
		# in cp/rm commands
		export DIR$linecount=${linearray[$linecount]}
		echo $linecount ${linearray[$linecount]} DIR$linecount
		((linecount++))
	done < $dirlogfile

	echo "Please choose one directory:"
	read choose

	# press enter to do nothing
	if [ "$choose" == "" ];then
		echo No change
		return 0
	fi

	if [ "$choose" -ge "0" ] && [ "$choose" -lt "$linecount" ];then
		# if choose is effective,then save current path to history
		isinhistory=0
		if [ "currentpwd" != "${HOME}" ];then
			while read line; do
				if [ "$line" == "$currentpwd" ]; then
					isinhistory=1
					break
				fi
			done < $dirlogfile
			if [ $isinhistory -eq 0 ];then
				echo $currentpwd >> $dirlogfile
			else
				echo "Already in history"
			fi
		fi
		cd ${linearray[$choose]}
		return 0
	else
		echo unkown choose
		return 2
	fi
fi

if [ -d $1 ]; then
	isinhistory=0
	if [ ! -f $dirlogfile ];then
		touch $dirlogfile
	else
		while read line; do
			if [ "$line" == "$currentpwd" ]; then
				isinhistory=1
				break
			fi
		done < $dirlogfile
	fi
	if [ $isinhistory -eq 0 ] && [ "$currentpwd" != "${HOME}" ];then
		echo $currentpwd >> $dirlogfile
	else
		echo "Already in history"
	fi
	# you need to add "alias mycd='. /the/path/of/this/script'"in .bashrc
	cd $1
	return 0
else
	echo Error: $1 is not a direction
	return 3
fi