关于linux程序设计第二章CD数据库应用程序总结、

版权声明：吸猫大法、 https://blog.csdn.net/sasuke__/article/details/79496630

#!/bin/bash



menu_choice=""
current_cd=""
title_file="title.cdb"
tracks_file="tracks.cdb"
temp_file=/tmp/cdb.$$
trap 'rm -f $temp_file' EXIT

get_return() {
	echo -e "Press return \c"
	read x
	return 0
}

get_confirm() {
	echo -e "Are you sure? \c"
	while true
	do
		read x
		case "$x" in
		y | yes | Y | Yes | YES )
			return 0;;
		n | no | N | No | NO )
			echo 
			echo "Cancelled"
			return 1;;
		* ) echo "Please enter yes or no" ;;
		esac
	done
}

set_menu_choice() {
	clear
	echo "Option :-"
	echo 
	echo "	a) Add new CD"
	echo "	f) Find CD"
	echo "	c) Count the CDs and tracks in the catalog"
	if [ "$cdcatnum" != "" ]; then
		echo "	l) List tracks on $cdtitle"
		echo "	r) Remove $cdtitle"
		echo "	u) Update track information for $cdtitle"
	fi
	echo "	q) Quit"
	echo 
	echo -e "Please enter choice then press return \c"
	read menu_choice
	return 
}
insert_title() {
	echo $* >> $title_file
	return 
}

insert_track() {
	echo $* >> $tracks_file
	return 
}

add_record_tracks() {
	echo "Enter track information for this CD"
	echo "When no more tracks enter q"
	cdtrack=1
	cdttitle=""
	while [ "$cdttitle" != "q"]; do
		echo -e "Track $cdtrack. track title? \c"
		read tmp
		cdttitle=${tmp%%,*}
		if [ "$tmp" != "$cdttitle" ]; then
			echo "Sorry, no commas allowd"
			continue
		fi
		if [ -n "$cdttitle" ] ; then
			if [ "$cdttitle" != "q" ] ; then 
				insert_track $cdcatnum,$cdtrack,$cdttitle
			fi
		else
			cdtrack=$((cdtrack-1))
		fi
		cdtrack=$((cdtrack+1))
	done
}
add_records () {
	#prompt for the initial information

	echo -e "Enter catalog name \c"
	read tmp
	cdcatnum=${tmp%%,*}
	
	echo -e "Enter title \c"
	read tmp
	cdtitle=${tmp%%,*}

	echo -e "Enter type \c"
	read tmp
	cdtype=${tmp%%,*}

	echo -e "Enter artist/composor \c"
	read tmp
	cdac=${tmp%%,*}

	#Check that they want to enter the information
	echo About to add new enter
	echo "$cdcatnum,$cdtitle,$cdtype,$cdac"

	#if confirmed then append it to the titles file

	if get_confirm ; then
		insert_title $cdcatnum,$cdtitle,$cdtype,$cdac
		add_records_tracks
	else
		remove_records
	fi
}

find_cd () {
	if [ "$1" = "n"]; then
		asklist=n
	else
		asklist=y
	fi
	cdcatnum=""
	echo -e "Enter a string to search for in the cd title \c"
	read searchstr
	if [ "$searchstr" = "" ]; then
		return 0
	fi

	grep "$searchstr" $title_file > $temp_file

	set $(wc -l $temp_file)
	linesfound=$1
	
	case "$linesfound" in
	0 )	echo "Sorry, nothing found"
		get_return
		return 0;;
	1 )	;;
	2 )	echo "Sorry not unique."
		echo "Found the following"
		cat $temp_file
		get_return
		return 0
	esac
	IFS=","
	read cdcatnum cdtitle cdtype cdac < $temp_file
	IFS=" "
	if [ -z "$cdcatnum" ]; then
		echo "Sorry, could not extract catalog field from $temp_file"
		get_return
		return 0
	fi

	echo 
	echo Catalog number: $cdcatnum
	echo Title: $cdtitle
	echo Type: $cdtype
	echo Artist/Composor: $cdac
	echo 
	get_return
	if [ "$asklist" = "y" ]; then
		echo -e "View tracks for this CD? \c"
			read x
		if [ "$x" = "y"];	then
			echo 
			list_tracks
			echo 
		fi
	fi
	return 1
}

update_cd() {
	if [ -z "$cdcatnum" ]; then
		echo "You must select a CD first"
		find_cd n
	fi
	
	if [ -n "$cdcatnum" ]; then
		echo "Current tracks are :-"
		list_tracks
		echo 
		echo "This will re-enter the tracks for $cdtitle"
		get_confirm && {
			grep -v "^${cdcatnum}," $tracks_file > $temp_file
			mv $temp_file $tracks_file
			echo 
			add_records_tracks
		}
	fi
	return 
}
count_cds () {
	set $(wc -l $title_file)
	num_titles=$1
	set $(wc -l $tracks_file)
	num_tracks=$1
	echo found $num_titles cds, with a totoal of $num_tracks tracks
	get_return
	return
}

remove_records () {
	if [ -z "$cdcatnum" ]; then
		echo You must select a CD first
		find_cd n
	fi
	
	if [ -n "$cdcatnum" ]; then
		echo "You are about to delete $cdtitle"
		get_confirm && {
			grep -v "^${cdcatnum}," $title_file > $temp_file
			mv $temp_file $title_file
			grep -v "^${cdcatnum}," $tracks_file > $temp_file
			mv $temp_file $tracks_file
			cdcatnum=""
			echo Enter removed
		}
	get_return
	fi
	return
}

list_tracks () {
	if [ "$cdcatnum" = "" ]; then
		echo no CD selected yet
		return 
	else
		grep "^${cdcatnum}," $tracks_file > $temp_file
		num_tracks=$(wc -l $temp_file)
		if [ "$num_tracks" = "0" ]; then
			echo no tracks found for $cdtitle
		else {
			echo
			echo "$cdtitle :-"
			echo 
			cut -f 2- -d, $temp_file
			echo 
		} | ${PAGER:-more}
		fi
	fi
	get_return
	return
}

rm -f $temp_file
if [ ! -f $title_file ]; then
	touch $title_file
fi

if [ ! -f $tracks_file ]; then
	touch $tracks_file
fi

#Now the application proper

clear
echo 
echo 
echo "Mini CD manager"
sleep 1

quit=n
while [ "$quit" != "y" ]; do
	set_menu_choice
	case "$menu_choice" in
	a ) add_records;;
	r ) remove_records;;
	f ) find_cd y;;
	u ) update_cd;;
	c ) count_cds;;
	l ) list_tracks;;
	b )
		echo 
		more $title_file
		echo 
		get_return
		;;
	q | Q )	quit=y ;;
	* ) echo "Sorry, choice not recognized" ;;
	esac
done

#Tiny up and leave

rm -f $temp_file
echo "Finished"
exit 0

对于以上有些还有疑问的地方总结一下

1.trap 命令

参考：传送门

常用的信号

EXIT、INT、DEBUG、ERR

在上述例子中只是运用trap捕捉EXIT(正常退出)信号来删除临时文件

2.set 命令

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上述例子中的用法就是为shell重新设置环境变量

下面通过一个shell脚本来由现象看作用

#!/bin/bash

echo the date is $(date)

echo $*

set $(date)

echo the date is $2

for i in $*; do
	echo $i
done

exit 0

3.IFS

参考文章：传送门

大致的说的话就是域分隔符

通过下面的例子来验证

#!/bin/bash

read x y
echo $x $y
IFS=“,”
read x y
echo $x $y

暂时补充这么多

还有的部分还没彻底懂、