弱弱的问一个问题，关于cut,greb还有sed的

lw0203jojo

我是新学shell，有点地方不懂有人能教教我么？
要求是写一个程序用来存资料
比如存入user=jojo
但是当文件中已经有user=xxxx的时候报错：资料已存在
同时可以同过输入user来删除文件中user的行不存在时报错
基本的循环和case已经会写了
小弟不懂的就是如何取我输入的xxxx=yyyy中的xxxx来和文件资料匹配
还有我想用sed '/^xxxx/d' text来删除xxxx开头的那一行，显示是删除了，但是用cat查看的时候还在不知道为什么T.T
以下是原题（可以不用看，基本的不懂在上面说完了）
Write a shell script (to run on the Bourne shell) that allows a user to view, add, or delete a setting in a configuration file (config.txt) that contains settings in the form variable=value. The following is an example of such configuration file:

HOME=/u/soc/abc
HOST=lawson
HOSTTYPE=sun4
LOGNAME=abc
OSTYPE=solaris
PATH=/usr/dt/bin:/usr/openwin/bin:/bin:.
PS1=$
PS2=>
SHELL=/usr/bin/tcsh
TZ=Australia/Tasmania
USER=abc
VENDOR=sun
… … … …


Your script for this task must be named setting.sh. For ease of use, your script must present a menu of operations that a user may choose from. After the user makes a selection and that the selected operation has been completed, the menu must be displayed again so that the user can make another selection. For this assignment, validation check on user inputs is not essential (not considered in the marking).

Here is a sample output of your script. The $ is the shell prompt. The items in italics are not part of the sample output. They are hints indicating how your script should behave.

$ setting.sh

*** MENU ***
1. Add
2. Delete
3. View
Q - quit

CHOICE: 1 (user input)
Enter setting (format: ABCD=abcd): EDITOR=vi (user input)
New setting added
(sleep for 2 seconds to allow the user to see the output)

*** MENU ***
1. Add
2. Delete
3. View
Q - quit

CHOICE: 1 (user input)
Enter setting (format: ABCD=abcd): USER=jchen (user input)
Variable exists.
(sleep for 2 seconds)

*** MENU ***
1. Add
2. Delete
3. View
Q - quit

CHOICE: 3 (user input)
Enter variable name: EDITOR (user input)
EDITOR=vi
Requested setting displayed above.
(sleep for 2 seconds)

*** MENU ***
1. Add
2. Delete
3. View
Q - quit

CHOICE: 3 (user input)
Enter variable name: TIME (user input)
Variable does not exist.
(sleep for 2 seconds)

*** MENU ***
1. Add
2. Delete
3. View
Q - quit

CHOICE: 2 (user input)
Enter variable name: EDITOR1 (user input)
Variable does not exist.
(sleep for 2 seconds)

*** MENU ***
1. Add
2. Delete
3. View
Q – quit

CHOICE: 2 (user input)
Enter variable name: EDITOR (user input)
Setting deleted
(sleep for 2 seconds)

*** MENU ***
1. Add
2. Delete
3. View
Q – quit

CHOICE: 4 (user input)
Invalid choice.
(sleep for 2 seconds)

*** MENU ***
1. Add
2. Delete
3. View
Q - quit

CHOICE: q (user input)
(The running script is terminated. The shell prompt is displayed)