shell脚本编程：if-then,case结构化命令

使用if-then语句

格式如下

if commands
then
    commands
fi
或
if commands; then
command
fi

举个栗子

#!/bin/bash
#testing a bad command
if asjfkd
then
    echo "it didn't work"
fi

再看个栗子

#!/bin/bash
#testing multiple commands in the then section
testuser=rich
if grep $testuser /etc/passwd
then
    echo the bash files for user $testuser are:
    ls -a /home/$testuser/.b*
fi

if-then-else语句

格式如下：

if commands
then 
    commands
else
    commands
fi

嵌套if语句

格式如下

if command1
then 
    commands
elif command2
then
    more commands
fi

case命令

先看case命令的格式，如下

case varialbe in
pattern1 | pattern2) command1;;
pattern3) command2;;
*) default commands;;
esac

看一个栗子

#！/bin/bash
case $USER in
rich | barbara)
    echo "welcome, $USER"
    echo "enjoy";;
testing)
    echo "special testing account";;
*)
    echo "sorry, you're not allowed here";;
esac