shell脚本编程<二>：if-then,case结构化命令

使用if-then语句

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

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

#!/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

if commands
then
commands
else
commands
fi

嵌套if语句

if command1
then
commands
elif command2
then
more commands
fi

case命令

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

#！/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