Shell编程入门(第二版)(下)

流程控制语句

三、select/in[较少用]格式：[python] view plaincopy select [变量] in [关键字]
do
command 1
... ...
command n
done
#select把关键字中的每一项做成类似表单,以交互的方式执行do和done之间的命令

示例-select.sh[python] view plaincopy#!/bin/bash
# Show select usage

echo "What's your favorate OS?"

select var in "Linux" "Windows" "UNIX" "Other"
do
break
done

echo "You have selected $var"



四、case/esac格式：[python] view plaincopycase 变量 in
字符串1)
命令列表1
;;
...
字符串n)
命令列表n
;;
esac

示例-case.sh[python] view plaincopy#!/bin/bash
# Show Usage for case/esac

echo "*********************************"
echo "Please select a oprator as below:"
echo "C ... copy"
echo "D ... delete"
echo "B ... backup"
echo "*********************************"

read op
case $op in
C)
echo "copy...."
;;
D)
echo "delete...."
;;
B)
echo "backup..."
;;
*)
echo "Unknow operator!"
exit 1
esac

示例-select.case[python] view plaincopy#!/bin/bash
# A test shell script for select and case

echo "a is 5, b is 3, please select your method"
a=5
b=3;

select var in "a+b" "a-b" "a*b" "a/b"
do
break
done

case $var in
"a+b")
echo "a+b="`expr $a + $b `
;;
"a-b")
echo "a-b="`expr $a - $b`
;;
"a*b")
echo "a*b="`expr $a \* $b`
;;
"a/b")
echo "a/b="`expr $a / $b`
;;
*)
echo "input error..."
exit 1
esac

实例-/etc/rc.d/init.d/httpd部分源代码[python] view plaincopy# See how we were called.
case "$1" in
start)
start
;;
stop)
stop
;;
status)
;;
restart)
stop
start
;;
condrestart|try-restart)
if status -p ${pidfile} $httpd >&/dev/null; then
stop
start
fi
;;
force-reload|reload)
reload
;;
graceful|help|configtest|fullstatus)
$apachectl $@
RETVAL=$?
;;
*)
echo $"Usage: $prog {start|stop|restart|condrestart|try-restart|force-reload|reload|status|fullstatus|graceful|help|configtest}"
RETVAL=2
esac



五、while格式：[python] view plaincopywhile 条件 #无限:while true
do
命令
done

示例-while.sh[python] view plaincopy#!/bin/bash
# A usage for while

num=1
while [ $num -le 10 ]
do
echo $(expr $num \* $num)
let num++
done

示例-useradd.sh[python] view plaincopy#!/bin/bash
# A shell script to add user(s)
#echo 123456 | passwd --stdin xiaofang #用非交互方式设置xiaofang的密码

echo -n "Plese input the user name: "
read username
echo -n "Plese input the sum users: "
read sum

num=1
while [ $num -le $sum ]
do
/usr/sbin/useradd "$username$num"
if [ $? -ne 0 ]
then
echo "user: $username already exists."
exit 1
fi

let num++
done

echo -n "Please input the passwd for this users: "
read passwd

i=1
while [ $i -le $sum ]
do
echo $passwd | /usr/bin/passwd --stdin "$username$i"
let i++
done



示例-userdel.sh[python] view plaincopy#!/bin/bash
# A shell script for delete user(s)

echo -n "Please input the username: "
read username
echo -n "Please input the user number: "
read num

i=1
while [ $i -le $num ]
do
/usr/sbin/userdel -r $username$i
if [ $? -ne 0 ]
then
echo "User: $username$i is not exists."
let i++
continue
fi

let i++
done

六、until格式:[python] view plaincopy until 条件
do
命令
done
#until类似while循环,不同的是until是条件返回值为假时才继续执行。

示例-until.sh[python] view plaincopy#!/bin/bash
# A script to show until usage.

echo "Please input Y/y to stop..."
read input

until [ "$input" = "Y" ] || [ "$input" = "y" ]
do
echo "input error, input again!"
read input
done

七、跳出循环:break和continue break:跳出整个循环 continue:跳过本次循环,进行下次循环 示例-break_continue.sh[python] view plaincopy#!/bin/bash
# A test shell script for break&continue

while true
do
echo "*****************************"
echo "Please have a select as blow:"
echo "1 Copy"
echo "2 Delete"
echo "3 Backup"
echo "4 Quit***********************"
read op

case $op in
"1")
echo "$op is Copy"
;;
"2")
echo "$op is Delete"
;;
"3")
echo "$op is Backup"
;;
"4")
echo "Exit..."
break
;;
"*")
echo "Invalide selectino, please select again..."
continue
;;
esac
done

八、shift指令 参数左移,每执行一次,参数序列顺次左移一个位置,$#的值减1, 用于分别处理每个参数,移出去的参数不再可用 示例-shift.sh[python] view plaincopy#!/bin/bash
# A test shell script for shift

if [ $# -lt 1 ]
then
echo "No enough parameters"
exit 1
fi

num=0
while [ $# -gt 0 ]
do
echo '$1 is '$1
let num++
shift
done

echo $num

函数应用

实例-/etc/rc.d/init.d/httpd中的start源代码

一、函数的定义: [python] view plaincopy函数名 ()
{
命令序列
}

二、函数的调用:不带() 函数名 参数1 参数2 ... 参数n实例-调用

三、函数中的变量: 变量均为全局变量,没有局部变量 四、函数中的参数: 调用函数时,可以传递参数,在函数中用$1、$2...来引用 示例-function.sh[python] view plaincopy#!/bin/bash
# A test shell script for function

# function
Help(){
echo "Usage: sh function \$1 \$2 \$3"
}

Display(){
echo "three argument: $1 $2 $3"
}

# main
if [ $# -ne 3 ]
then
Help
else
echo "Think you for your input"
Display $1 $2 $3
fi

Shell 脚本调试

sh -x script 这将执行该脚本并显示所有变量的值。 sh -n script 不执行脚本只是检查语法的模式,将返回所有语法错误。 最佳实践-命令最好使用绝对路径 一个脚本能够执行- 1.对脚本有rx权限,只有r,可以使用sh执行 2.对脚本所在目录至少有rx权限 拓展实例-setuid.sh[python] view plaincopy#!/bin/bash
# After the system installed, please check setuid files first for security
# mkdir /backup
# find / -perm -4000 -o -perm -2000 > /backup/setuid.list

/bin/find / -perm -4000 -o -perm -2000 > /tmp/setuid.list 2> /dev/null

for var in `/bin/cat /tmp/setuid.list`
do
/bin/grep $var /backup/setuid.list > /dev/null 2> /dev/null
if [ $? -ne 0 ]
then
echo "$var is not in /backup/setuid.list, It's danger!"
fi
done