Shell编程入门(第二版)(中)

变量測试语句-test

作用：用来測试变量是否相等，是否为空，文件类型等。

格式：

test 測试条件 或 [] #范围：整数，字符串。文件

1）整数測试:

test int1 -eq int2 測试整数是否相等

test int1 -ge int2 測试int1是否>=int2

test int1 -gt int2 測试int1是否>int2

test int1 -le int2 測试int1是否<=int2

test int1 -lt int2 測试int1是否<int2

test int1 -ne int2 測试整数是否不相等

2）字符串測试:

test str1=str2 測试字符串是否相等

test str1!=str2 測试字符串是否不相等

test str1 測试字符串是否不为空

test -n str1 測试字符串是否不为空

test -z str1 測试字符串是否为空

3）文件測试:

test -d file 指定文件是否文件夹

test -f file 指定文件是否常规文件

test -x file 指定文件是否可运行

test -r file 指定文件是否可读

test -w file 指定文件是否可写

test -a file 指定文件是否存在

test -s file 文件的大小是否非0

注:test測试语句一般不单独使用,一般作为if语句的測试条件,如;

if test -d file
then
....
fi

test的变量的简写形式”[]”

演示样例-apachtest.sh

#!/bin/bash
# A test shell script for test Apache is running or not

web=$(/usr/bin/pgrep httpd)

echo "Now let's test the Apache..."
echo

#if [ "$web" != "" ]
if [ -n "$web" ]
then
echo "Apache is running..."
else
echo "Apache is NOT running..."
/etc/rc.d/init.d/httpd start
fi

流程控制语句

流控制语句:用于控制shell程序的流程

exit语句:退出程序运行,并返回一个返回码,返回码为0表示正常退出,非0表示非正常退出。

比如:exit 0

一、if

if/then格式

if test -d $1
then
...
fi

演示样例-if_then.sh

#!/bin/bash
# A test shell script for if/then

if [ -x /etc/rc.d/init.d/httpd ]
then
echo "Script: /etc/rc.d/init.d/httdp have x power!"
/etc/rc.d/init.d/httpd restart
fi

if/else格式

if 条件1
then
命令1
elif 条件2
then
命令2
else
命令3
fi

多个条件的联合:

-a: 逻辑与,仅当两个条件都成立时,结果为真。

-o: 逻辑或,两个条件仅仅要有一个成立,结果为真。

演示样例-if_else.sh

#!/bin/bash
# A test shell script for if/elif/else

echo -n "Please input a filename: "
read filename

if [ -d $filename ]
then
echo "$filename is a directory"
elif [ -f $filename ]
then
echo "$filename is a commen file"
elif [ -c $filename -o -b $filename ]
then
echo "$filename is a device file"
else
echo "$filename is a unkown file"
fi

演示样例-if_elif_exit.sh

#!/bin/bash
# A test shell script for if/elif

if [ $# -ne 2 ]
then
echo "Not enough parameters"
exit 1
fi

if [ $1 -gt $2 ]
then
echo "$1 is great then $2"
elif [ $1 -lt $2 ]
then
echo "$1 is little then $2"
else
echo "$1 is equal as $2"
fi

二、for/in

for 变量 in 名字表
do
命令列表
done

演示样例-for.sh

#!/bin/bash
# A test shell script for "for"

for DAY in Sunday Monday Tuesday Wednesday Thursday Friday Saturday
do
echo "The day is $DAY"
done

awk命令[分段提取]

awk -F域分隔符 ‘命令’[单引號] #假设不用-F指定切割符，默觉得空格

1、检測系统中UID为0的用户

awk -F: '$3==0 {print $1}' /etc/passwd

#awk -F: '{print $1}' /etc/passwd

-F： 指定切割附为：

$3 表示以：为切割附的第三位

2、检測系统中password为空的用户

awk -F: 'length($2)==0 {print $1}' /etc/shadow

#ps aux | grep -v root | awk '{print $2}'

演示样例-awk.sh

#!/bin/bash
# A test script for desplay users infomation

/bin/echo -n "Please input a username: "
read username

/bin/grep $username /etc/passwd > /dev/null 2> /dev/null

if [ $? -eq 0 ]
then
/bin/echo "username is: $username"
else
/bin/echo "user: $username is not exits."
exit 1
fi
/bin/echo

# list /etc/passwd info
userinfo=`/bin/grep ^$username:x /etc/passwd`
uid=`echo $userinfo | awk -F: '{print $3}'`
gid=`echo $userinfo | awk -F: '{print $4'}`
dir=`echo $userinfo | awk -F: '{print $6}'`
shell=`echo $userinfo | awk -F: '{print $7}'`

# get /etc/group info
groupinfo=`/bin/grep x:$gid /etc/group`
gname=`/bin/echo $groupinfo | awk -F: '{print $1}'`

/bin/echo "user id is: $uid"
/bin/echo "default group is: $gname"
/bin/echo "home directory is: $dir"
/bin/echo "shell is: $shell"
/bin/echo "group member info:"

# get group members
groups=`/usr/bin/groups $username`
/bin/echo $groups
/bin/echo

# get online info
online=`/usr/bin/who | grep $username`
if [ -z "$online" ]
then
echo "$username is not online"
else
echo "$username is online..."
fi

实例-killuser.sh

#思路:将一个用户全部的进程包含shell都关闭,则相当于将该用户踢出了系统
#!/bin/bash
# A shell sript to kill a user in Linux

username=$1

killpid=`/bin/ps aux | grep $username | awk '{print $2}'`

for PID in $killpid
do
/bin/kill -9 $PID 2> /dev/null
done