条件测试和结构化语句

[root@localhost ~]# [  -d /etc/vsftpd  ]

[root@localhost ~]# echo $?

0 //返回0表示条件成立

[root@localhost ~]# [  -d /etc/hosts  ]

[root@localhost ~]# echo $?

1 //返回1表示条件不成立

[root@localhost ~]# [ -e /media/cdrom ] && echo "YES"

YES //逻辑与，“而且”的意思

[root@localhost ~]# who | wc -l

7

[root@localhost ~]# [ $(who | wc -l) -gt 5 ] && echo "Too many." // 用户数是否 > 5

Too many. 

[root@localhost ~]# [ $(who | wc -l) -ge 10 ] && echo "> = 10."          //用户数是否 >= 10

[root@localhost ~]# FreeCC=$(free -m | grep Mem: | tr -s ‘ ’ |cut -d‘ ’ -f4）

[root@localhost ~]# [ $FreeCC -lt 1024 ] && echo ${FreeCC}MB        //空闲内存是否 < 1024MB

864MB

[root@localhost ~]# (( 10+2 > 10-2 )) && echo ok || echo no

ok

[root@localhost ~]# a=10

[root@localhost ~]# ((a>20)) && echo ok || echo no     //变量加不加$都可以

no

[root@localhost ~]# ((a<20)) && echo ok || echo no 

ok

[root@localhost ~]# ((a==20)) && echo ok || echo no     //注意这里是两个=，一个=是赋值

no

[root@localhost ~]# ((a!=20)) && echo ok || echo no    ///不等于只能用一个=

ok

[root@localhost ~]# echo $LANG   

zh_CN.UTF-8

[root@localhost ~]# [ $LANG !=  "en.US" ] && echo  "Not en.US"     //测试当前语言环境

Not en.US

[root@localhost ~]# read -p “是否覆盖现有文件（yes/no）？"  ACK

是否覆盖现有文件（yes/no）？yes

[root@localhost ~]# [ $ACK = "yes" ] && echo "覆盖"       //测试读入的字符串是否为 yes

覆盖

[root@localhost ~]# a=123

[root@localhost ~]# [ -z $a ] && echo ok || echo no

no

[root@localhost ~]# a=

[root@localhost ~]# [ -z $a ] && echo ok || echo no

ok

[root@localhost ~]# [ -n $a ] && echo ok || echo no                 

ok

[root@localhost ~]# [ -n "$a" ] && echo ok || echo no                    //和预计结果不一致

no

[root@localhost ~]# a="abc 123"

[root@localhost ~]# [ -z $a ] && echo ok || echo no

-bash: [: abc: binary operator expected                              //语法错误

no

[root@localhost ~]# [ -z "$a" ] && echo ok || echo no

no

[root@localhost ~]# [ "$a" = "abc 123" ] && echo ok || echo no

ok

[root@localhost ~]# a="abc 123"

[root@localhost ~]# [ $a = "abc 123" ] && echo ok || echo no  

-bash: [: too many arguments

no

[root@localhost ~]# [[ $a = "abc 123" ]] && echo ok || echo no

ok

[root@localhost ~]# cat test.sh

#!/bin/bash

[[ $1 = ??? ]] && echo ok || echo no   //匹配字符是任意三个字符的

[root@localhost ~]# ./test.sh ab

no

[root@localhost ~]# ./test.sh abc

ok

[root@localhost ~]# cat test.sh

#!/bin/bash

[[ $1 = a* ]] && echo ok || echo no    //匹配字符是a开头的

[root@localhost ~]# ./test.sh bbba

no

[root@localhost ~]# ./test.sh abb

ok

[root@localhost ~]# cat test.sh

read -s -p "please input password: " pass

[[ $pass = ???* ]] && echo passwd is ok || echo passwd too short

//判断密码的长度至少要3位

[root@localhost ~]# [ -d /etc/passwd -a -f /etc/fstab ] && echo ok || echo no

no

[root@localhost ~]# [ -d /etc/passwd -o -f /etc/fstab ] && echo ok || echo no 

ok

[root@localhost ~]# [ ! -d /etc/passwd ] && echo ok || echo no                  

ok

[root@localhost ~]# (( ! 10 > 5 )) && echo ok || echo no

no

[root@localhost ~]# cat test.sh

#!/bin/bash

If ! service httpd status &> /dev/null

then

           service httpd start

fi

[root@localhost ~]# cat pinghost.sh

#!/bin/bash

if ping -c 3 -i 0.2 -w 2 $1 &> /dev/null

then

 echo "Host $1 is up."

else

 echo "Host $1 is down."

fi

[root@localhost ~]# ./pinghost.sh 192.168.4.11

Host 192.168.4.11 is up.

[root@localhost ~]# ./pinghost.sh 192.168.4.13

Host 192.168.4.13 is down.

#!/bin/bash

if rpm -q sysstat &> /dev/null

then

 echo "已安装 `rpm -q sysstat`"

else

 echo "未安装，尝试自动安装"

    RHEL_DIR="/media/cdrom/Server/"

 if [ -d $RHEL_DIR ]

 then

 cd $RHEL_DIR

        rpm -ivh sysstat-*.rpm && echo "安装完成。"

 else

 echo "错误：无法访问光盘目录：$RHEL_DIR"

 fi

fi

#[root@localhost ~]# cat gradediv.sh   判断分数所在区间，给出不同的分档结果

#!/bin/bash

read -p "请输入您的分数（0-100）：" GRADE

if (( $GRADE >= 85 )) && (( $GRADE <= 100 ))

then

 echo "$GRADE 分！优秀"

elif (( $GRADE >= 70 )) && (( $GRADE <= 84 ))

then

 echo "$GRADE 分，合格"

else

 echo "$GRADE 分？不合格”

fi

[root@localhost ~]# ./gradediv.sh

请输入您的分数（0-100）：89

89 分！优秀

#!/bin/bash

name=sxkj

if [[ $1 = $name ]]

 then

 echo "不能创建$name这个用户"

 exit 1

 else

 useradd $1 && echo 123 | passwd --stdin $1 &> /dev/null

fi

echo "用户$1已经创造完成"

#!/bin/bash

j=$1

for ((i=1; i<=j; i++))

do

 touch file$i && echo file $i is ok

done

#!/bin/bash

for i in $(arp | tail -n +2 | tr -s ‘ ‘ | cut -d‘ ‘ -f1)

do

   arp -d $i

done

[root@localhost ~]# for i in {0..9}; do echo $RANDOM;done

[root@localhost ~]# for i in $( seq 10); do echo $RANDOM;done

#!/bin/bash

echo "准备倒数5秒"

for i in $(seq 5 -1 1)

do

 echo -en "$i“

 sleep 1

done

echo -e "开始"

#!/bin/bash

echo "准备倒数5秒"

for i in $(seq 5 -1 1)

do

 echo -en "$i\b"

 sleep 1

done

echo "开始"

[root@localhost ~]# cat uaddfor.sh

#!/bin/bash

ULIST=$(cat /root/users.txt)

for UNAME in $ULIST

do

 useradd $UNAME

 echo "123456" | passwd --stdin $UNAME

done

[root@localhost ~]# ./uaddfor.sh

[root@localhost ~]# tail -3 /etc/passwd

chenye:x:1011:1011::/home/chenye:/bin/bash

dengchao:x:1012:1012::/home/dengchao:/bin/bash

zhangjie:x:1013:1013::/home/zhangjie:/bin/bash

#!/bin/bash

for i in $@ #可替换成for i

do

 useradd $i && echo user $i is ok

 echo 123456 | passwd --stdin $i &> /dev/null

done

[root@localhost ~]# ./myuseradd.sh aa bb cc dd

user aa is ok

user bb is ok

user cc is ok

user dd is ok

[root@localhost ~]# cat /root/ipadds.txt

192.168.4.11

192.168.4.110

192.168.4.120

[root@localhost ~]# cat chkhosts.sh

#!/bin/bash

HLIST=$(cat /root/ipadds.txt) #从列表文件读取IP地址

for IP in $HLIST

do

 ping -c 2 -i 0.2 -w 1 $IP &> /dev/null

 if (($?==0)) ; then

 echo "Host $IP is up."

 else

 echo "Host $IP is down." #嵌套if语句判断连通性

 fi

done

[root@localhost ~]# ./chkhosts.sh

Host 192.168.4.11 is up.

Host 192.168.4.110 is down.

Host 192.168.4.120 is up.

#!/bin/bash

for i in `seq 6`

do 

if ((i % 2 == 0 ))

then

 break;

fi

echo $i;

done

#!/bin/bash

for i in `seq 6`

do

if ((i % 2 == 0 ))

 then

 continue;

 fi

echo $i;

done

[root@localhost ~]# test.sh           

警告: vsftpd 服务没有启动，准备启动

为 vsftpd 启动 vsftpd：                                    [确定]

[root@localhost ~]# test.sh           

监听地址: 0.0.0.0:21

进程PID: 10478

[root@localhost ~]# yum remove vsftpd

[root@localhost ~]# test.sh

vsftpd服务不存在

[root@localhost test]# ./test.sh 78

成绩合格

[root@localhost test]# ./test.sh 93

成绩优秀

[root@localhost test]# ./test.sh 101

输入错误，请输入0-100间的整数

[root@localhost test]# ./test.sh 60

及格万岁

[root@localhost test]# ./test.sh 31

你需要补考

[root@localhost test]# bash lucky.sh

欢迎来到我是歌手第2季，还有3位参赛歌手，请按任意键开始选择

****这次为大家献唱的是谁呢？我们一起倒数3秒钟****

3 2 1 会是谁呢？

有请歌手‘丝丝‘登台

还有位2位歌手，下次又会是谁呢，O(∩_∩)O哈哈~

[root@localhost test3]# bash lucky.sh

欢迎来到我是歌手第2季，还有2位参赛歌手，请按任意键开始选择

****这次为大家献唱的是谁呢？我们一起倒数3秒钟****

3 2 1 会是谁呢？

有请歌手‘龙龙‘登台

只剩下1位压轴歌手啦，万众瞩目的一天就要来到了，(*^__^*) 嘻嘻……

[root@localhost test3]# bash lucky.sh

没得选了，就是有歌坛赵本山之称的‘安安‘啦,我是歌手下季将重新开始哦

[root@localhost ~]# ./test.sh 11 

脚本有1个参数

$1 is 11

[root@localhost ~]# ./test.sh aa bb

脚本有2个参数

$1 is aa

$2 is bb

[root@localhost ~]# ./test.sh aa bb cc

脚本有3个参数

$1 is aa

$2 is bb

$3 is cc

[root@localhost ~]# ./test.sh 

脚本没有接参数

[root@localhost ~]# ./test.sh

aa have 41 files

bb have 110 files

[root@localhost ~]# ./test.sh

all png files total size is 2540k

[root@servera ~]# bash add.sh

请输入用户名的前缀: stu

请输入用户的数目: 15

最多只能同时新建10个用户

[root@servera ~]# bash add.sh

请输入用户名的前缀: sxkj

请输入用户的数目: 2

用户sxkj1已经创建成功

用户sxkj2已经创建成功

一共创建的用户数:2个

[root@servera ~]# add.sh

请输入用户名的前缀: rr

请输入用户的数目: 2

用户rr1已经创建成功

用户rr2已经创建成功

一共创建的用户数:2个

[root@servera ~]# del.sh

请输入需要删除的用户名前缀:

请输入合法的用户名前缀

[root@servera ~]# del.sh

请输入需要删除的用户名前缀:

请输入合法的用户名前缀

[root@servera ~]# del.sh

请输入需要删除的用户名前缀: r

root是系统用户不能删除

rpc是系统用户不能删除

rtkit是系统用户不能删除

rpcuser是系统用户不能删除

用户rr1已经被成功删除

用户rr2已经被成功删除

一共删除的用户数:2个