String cutting, expect interaction, regular expressions [the third day of shell]

String handling

Substring interception

1.${变量名：起始位置（从0开始）：长度}

[root@server0 ~]# phone=18676749523
[root@server0 ~]# echo $phone
18676749523
[root@server0 ~]# echo ${phone:0:5}
18676
[root@server0 ~]# echo ${phone:2:5}
67674
查看位数
[root@server0 ~]# echo ${#phone}
11

---

2.expr substr $变量名  起始位置  长度

[root@server0 ~]# expr substr $phone 1 5
18676
[root@server0 ~]# expr substr $phone 3 2
67

---

3.echo $变量名 | cut -b 起始位置-结束位置

杠号为2到4

[root@server0 ~]# echo $phone | cut -b 2-4
867

 逗号为取该位置

[root@server0 ~]# echo $phone | cut -b 2,5,8
869

An example of string interception:
[Use a random number to take one of the digits [script]]

例：
#!/bin/bash
i='abcdefghijklmnopqrstuvwxyz1234567890zxcvbnmasdfghjkl'
n=$[RANDOM%53+1]
echo $i | cut -b $n

n=$[RANDOM%53] does not add 1 because it starts from 0
echo ${i:$n:1}

---

在变量i的后面继续取值

例：
[root@server0 /]# i=1
[root@server0 /]# p=$p$i
[root@server0 /]# echo $p
1
[root@server0 /]# i=0
[root@server0 /]# p=$p$i
[root@server0 /]# echo $p
10

---

      替换
echo ${变量名/需替换的数字n/*} 替换第一个数字n为*
echo ${变量名//需替换的数字n/*} 替换所有的n为*

例：
[root@server0 /]# echo $phone
18676749525
[root@server0 /]# echo ${phone/8/}
1676749525
[root@server0 /]# echo ${phone/5/}
1867674925
[root@server0 /]# echo ${phone//5/}
186767492
[root@server0 /]# echo ${phone//495/}
186767*25
[root@server0 /]# echo ${phone//495/}
18676725

---

       匹配删除
 1.
echo ${变量名#*:}从开头一直删除到第一个：
echo ${变量名##*:}从开头删除到最后的：

例：
[root@server0 /]# n=head -1 /etc/passwd
[root@server0 /]# echo $n
root:x:0:0:root:/root:/bin/bash
[root@server0 /]# echo ${n#:}
x:0:0:root:/root:/bin/bash
[root@server0 /]# echo ${n##:}
/bin/bash

  2.
echo ${变量名%：*}从后开始删除到:
echo ${变量名%%：*}从后开始删除所有到：

例：
[root@server0 /]# echo ${n%:}
root:x:0:0:root:/root
[root@server0 /]# echo ${n%%:}
root

---

利用匹配删除批量修改文件名：

#!/bin/bash
for i in ls *.jpg[View files ending with jpg]
do
mv $i ./${i%.*}.doc [Change to ending with doc]
done

---

    判断变量并赋值   

echo ${variable1:-variable2} If variable 1 exists, display it, if not, display variable 2

例：
[root@server0 /]# echo ${who:-dc}
dc
[root@server0 /]# who=000
[root@server0 /]# echo ${who:-dc}
000

    利用判断是否输入，无输入则执行100

#!/bin/bash
num=0
read -p "shu ru :" o
o=${o:-100}
for i in seq $o
do
let num+=i
done
echo $num

---

                        EXPECT自动交互 

Simulate character operation

send email (non-interactive)

mail -s header root << EOF (end)
hehe
hehe
EOF

Use expect to automatically interactively create directories remotely

#!/bin/bash
expect << EOF
spawn ssh 192.168.4.10
expect "password" {send "123456\n"}
expect "#" {send "mkdir /xxx.x\n"}
expect "#" {send "exit\n"}
EOF

Step
1) Install expect software
2) Write configuration file

#!/bin/bash
expect << EOF
1>spawn ssh 192.168.4.10 [command line]
2>expect "password" {send "123456\n"} [command line]
3>expect "#" {send "mkdir / xxx.x\n"} 【command line】
4>expect "#" {send "exit\n"} 【last line not executed】
EOF

1>Remote to the machine of ip192.168.4.10
2>When you see the word "passsword", enter 123456
3>When you see "#", create a directory
4>Do not execute, prevent the last command from being executed

Reasons for failure to run:
1. Is expect installed ? 2. Specify
a program that needs
interaction

ssh remote without confirmation
ssh -o StrictHostKeyChecking=no

---

                                               正则表达式

^ start
$ end
[] set, take any character in the set: grep [az] a.txt take any letter from a to z
[^] negate the set: [^abc] other than abc
. Any single character

• The previous character appears any number of times [not allowed to be used alone]
  . Any all == ( )
  {n,m} The previous character appears n to m times
  {n,} The previous character appears n or more times
  {n } The previous character appears n times

                         扩展正则表达式

  • Match at least once
    ? Match at most once
    {n,m} Match n to m times
    () Combine as a whole, preserving
    | or
    \b word boundaries

    Find the line containing the word init
    egrep '\binit\b' /etc/rc.local