Shell 四

14.shell脚本中的函数

函数就是把一段代码整理到了一个小单元中，并给这个小单元起一个名字，当用到这段代码时直接调用这个小单元的名字便可。

• 格式:

function f_name() 
{ 
        command
}

• 函数必需要放在最前面
• 示例1

#!/bin/bash
input() {
    echo $1 $2 $# $0
}

input 1 a b

[root@feature1 ~]# sh -x fun1.sh
+ input 1 a b
+ echo 1 a 3 fun1.sh
1 a 3 fun1.sh

• 示例2

#!/bin/bash
sum() {
    s=$[$1+$2]
    echo $s
}
sum 1 2

[root@feature1 ~]# vim fun2.sh
[root@feature1 ~]# sh -x fun2.sh
+ sum 1 2
+ s=3
+ echo 3
3

• 示例3

#!/bin/bash
ip() 
{
    ifconfig |grep -A1 "$1: " |tail -1 |awk '{print $2}'
}
read -p "Please input the eth name: " e
myip=`ip $e`
echo "$e address is $myip"

[root@feature1 ~]# sh -x fun3.sh
+ read -p 'Please input the eth name: ' e
Please input the eth name: enp0s3
++ ip enp0s3
++ grep -A1 'enp0s3: '
++ tail -1
++ awk '{print $2}'
++ ifconfig
+ myip=10.0.2.20
+ echo 'enp0s3 address is 10.0.2.20'
enp0s3 address is 10.0.2.20

[root@feature2 bin]# ifconfig |grep -A1 "enp0s3: "
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.200  netmask 255.255.255.0  broadcast 192.168.1.255
[root@feature2 bin]# ifconfig |grep -A1 "enp0s3: "|tail -l
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.200  netmask 255.255.255.0  broadcast 192.168.1.255
[root@feature2 bin]# ifconfig |grep -A1 "enp0s3: "| tail -l
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.200  netmask 255.255.255.0  broadcast 192.168.1.255
[root@feature2 bin]# ifconfig |grep -A1 "enp0s3: " | tail -1
        inet 192.168.1.200  netmask 255.255.255.0  broadcast 192.168.1.255

[root@feature2 bin]# ifconfig |grep -A1 "enp0s3: " | tail -1 |awk '{print $2}'
192.168.1.200

15.shell中的数组

• 定义数组 a=(1 2 3 4 5); echo ${a[@]}

[root@feature1 ~]# a=(1 2 3 4 5);
[root@feature1 ~]# echo ${a[@]}
1 2 3 4 5

• 获取数组的元素个数 echo ${#a[@]}

[root@feature1 ~]# echo ${#a[@]}
5

• 读取第三个元素，数组从0开始 echo ${a[2]}

[root@feature1 ~]# echo ${a[0]}
1
[root@feature1 ~]# echo ${a[1]}
2
[root@feature1 ~]# echo ${a[2]}
3

• 显示整个数组 echo ${a[*]} 等同于 ${a[@]}

[root@feature1 ~]# echo ${a[*]}
1 2 3 4 5
[root@feature1 ~]# echo ${a[@]}
1 2 3 4 5

• 数组赋值 a[1]=100; echo ${a[@]}

[root@feature1 ~]# a[1]=100;
[root@feature1 ~]# echo ${a[@]}
1 100 3 4 5
[root@feature1 ~]# a[5]=2; echo ${a[@]}
1 100 3 4 5 2
# 若是下标不存在则会自动添加一个元素

• 数组的删除 unset a; unset a[1]

[root@feature1 ~]# unset a;
[root@feature1 ~]# echo ${a[@]}

[root@feature1 ~]# a=(1 2 3 4 5);
[root@feature1 ~]# unset a[1]
[root@feature1 ~]# echo ${a[@]}
1 3 4 5

• 数组分片 a=(seq 1 5) 从第一个元素开始，截取3个 echo ${a[@]:0:3}

[root@feature1 ~]# a=(`seq 1 5`)
[root@feature1 ~]# echo ${a[@]:0:3}
1 2 3

从第二个元素开始，截取4个 echo ${a[@]:1:4}

[root@feature1 ~]# echo ${a[@]:1:4}
2 3 4 5

从倒数第3个元素开始，截取2个

echo ${a[@]:0-3:2}

[root@feature1 ~]# echo ${a[@]:0-3:2}
3 4

• 数组替换

echo ${a[@]/3/100}
a=(${a[@]/3/100})