Shell script function application

Records : 429

Scenario : Shell script function application, function definition, function call, function parameter passing.

Version : CentOS Linux release 7.9.2009.

1. Ordinary functions

The example ordinary function has no input parameters and no return value.

1.1 Script

Screenplay name: b2023051701.sh

Script content:

#!/bin/bash

#1.定义函数-带function关键字
function f1(){
    for city in "Hangzhou" "Suzhou" "Shanghai"
    do 
        echo "城市名称: ${city}"
    done
}

#2.定义函数-不带function关键字
f2(){
    for province in 'Zhejiang' 'Jiangsu'
    do 
        echo "省名称: ${province}"
    done
}

#3.调用函数
echo "f1输出结果:"
result=$(f1)
echo "${result}"
echo "f2输出结果:"
result=$(f2)
echo "${result}"

1.2 Execution and output

Execute the command: bash b2023051701.sh

Output result:

f1输出结果:
城市名称: Hangzhou
城市名称: Suzhou
城市名称: Shanghai
f2输出结果:
省名称: Zhejiang
省名称: Jiangsu

2. The function uses return to return the value

The return value of the Shell function can only be an integer between 0 and 255, and only 0 indicates success, and other values indicate failure.

When using the Shell function, the actual meaning of using return to return the value is not very obvious.

2.1 Script

Screenplay name: b2023051702.sh

Script content:

#!/bin/bash

#1.定义函数,使用return返回值
function f1(){
    echo '计算两数相乘结果'
    echo '输入第一个数字:'
    read firstNum
    echo '输入第二个数字:'
    read secondNum
    return $((${firstNum}*${secondNum}))
}

#2.调用函数f1
f1
echo "f1计算结果: $? "

2.2 Execution and output

Execute the command: bash b2023051702.sh

Output result:

计算两数相乘结果
输入第一个数字:
33
输入第二个数字:
3
f1计算结果: 99

3. The function uses the echo output as the return value

The function uses the echo output as the return value.

3.1 Script

Screenplay name: b2023051703.sh

Script content:

#!/bin/bash

#1.定义函数,使用echo输出作为返回值
function f2(){
  firstNum=1024
  secondNum=3
  echo $((firstNum*secondNum))
}

#2.调用函数f2
result=$(f2)
echo "f2计算结果:"
echo "${result}"

3.2 Execution and output

Execute command: bash b2023051703.sh

Output result:

f2计算结果:
3072

4. Functions use global variables as return values

Functions use global variables as return values.

4.1 Script

Screenplay name: b2023051704.sh

Script content:

#!/bin/bash

#1.定义函数,使用全局变量作为函数返回值
result=0 #全局变量存放函数结果
function f3(){
  firstNum=1024
  secondNum=4
  result=$((firstNum*secondNum))
}

#2.调用函数f3
f3
echo "f3计算结果:"
echo "${result}"

4.2 Execution and output

Execute the command: bash b2023051704.sh

Output result:

f3计算结果:
4096

5. Function passing parameters

Functions pass parameters using placeholders.

5.1 Script

Screenplay name: b2023051705.sh

Script content:

#!/bin/bash

# 1.定义函数,使用占位符定义参数
function f1(){
   echo "country: $1"
   echo "Province: $2"
   echo "City: $3"
}

#2.调用函数,传递参数
result=$(f1 "China" "Zhejiang" "Hangzhou")
echo "执行结果: "
echo "${result}"

5.2 Execution and output

Execute the command: bash b2023051705.sh

Output result:

执行结果: 
country: China
Province: Zhejiang
City: Hangzhou

6. The function uses return to return the value

Functions pass parameters using placeholders. Input parameters from the script execution entry.

6.1 Script

Screenplay name: b2023051706.sh

Script content:

#!/bin/bash

# 1.定义函数,使用占位符定义参数
function f1(){
   echo "country: $1"
   echo "Province: $2"
   echo "City: $3"
}

#2.调用函数,传递参数
v1=$1
v2=$2
v3=$3
result=$(f1 ${v1} ${v2} ${v3})
echo "执行结果: "
echo "${result}"

6.2 Execution and output

Execution command: bash b2023051706.sh Hangzhou, Zhejiang, China

Output result:

执行结果: 
country: 中国
Province: 浙江
City: 杭州

Above, thanks.

May 17, 2023

Shell script function application

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