Linux Learning-Advanced shell scripting (a) function

Citation: Usually when you write a shell script, you'll find that there are many places that use the same code or the same functionality. If it's a small code, it doesn't matter. But if you use it more than once and it's the same code, I think you'll feel bored too. To be able to reuse the code, this uses the function.

Warm Tips
The format of the variable assignment is:

变量名=变量值

Precautions:

• The variable name should not precede the dollar "$" symbol. (different from php) equals "="
• There can be no spaces before and after. Unlike the C language, explicit syntax is not required in the shell to declare variables.
• The variable name cannot be directly connected to other characters, and if you want to connect it, you must use parentheses: echo "This is $ (he) llo!"

function Definition Format

function name {    commands}

or a

name() {}

This is a little bit like the other languages.

Example 1. no parameter function

A simple shell script that uses function functions
test1.sh

#!/bin/bash# this is a test file for test functionfunction func1 {        echo"this is an example of function!"}count=1echo"count‘s value is $count."while$count5 ]do        func1        $count1 ]doneecho"end of while."

Run:

sh test1.sh

Output:
Count ' s value is 1.
This is an example of function!
This is an example of function!
This is an example of function!
This is an example of function!
This is an example of function!
End of while.

Example 2. with parameter function

test2.sh

#!/bin/bash# This was a test file for test functionfunction Addem {if[$# -eq 0] || [$# -GT 2] Then                Echo-1        elif[$# -eq 1] Then                Echo$[ $+ $]Else                Echo$[ $+ $]fi}Echo-N"Adding and 5:"Value= ' AddemTen  the`Echo $valueEcho-N"Let's try adding just one number:"Value= ' AddemTen`Echo $valueEcho-N"Now trying adding no number:"Value= ' Addem 'Echo $valueEcho-N"Finally,we try adding three numbers:"Value= ' AddemTen  the  -`Echo $valueEcho "End of file."

Test:

sh test2.sh

Output:
Adding and 5:25
Let ' s try adding just one number:20
Now trying adding no number:-1
Finally,we try adding three numbers:-1
End of file.

If you want to declare a variable inside a function, you can define it by using local, which is represented as a local variable. such as local temp=1 .

Example 3. Array Parameters

test3.sh

#!/bin/bash  Span class= "hljs-comment" ># trying to pass a array variable  function testit {local newarray # use ' local ' define a local variable  newarray= (' echo  " the NewArray value is ${newarray[*]}  "}myarray= (1 , 2 , 3 , 4 , 5 ) echo   "the original array is:${ Myarray[*]}  " testit  $myarray   

Test:

sh test3.sh

Output:

The original array is:1,2,3,4,5
The NewArray value is 1,2,3,4,5

Example 4. function Recursion

Define the factorial function x! = x * (x-1)

function factorial {    if$1-eq1 ]    then        echo1    else        $11 ]        $temp`        echo $[$result$1]    fi}

Detailed Example: test4.py

#!/bin/bash# using recursionfunction factorial {        if$1-eq1 ]        then                echo1        else                $11 ]                $temp`                echo$result$1 ]        fi}

Test:

sh test4.py

Output:
Enter Value:6
The factorial of 6 is:720

Example 5. Using function commands on the command line

[root@master chapter16]# function multm {$[$1$2 ]> }[root@master chapter16]# multm 2 510

Note: When defining a function on the command line, if you give the function the same name as the built-in command or another command, the function overwrites the original command.

If you want to power on, you can unload the function into the/ETC/.BASHRC file.

Linux Learning-Advanced shell scripting (a) function