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Shell Function
2022-07-02 01:04:00 【Hadron's blog】
One , Definition of function （ Two ways ）
1.
function Function name {
command
} // This is a standard way of writing
2.
Function name （）{ // Most commonly used because of the most concise
command
}
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After the function is defined, it will not execute automatically , You need to call , The advantage is that you can write a piece of function code as a function , If you need to call the definition directly, it doesn't matter even if there are syntax errors , If you don't call, you won't report an error. Of course, the ultimate purpose of writing functions is to call , In order to implement a function block
Two , Function return value :
return Represents the exit function and returns an exit value , You can use $? The variable displays the value
Usage principle :
1、 Take the return value as soon as the function ends , because $? Variable returns only the exit status code of the last command executed
2、 Exit status code must be 0~255, If the value exceeds the value, it will be the remainder 256
example
444 % 256
1） Function call
Directly define the code block of the function in the script and write the function name to complete the call
#!/bin/bash
function fun1 { // Defines a function called fun1
echo "this is a function!" // The function body is to print "this is a function!
}
fun1 // Writing the function name directly will run the code in the function body
[[email protected] myscripts]# . fun.sh
this is a function!
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Be careful ①： Function name must be unique , If you define a , Use the same name to define , The second will override the function of the first , There are results you don't want , So be careful not to duplicate your name here ！
#!/bin/bash
f1 (){
echo hello
}
f1 (){
echo world
}
f1
[[email protected] ~]# . f1.sh
world
Be careful ②： The function must be defined before calling ！
#!/bin/bash
f1 (){
echo hello
}
f3 (){
echo "$(f1) $(f2)"
}
f2 (){
echo world
}
f3
Be careful ③： You don't have to define the function at the beginning of the script , As long as it is defined before the call
In case of nested calls in other places , You can't write the value of a function directly , Avoid being unable to recognize , You can use a reverse apostrophe , It is equivalent to the result of calling the function
#!/bin/bash
f1 (){
echo hello
}
f2 (){
echo world
}
f3 (){
echo "`f1` `f2`" // If it's directly f1 and f2 Words , It won't print out hello world And it will be f1 f2
}
f3
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3、 ... and , Example
vim localrepo. sh
#!/bin/bash
function backuprepo {
cd /etc/yum.repo.d
mkdir repo.bak
mv * .repo repo.bak
mount /dev/sr0 /mnt > /dev/null
}
makelocalrepo() {
echo '[local]
name= local
baseurl=file: / , /mnt
enabled=1
gpgcheck=0' > local.repo
}
uselocal repo (){
yum clean all > /dev/null
yum makecache > /dev/null
yum install -y httpd > /dev/null
}
######main#######
backuprepo
makelocalrepo
uselocalrepo
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Four , Function arguments
1. Sum two numbers
#!/bin/bash
sum(){
read -p " Please enter the first number ：" NUM1
read -p " Please enter the second number ：" NUM2
echo " The two numbers you entered are ： $NUM1 and $NUM2 "
SUM=$(( NUM1+$NUM2))
echo “ The sum of two numbers is ： $SUM”
}
sum
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1. Function scope
stay Shell The execution of the function in the script does not open a new child Shell, But only in the currently defined Shell Effective in the environment . If Shell The variables in the script are not specially set , The default is valid throughout the script . When writing scripts , Sometimes you need to limit the value of a variable inside a function , You can use built-in commands local To achieve . Use of internal variables of functions , It can avoid the influence of variables with the same name inside and outside the function on the script results .
shell Variables in scripts are globally valid by default
local command ： Restrict variables to functions and use
[[email protected] ~]# vim myfun.sh
myfun ()
{
local i
i=8
echo $i
}
i=9
myfun
echo $i
In the above script myfun The function uses local Command to set variables i, Its function is to change the variable i Inside the function .myfun Variables are also defined outside the function i, Internal variables i And global variables i They don't influence each other . When the script executes, the function... Is called first myfun, Function internal variables i by 8, So the output is 8. After calling the function , To the variable i The assignment is 9, Then print external variables i, So I output 9
myfunc() {
a=8
echo $a
}
myfunc
echo $a
#!/bin/bash
myfunc() {
a=8
echo $a
myfunc
a=9
echo $a I
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2. The ginseng
Arguments to functions
1） The parameters of the function
Calculate the location variable $1 and $2 And
#!/bin/bash
add (){
let sum=$1+$2 // The position variable here is the position variable of the function , So write it after the calling function , If it is used when calling a script, then Can't succeed
echo $sum
}
add 4 5
2） Script parameters
#!/bin/bash
add (){
let sum=$1+$2
echo $sum
}
add $1 $2 // This is equivalent to calling the parameters of the script , Then pass the location variable of the script to the function for calculation
Pass the parameters to the positional parameters in the function through the script $1
#!/bin/bash
fun1(){
rm -rf $1
}
fun1 $1
Pass parameters directly when calling a function
#!/bin/bash fun1(){
rm -rf $1
}
fun1 /root/a.txt
How to pass and use multiple parameters in functions
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3. Recursion of a function
The function itself calls itself
List the files in the directory , The catalogue is shown in blue , The file displays hierarchical relationships
#!/bin/bash
list(){
for i in $1/*
do
if [ -d $i ];then
echo -e "\e[34m$i\e[0m"
list $i " $2"
else
echo "$2$i"
fi
done
}
list $1 $2
Calculation 5 The factorial
# Factorial 5！ 5*4*3*2*1
#!/bin/bash
fa () {
if [ $1 -eq 1 ]
then
echo 1
else
local tp=$[ $1 - 1]
local res=$(fa $tp)
echo $[ $1 * $res ]
fi
}
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5、 ... and , Local and global variables
Variables defined in the script or not declared as local variables in the function body are global variables , It means at present shell The environment recognizes
If you need this variable to be used only in the function, you can use... In the function local Keyword declaration , In this way, even if there is a variable with the same name outside the function, it doesn't matter , It does not affect the use in the function body
If it is to use source If you execute the script, you can see the difference
[[email protected] ~]# a=nihao
#!/bin/bash // Write a function , Print first a Value , Then change a Reprint the value of
f1 (){
echo $a
a=world
echo $a
}
f1
[[email protected] ~]# source f1.sh // use source Execute the script , Will find a The value of
nihao
world
[[email protected] ~]# echo $a
world
Use... In the body of a function local Defining variables a Value
#!/bin/bash
f1 (){
echo $a
local a=world
echo $a
}
f1
[[email protected] ~]# source f1.sh // Execute script discovery a The value of
world
world
#!/bin/bash
f1 (){
echo $a
local a=world
echo $a
}
f1
echo $a
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