Shell programming function (detailed introduction)

Shell programming function (detailed introduction)

One, the role of shell functions

Write the command sequence together in a format to facilitate repeated use of the command sequence

Second, the format of the shell function

1. Shell function definition

Format 1:

unction 函数名 {
    
    

 命令序列

}

Format 2:

函数名 （）{
    
    

 命令序列

}

2. Function return value

return means to exit the function and return an exit value, which can be displayed by the $? variable in the script

Principle of Use

• The return value is taken as soon as the function ends, because the $? variable only returns the exit status code of the last command executed
• The exit status code must be 0~255, and the value will be divided by 256 if it exceeds

Example:

Three, function parameter transfer

Example 1:

Example 2:

Fourth, the scope of function variables

Functions in shell scripts are only valid in the current shell environment

Variables in shell scripts are global by default

Use the local command to limit the variable to the function

Example 1:

#!/bin/bash
abc () {
    
    
   a=5
   b=6
   echo "c等于$c"
}

a=8
c=9
abc
echo "a等于$a"
echo "b等于$b"

Example 2:

#!/bin/bash
abc () {
    
    
   local i
   i=8
   echo "inside $i"
}

i=9
abc
echo "outside $i"

Example 3:

#!/bin/bash
abc () {
    
    
   echo "inside1 $i"
   let i++
   local i
   i=8
   echo "inside2: $i"
}

i=9
abc
echo "outside $i"
~       

Five, recursion

Function calls its own function

1. Factorial

1、[root@localhost ~]#vim 7.sh 

#!/bin/bash
fact () {
    
    
   if [ $1 -eq 1 ]
   then
       echo 1
   else
       local temp=$[$1 - 1]
       local result=$(fact $temp)
       echo "$[$1*$result]"
   fi
}

read -p "请输入阶乘数：" n
result=`fact $n`
echo "$result"

2、[root@localhost ~]#. 7.sh 
请输入阶乘数：5
120
[root@localhost ~]#

2. Recursive directory

#!/bin/bash
function list_files {
    
    
    for f in `ls $1`
    do
      if [ -d "$1/$f" ]
      then
          echo "$2$f"
          list_files "$1/$f" "$2"
      else
          echo "$2$f"
      fi
     done
}

list_files "/var/log" ""

Six, function library

1、[root@localhost ~]#vim 9.sh 

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

jianfa () {
    
    
   result=$[$1 - $2]
   echo $result
}

chengfa () {
    
    
   result=$[$1 * $2]
   echo $result
}
chufa () {
    
    
    if [ $2 -ne 0 ]
    then
        result=$[$1 / $2]
        echo $result
    else
      echo "$2不能等于0！"
    fi

2、[root@localhost ~]#vim 10.sh 

#!/bin/bash
. ~/9.sh

read -p "输入第一个参数值：" first
read -p "输入第二个参数值：" second

result1=`jiafa $first $second`
result2=`jianfa $first $second`
result3=$(chengfa $first $second)
result4=$(chufa $first $second)

echo $result1
echo $result2
echo $result3
echo $result4

3、[root@localhost ~]#vim 10.sh 
   [root@localhost ~]#. 10.sh 
   输入第一个参数值：10
   输入第二个参数值：30
   40
  -20
   300
   0