Shell script functions (function parameter transfer, recursion, library creation)

One, Shell function

• Write the sequence of commands together in a format
• Easy to reuse command sequence

1.Shell function definition

方法一：
function 函数名 {
    
    
命令序列
}

方法二：
函数名() {
    
    
命令序列
}

2. The return value of the function

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

Usage principles:
1. Take the return value as soon as the function ends, because the $? variable only returns the exit status code of the last command executed.
2. The exit status code must be 0~255, and the value will be divided by 256 if it exceeds

return

echo

Two, function parameter transfer

#!/bin/bash
sum() {
    
    
s=$[$1 + $2]
echo $s
}
read -p "请输入第一个参数：" first
read -p "请输入第二个参数：" second
sum $first $second

Three, the scope of function variables

• Functions in Shell scripts are only valid in the current Shell environment
• Variables in Shell scripts are globally effective by default
• Use the local command to limit the variable to the function
  
  

Four, recursion

1. Factorial

fact() {
    
    
if [ $1 -eq 1 ]
then
  echo 1
else
  local temp=$[$1 - 1]
  local result=$(fact $temp)
echo $[$1 * $result]
fi
}
  read -p "请输入：" n
  result=$(fact $n)
  echo $result

2. Recursive directory

#!/bin/bash
listdir () {
    
    
for i in $1/*
do
  if [ -d $i ]
  then
    echo "$2$i:"
    listdir $i " $2"
  else
    echo "$2$i"
  fi
done
}
read -p "请输出目录名：" dir
listdir $dir ""

Five, create a library