Shell symbol interpretation (continuously updated)

Table of contents

One, $# 

Two, -ne

3. NR

Four, $$

 Five, lt

Six, $@

Seven, ${a[@]}   

8. ${#a[*]}

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One, $# 

$#: Indicates the number of parameters passed to the script.

$1: Indicates the first parameter passed to the script. $0 is the script itself

---

Two, -ne

-ne: Check whether two numbers are not equal, and return True if they are not equal

#! /bin/bash
num1=1
num2=2
if [ $num1 -ne $num2 ];then
   echo "$num1 和 $num2 不相等"
else
   echo "$num1 和 $num2 相等"
fi

---

3. NR

NR: is the total number of lines read

---

Four, $$

$$ will get the current process ID number of the script running

---

 Five, lt

-lt	Checks if the number on the left is less than the number on the right, and if so, returns true.

---

Six, $@

list of all parameters

Screenplay:

#!/bin/bash
echo "所有的参数列表：$@"

run: 

---

Seven, ${a[@]}   

Get all elements in the array 

---

8. ${#a[*]}

Get the number of arrays. a is the array name.

code:

 operation result: