Comparison of if judgments of the shell

The IF function in the shell is beyond doubt that every 80% of the shells will be applied to if judgment, then as a novice I should be the whole, I heard a morning class today, and then the morning's things summed up a script, and then to the people to talk about

#!/bin/bash
##############################################################
# File Name:bbjj.sh
# version:v1.0
# Author:ls
# organization:http://shuai12138.blog.51cto.com/
# Created time:2017-03-06 14:04:05
# Description:
##############################################################
Read-p "Pleace input:"-T 2-n 1 x
echo ""
Read-p "Pleace input:"-t 2-n 1 y
echo "" >/dev/null
If [-N $x-N $y]
Then
if [["$x $y" =~ ^[0-9]+$]
Then
If [$x-gt $y]
Then
echo "$x > $y"
elif [$x-eq $y]
Then
echo "$x = $y"
Else
echo "$x < $y"
Fi
Else
echo "You must input number"
Fi
Else
echo "Error:you must input"
Fi

First, the first line of instructions: read-p "Pleace input:"-T 2-n 1 x

Read-p to script Interactive input "Pleace input" is the prompt message when executing the shell. The-T 2 means that after 2 seconds you do not type, then you exit. -N 1 means that I only restrict you to enter one character.

Because I want to compare the size of two numbers so I use 2 read, but why do I have to add an echo in the middle "?" Because if you don't add that read and continue to let you enter $y after you've entered the $x line, it's all about beauty.

echo "" >/dev/null
Why is the output empty I said, but why should I be directed to the "black hole", because if I do not enter anything then my script will have a message, I do not want to see him, so I directed him to the "black hole".

If [-N $x-N $y]
Then

Fi

This is an if judgment,-N is not empty,-a conditional statement (both sides are satisfied only), this sentence is judged only you two times the input is not empty, then will be executed, otherwise.

if [["$x $y" =~ ^[0-9]+$]
Then

Fi

This is a digital judgment, judging whether you are typing is a number, because if you enter the letter, then the system may be twos code to compare the meaningless. So I have to decide if it's a number. (here, in particular, I've put $x$x all together for comparison.) Otherwise it will be judged, waste of memory)

If [$x-gt $y]
Then
echo "$x > $y"
elif [$x-eq $y]
Then
echo "$x = $y"
Else
echo "$x < $y"
Fi

This is the judgment of the numbers. I'm going to judge the two numbers I've entered. -eq equals-gt greater than-lt less than-ge greater than or equal to-le less than equals.

This article is from my study blog, so be sure to keep this source http://shuai12138.blog.51cto.com/10118203/1901603

Comparison of if judgments of the shell