The difference between single quotation mark, double quotation mark and back quotation mark in shell script

When defining a variable , There can be no spaces on either side of the equal sign , If there are spaces, double quotation marks or single quotation marks can be used to combine the contents of variables .

（1） Special characters in double quotation marks can keep their original characteristics

var="lang is $LANG"
echo $var
-- Output --
lang is en_US

（2） Special characters in single quotation marks are only general text

var='lang is $LANG'
echo $var
-- Output --
lang is $LANG

• Special characters （ Include spaces ） Also available "\" Escape to general character

（3） The quotation marks ： Some instructions require information from other instructions , You can use ` Instructions ` or $( Instructions ), The latter is recommended

version=`uname -r`  or  version=$(uname -r)
echo $version
-- Output --
5.4.0-77-generic