Tips Of Bash

`` will create a string from shell command stdout,such as `today=date +%Y-%m-%d`, it’s same as today=$(date +%Y-%m-%d).
”” will quote the literal string with bash or regular expression expand,such as sed "s/$var/string/g" will extent $var as bash variable.
” will quote the literal string without bash or regular expression expand,it means the literal string is the final literal string,such as sed 's/$var/string/g' will not extent $var.