Several simple expressions that are common to regular expressions

Regular expressions are also called regular expressions, and sometimes we will call it "Mars text", because when you write, then go to see, often will not understand, although it is so, but because it has a powerful function, so become our essential knowledge, the following describes a few common expressions:

Integer or decimal: ^[0-9]+\. {0,1} [0-9] {0,2}$
Only numbers can be entered: "^[0-9]*$".
Only n digits can be entered: "^\d{n}$".
Only numbers with at least n digits can be entered: "^\d{n,}$".
You can enter only the digits of the m~n bit:. "^\d{m,n}$"
Only numbers starting with 0 and non-0 can be entered: "^ (0|[ 1-9][0-9]*) $ ".
You can only enter a positive real number with two decimal places: "^[0-9]+ (. [ 0-9]{2})? $ ".
You can only enter a positive real number with a decimal position: "^[0-9]+ (. [ 0-9]{1,3})? $ ".
You can only enter a non-zero positive integer: "^\+?" [1-9] [0-9]*$].
You can only enter a non-zero negative integer: "^\-[1-9][]0-9" *$.
Only characters with a length of 3 can be entered: "^. {3}$ ".
You can only enter a string consisting of 26 English letters: "^[a-za-z]+$".
You can only enter a string consisting of 26 uppercase English letters: "^[a-z]+$".
You can only enter a string consisting of 26 lowercase English letters: "^[a-z]+$".
You can only enter a string consisting of a number and 26 English letters: "^[a-za-z0-9]+$".
You can only enter a string consisting of a number, 26 letters, or underscores: "^\w+$".

It is difficult to write regular expressions with very high matching degrees, so it is advisable to write in conjunction with the plugin to improve the efficiency of the work (of course, personal opinion).

Several simple expressions that are common to regular expressions