Regular expression tutorials that everyone can understand

b There are 3 types of brackets in the regular expression "[" and Braces "{". The square brackets "[" are the characters that need to be matched, and the curly braces "{" are the number of matching characters specified. The parentheses "(" are used for grouping.) The C caret "^" indicates the beginning of the regular type. The D dollar sign "$" indicates the end of the regular type. 

Now that you know the 3 syntax above, you can write any validation rule in the world. For example, the following example is a good illustration of how the above 3 regular grammars work in a coordinated way.

Note: There is an error, "()" should be "{}"

Check if the user has entered Shivkoirala?

Shivkoirala

Let's start with the first validation, the characters entered between a-g?

[A-g]

The characters entered are between a-g and the length is 3?

[A-g] {3}

The characters entered are between a-g and the maximum length is 3 minimum length of 1?

[A-g] {1,3}

How do I match a fixed 8-digit number like 91230456, 01237648?

^[0-9]{8}$

How can I verify that the minimum length is 3 with a maximum length of 7, such as: 123, 1274667, 87654?

^[0-9]{3,7}$

How to verify the invoice number like LJI1020, the first 3 is the number of letters remaining 8 digits long?

The first three are the letters:

^[A-Z]{3}

The following is a 8-bit length number:

[0-9] {8}

So the whole expression is:

^[a-z]{3}[0-9]{7}$

Verify that the first 3 bits, such as INV190203 or inv820830, are case-insensitive and the remaining 8 digits are numbers.

In the previous expression, only the first 3 are the lowercase English letters of the invoice number, if we enter the capital letter that will not match. So to make sure the first 3 letters are case-insensitive, we're going to use an expression ^[a-za-z]{3}.

^[a-za-z]{3}[0-9]{7}$

Can we verify the simple URL URL format?

First step: Check if there is www:

^www.

The second step: the domain name must be a length of 1-15 in the English alphabet:

. [A-z] {1,15}

Step three: End With. com or. org:

. (com|org) $

The complete expression is as follows:

^www[.] [A-z] {1,15} [.] (com|org) $

Let's look at how BCD (in fact, the 3 basic syntax above) validates the email format.

The first step: email starts with an English letter of 1-10 in length, followed by an "@":

^[a-za-z0-9]{1,10}@

The second step: at the back of the @ is the English alphabet with a length of 1-10, followed by a "." ：

[A-za-z] {1,10}.

Step three: End With. com or. org:

. (com|org) $

The final complete expression is as follows:

^[a-za-z0-9]{1,10}@[a-za-z]{1,10}. (com|org) $

Verify that the value is in the 0-25 number:

^ ([0-9]) | ([0-1][0-9]) | ([0-2][0-5])) $

Verify that the format is mm/dd/yyyy, YYYY/MM/DD, and dd/mm/yyyy date:

Step

 

Regular

 

Description description

 

First check DD. First DD is 1-29 long ( February), 1-30 (month-small), 1-31 (month-old).

 

So DD is 1-9 or 01-09

 

[1-9]|0[1-9]

 

The

Allows the user to enter 1-9 or 01-09.

 

Add matching 10-19 to DD

 

[1-9]|1[0-9]

 

The

Allows the user to enter 01-19.

 

Add matching 20-29 to DD

 

[1-9]|1[0-9]|2[0-9]

 

The

Allows the user to enter 01-29.

 

I then add a match 30-31 to DD

 

[1-9]|1[0-9]|2[0-9]|3[0-1]

 

The last user can enter 01-31.

 

To match the delimiter for the day period "/", "-"

 

[/.-]

 

The

Allows the user to enter a date separator.

 

mm is a similar operation

 

[1-9]|0[1-9]|1[0-2]

 

The

lets the user enter a month value of 01-12.

 

Last is the action of YY

 

1[9][0-9][0-9]|2[0][0-9][0-9]

 

The

Allows the user to enter the year 1900-2099.

The regular expression for the date in the last dd/mm/yyyy format is:

^ ([1-9]|0[1-9]|1[0-9]|2[0-9]|3[0-1]) [-/.] ([1-9]|0[1-9]|1[0-2]) [- / .] (1[9][0-9][0-9]|2[0][0-9][0-9]) $

Date in MM/DD/YYYY format:

^ ([1-9]|0[1-9]|1[0-2]) [-/.] ([1-9]|0[1-9]|1[0-9]|2[0-9]|3[0-1]) [- / .] (1[9][0-9][0-9]|2[0][0-9][0-9]) $

Date in YYYY/MM/DD format:

^ (1[9][0-9][0-9]|2[0][0-9][0-9]) [-/.] ([1-9]|0[1-9]|1[0-2]) [- / .] ([1-9]|0[1-9]|1[0-9]|2[0-9]|3[0-1]) $

Shortcut commands

You can also use the following shortcut commands to simplify your regular expression:

Actual command

Shortcut commands

[0-9]

D

[A-z] [0-9] [_]

W

Occurs 0 or more times

*

At least one time.

+

Occurs 0 or 1 times

?

Complete the full text.

Regular expression tutorials that everyone can understand