Let’s learn Regular Expression -3

                               Let’s learn Regular Expression -3

Regular expression is an interesting topic but very vast one.

This is my third post for regular expression.

·     Dot (.)

A dot matches any one character.

Ultimately represents numeric, alpha, special character. And a dot even matches a whitespace.

Let’s see an example

.ar

It would match car, tar, bar. It would also match %ar and #ar (because % and # are characters, too.)

However, it wouldn’t match ar. Why not? A dot matches one character, and ar includes zero characters for the dot to match (i.e., it didn’t match any).

·    The Plus Sign (+)

A plus sign matches one or more of the former items.

Let see an example

Aaargh! :

Aaaargh! 

Aaaaaaaaargh

argh

Now we write regex aa+rgh

That will match aargh and aaargh and Aaaaaaaaargh

however, that it won’t match argh since + says one or more of the former items.

·   Star (*)

* function just like plus signs, except they allow us to match ZERO (or more) of the previous items

Lets consider same example of + plus

Aa*rgh

It will match all four strings from above example

·    Dot Star (. *)

There are two Regular Expressions that, when put together, mean “get everything.” They are a dot followed by a star, like this:

testing. *one\.php

In this example, regex will match to everything that starts with testing and ends with one.php . This means if you have pages in the testing directory that end with .html, they won’t be a match to the above RegEx.

This expression is also known as “Greedy expression”. I would explain in another post

·   Caret (^)

a caret in Regular Expression, force the Expression to match only strings that start exactly the same way RegEx does.

 Let’s see one example if website page contains strings that start with a number at the beginning such as:

123test

114test

143test

We need to match only the digits at the staring of the string.

let’s write a regex:

(^\d+)

Here ^ indicates beginning of the string.

        \d denotes matching a single digit.

        +  denotes matching of one or more digits.

·     Dollar Sign ($)

A dollar sign means doesn’t match if the target string has any characters beyond where I have placed the dollar sign in my Regular Expression.

·   Whitespace (\s)

Matches a whitespace character, which in ASCII are tab, line feed, form feed, carriage return, and space; in Unicode, also matches no-break spaces, next line, and the variable-width spaces (amongst others).

·     Digits(\d)

Matches a single digit,same as [0-9] in ASCII; When used with combination of regular expression such as \d+ will match one or more digits in a line or string.

To start with regular expression learning, please go through previous posts by clicking on these links.

Regular Expression 1

Regular Expression 2

Happy Testing!!!