Let’s learn Regular Expression -2

                                       Let’s learn Regular Expression -2

We already covered “Backslash, Pipe & Question Mark. 
Lets continue with next list expression

·   Parentheses ()

Parentheses () in Regular Expressions work the same way that they do in mathematics.

Let’s try with example,

/test(one|two)/cab

Now we consider “Order of Operations” we used in math.

Without Parentheses, 2 + 3 x 5 = 17 

With Parentheses, (2 + 3) x 5 = 25

This is how paranthese impact the order of operation in math. Now let’s go to Regular expression /test(one|two)/cab

this regex to match either the cab page in testone or the thanks page in testtwo – and

it is the parentheses that allow us to group so that the pipe knows what to choose between.

Let’s do one example.

we’re going to roll two URLs into one goal, but this time, we use the parentheses to tell the question mark what is optional. This website has three thank-you pages:

thanks

thankyou

thanksalot

If we only want the thanks and the thanksalot pages to be part of our goal,

 we could do it like this: thanks(alot)? This means, the target string must include thanks, but alot is optional. So it matches both thanks and thanksalot. And the thankyou page will never get included, because there is no s in its URL so it doesn’t match the beginning of this RegEx, i.e.thanks.

·   Square Brackets & Dashes

With use of Square Brackets, we can create  a simple list, like this: [aiu] . This is a list of items and includes three vowels only.

So, p[aiu]n will match pan, pin and pun. But it will not match pain, because that would require us to use two items from the [aiu] list, and that is not allowed in this simple example. You can also use a dash to create a list of items, like this:

[a-z] – all lower-case letters in the English alphabet

[A-Z] – all upper-case letters in the English Alphabet

[a-zA-Z0-9] – all lower-case and upper-case letters, and digits.

Dashes are one way of creating a list of items quickly, as you can see above. (Note that they are not separated by commas.)

·     Braces {}

Braces repeat the last “piece” of information a specific number of times.These can be used with two numbers, like this: {1,3}, or with one number, like this: {3}.

{x,y }, :  When there are two numbers in the braces, such as {1,3}, it means, repeat the last “item” at least 1 time and no more than 3 times.

{z}:  When there is only one number in the braces, such as {3}, it means, repeat the last item exactly 3 times

Let’s see it by one example,

we have a scenario where, a page has 10-digit mobiles number are displayed and we have to match all the mobile number using regEx. We could write a regEx as below:

\d{10}:\d is basically used to match a single digit.

This regEx exactly matches 10 digits as defined in the braces.

I will continue this topic in another post. Please click in “Regular Expression 3” for further list of expression.

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

Regular Expression 1

Regular Expression 3

Happy Testing!!!