What are regular expressions? These are patterns that help us work with text. Regular expressions (regex, regexp) used to match sequences of characters in strings: search, edit, delete any area in large texts, data generation or validation, and so on. Regexes can be used in programming languages, command line interfaces, etc...
For example I want validate email addresses from my domain. The expression will look like this:
^.*\@example\.com$
^ symbol means the beginning of an expression.
Next symbols .* need for matching any address in @example.com domain.
Backslash before "at" symbol need for validate @ as is. The same situation with \. symbols.
$ - end of expression.
Result:
Next case need for validation phone numbers. I need accept numbers only from my region. In my case numbers started from +77. I should use this expression:
^\+77\d{1,9}$
^ symbol means the beginning of an expression.
\+ - using "plus" symbol as "plus" symbol.
\d - presents d as digits.
In curly brackets {1,9} digits length.
$ - end of expression.
Result:
Additionally maybe validation when phone number starts from "+77" or "87":
^(\+77|87).?\d{1,9}$
(\+77|87).? - number starts from +77 or 87.
Result:
Now let's look at IP address validation. For verification IP addresses you may use this expression:
((25[0-5]|(2[0-4]|1\d|[1-9]|)\d)\.?\b){4}
Result:
Thanks for regex101.com site, which allowed test my regular expressions.
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