In this tutorial I will be giving a walk through on the functions and expressions of (Regex) also known as Regular Expression.This works well for extracting data from a specific body of code and can also be used as a validation tool. A regular expression (Regex) is a group of characters that, when used in a search algorithm or code, defines a particular type of search pattern.Regex can be used any time to query string-based data such as: Parsing user input, Examining server or program logs, Analyzing command line outputs, Handling text files with a consistent syntax, Searching and refactoring code and more!
Today we will take a look at the components of a regular expression or (REGX) used when matching a Email Address. In an email address each chararcter has a set responisbility to validiate that the user is entering an email address in the correct format. The Email Address REGEX looks like this: /^([a-z0-9_.-]+)@([\da-z.-]+).([a-z.]{2,6})$/ and if your wondering how this all works when it comes to email adresses the REGX is searching for two things one being the "@" and after that the "domain" example: gmail, yahoo etc..
- Anchors
- Quantifiers
- OR Operator
- Character Classes
- Flags
- Grouping and Capturing
- Bracket Expressions
- Greedy and Lazy Match
- Boundaries
- Back-references
- Look-ahead and Look-behind
When it comes to Anchors in regular expressions or (REGX) we start off with the REGX being defined as the two forward slashes such as /abc/ which means that the REGX will match anything a starting with 'a' then followed by "c" and so on.
EXAMPLE
- /ABC/
Our next Anchor is ^ which is a function defineing the start of a string were looking to match. you can compare the bottom to this Email Address REGX: /^([a-z0-9_.-]+)@([\da-z.-]+).([a-z.]{2,6})$/
- ^YYYY
Lastly we have $ which is a character used to define to define then of the string.
- YYYY$
We use Quantifiers in REGX to verify that there is more the one occorance in a string but what does this mean? Well here's and example let's say you wanted to veriify that there is two 'p's in the text apple we would write:
- REGEX:[p]{2} :{2} is a quantifier to match exact 2 occurrences of preceding part of Regex.
We can look for certain characters or Character classes in a number of ways. In the EXAMPLE above the REGX has a {2,6} meaning were looking for a character count between 2 and 6.
- {10} The Brackets are used to show that were looking for exactly 10 of that chararcter simular to the example above.
- {10,} a coma is put before it to show are looking for more then 10 of that character
- {10,20} Were looking for a range of 10 - 20.
We define the 'OR' operator as the '|' element in a REGX. I don't believe we have any in our REGX.
We use Charater Classes in REGX to identify a certain charatcer from a specific set of characters. For example in our above Email Address REGX: /^([a-z0-9_.-]+)@([\da-z.-]+).([a-z.]{2,6})$/
- /d is the only character class being used in the REGX but what /d is basically saying is that there is a range bewteen 0-9 meaning it will match any numeric character.
Flags are used as an optional parameter to a REGREX that modifies its behaviour of searching, One alphabetic lowercase character is used to represent a flag. in our REGX above the flag is g which stands for global searching. The G flag allows it to look for all their matches rather then just one.
Grouping and Capturing refers to grouping expressions to help us stay more organized and make it simpler to identify the characters that belong to a particular group we group these expressions using round parentheises.
- In our REGX Example above we have 3 bracket expressions which are: ([a-z0-9_.-]+), ([\da-z.-]+), and ([a-z.]{2,6}).
We use brackets expressions for characters that have a special meaning. The regex engine is instructed to search for character classes contained brackets.
In our Email Address REGX EXAMPLE: it would be [a-z0-9_.-]+), ([\da-z.-]+), ([a-z.]{2,6}).
Greedy matches refers to the match being as long as possible wheres lazy match refers to our match being as short as possible ine our example for matching our Email Address REGX we dont have either.
A word boundary \b is a position where one side is a word character and the other side is not a word character, \b is called a boundary while ^ and $ are considered anchors.
We use Back-References when trying to match the same text as that was previously matched by a capturing group.
- EXAMPLE: if you wanted to match a pair of opening and closing tags, and the text in between, If we put the opening tag into a backreference, we will be able to use the tag name for the closing tag as well.
Theres look behind assertions which are checking what is before your REGX match while look ahead assertions which means to check what is after your match and there is possitive and negative of both.
Hi my names Jayden Taylor I am the author of this toturial and im currently in a boot camp with SMU working to complete my certificate to become a full-stack developer, and if you would like to check out my github profile feel free to follow the link :) https://github.com/Jay1194.