This is a regular expression (regex) tutorial to demonstrate basic definitions of commonly used parameters in programming. These expressions are powerful and flexible tools to either find or find-and-replace search patterns in strings.
Regex uses the following program to match a given URL:
/^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$/
Using this line, we are able to determine the validity of the entered website address. This enables the programmer to validate URLs in practically any app or program that they need.
- Anchors
- Quantifiers
- Grouping Constructs
- Bracket Expressions
- Character Classes
- The OR Operator
- Flags
- Character Escapes
The sequence of characters may look random and meaningless at first glance. However, by breaking it down, we can follow the underlying logic and usefulness in specifying our needs.
The URL matching sequence is bracketed by two particular characters: ^ and the start and $ at the end. The rest of the code must be contained between these. When using both, we are telling the program to match the exact URL. However, there are a couple of ways to expand its functionality. By using just ^, we can tell it to match any URL that starts with our input. By using just $, we can tell it to match any URL the ends with our input.
Qualifiers tell the program how many times it should identify a particular expression. For instance, ending with a ? tells it to only execute it a single time, whereas a * tells it to execute multiple times. Additionally, curly brackets {} tells the program to look for matches in multiple contexts.
Grouping Constructs are determinde by regular parantheses (). These separate the particular groups of code that you are wanting to match. We can use multiple pairs to evaluate different parts we want to match.
Bracket Expressions allow us to look for certain characters as determinde within []. For example, [abc] looks for a, b, or c within the string. We can also search for other factors, such as whether there's a number before a specific given character (shown by [0-9]%) or whether to match all letters regardless of case (shown by [a-zA-Z]).
There are two character classes for this regex. First is \d, which finds a given digit. Second is \w, which finds a given alphanumeric character.
The OR Operator for this regex is the square bracket, []. This tells the program to match anything you place between the brackets.
Flags are optional and can be used to change the way the search is conducted. For instance, g (aka global) searches for every instance of a match rather than just one. Then, i (aka ignore) instructs the regex to ignore case sensitivity.
Character Escapes are definde by the backslash \ to escape a special character, thus allowing you to use it as a literal. Whereas the double backslash \\ allows you to escape the backslash special character itself.
Andy Williams is a future graduate of the University of Oregon Full-Stack Development Boot Camp. GitHub: https://github.com/andycwilliams