Regular expressions are a strings of (regex) code and matching (character) references used for finding patterns of characters within some defined contiguous string of characters (ie. forms validation, an IDE identifying opening and closing tags in markup code or a terminating semicolon in Java/C#). A more official definition describes regex as:
Having more than a passing familiarity with regex can be a tremendous help when doing any kind of development related to the identification of patterns in character/symbol data. When you understand how each component works you can very easily begin to build your own expressions to suit your particular application's pattern matching needs.
Below are some common regular expressions:
Alphanumeric Strings and Chars
^\w+$
Username (16 characters)
/^[a-z0-9_-]{3,16}$/
Hexadecimal ID
/^#?([a-f0-9]{6}|[a-f0-9]{3})$/
Email
/^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/
URL
/^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$/
ipV4 Address
/^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/
HTML Tag
/^<([a-z]+)([^<]+)*(?:>(.*)<\/\1>|\s+\/>)$/
XML Tags
Don't use Regex, use something like XPath
Just remember that the brackets are regex matching patterns, the curly braces are index positioners, the parens surround regex "capture groups" and the other syntax denotes flags for how much to match and other special conditions to be applied to the match/regex expression. Go here to practice and learn more: https://regexr.com/
The above illustrates Regex in 2 Capture Groups, One for alpha chars and the other for numeric chars
Reference: https://code.tutsplus.com/tutorials/8-regular-expressions-you-should-know--net-6149
"In computing, regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters. Regular expressions (abbreviated as regex or regexp, with plural forms regexes, regexps, or regexen) are written in a formal language that can be interpreted by a regular expression processor, a program that either serves as a parser generator or examines text and identifies parts that match the provided specification."
This diagram breaks down the gist of how an expression works- see the reference below for full list of matching modifiers and syntax
Having more than a passing familiarity with regex can be a tremendous help when doing any kind of development related to the identification of patterns in character/symbol data. When you understand how each component works you can very easily begin to build your own expressions to suit your particular application's pattern matching needs.
Below are some common regular expressions:
Alphanumeric Strings and Chars
^\w+$
Username (16 characters)
/^[a-z0-9_-]{3,16}$/
Hexadecimal ID
/^#?([a-f0-9]{6}|[a-f0-9]{3})$/
/^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/
URL
/^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$/
ipV4 Address
/^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/
HTML Tag
/^<([a-z]+)([^<]+)*(?:>(.*)<\/\1>|\s+\/>)$/
XML Tags
Don't use Regex, use something like XPath
Just remember that the brackets are regex matching patterns, the curly braces are index positioners, the parens surround regex "capture groups" and the other syntax denotes flags for how much to match and other special conditions to be applied to the match/regex expression. Go here to practice and learn more: https://regexr.com/
Reference: https://code.tutsplus.com/tutorials/8-regular-expressions-you-should-know--net-6149
