regex explanation code example

Example 1: regex usage

regex usage examples

Example 2: regex

Let regex;
/* shorthand character classes */
regex = /d/; // matches any digit, short for [0-9]
regex = /D/; // matches non-digits, short for [^0-9]
regex = /S/; // matches non-white space character
regex = /s/; // matches any white space character
regex = /w/; // matches character, short for [a-zA-Z_0-9]
regex = /W/; // matches non-word character [^w]
regex = /b/; // Matches a word boundary where a word character is [a-zA-Z0-9_]
These meta characters boast a pre-defined meaning and make various typical patterns easier to use.
/* matching using quantifiers */
regex= /X./; // matches any character
regex= /X*/; // Matches zero or several repetitions of letter X, is short for {0,}
regex= /X+-/; // matches one or more repetitions of letter X, is short for {1,}
regex= /X?/; // finds no or exactly one letter X, is short for is short for {0,1}.
regex= // d{3}; // matches three digits. {} describes the order of the preceding liberal
regex= // d{1,4} ; // means d must occur at least once and at a maximum of four
A quantifies helps developers to define how often an element occurs.
/* character ranges */
regex = /[a-z]/; // matches all lowercase letters
regex = /[A-Z]/; // matches all uppercase letters
regex = /[e-l]/; // matches lowercase letters e to l (inclusive)
regex = /[F-P]/; // matches all uppercase letters F to P (inclusive)
regex = /[0-9]/; // matches all digits
regex = /[5-9]/; // matches any digit from 5 to 9 (inclusive)
regex = / [a-d1-7]/; // matches a letter between a and d and figures from 1 to 7, but not d1
regex = /[a-zA-Z]/; // matches all lowercase and uppercase letters
regex = /[^a-zA-Z]/; // matches non-letters
/* matching using anchors */
regex = / ^The/; // matches any string that starts with “The”
regex = / end$/; // matches a string that ends with end
regex = / ^The end$/; // exact string match starting with “The” and ending with “End”
/* escape characters */
regex = / a/; // match a bell or alarm
regex = / e/; // matches an escape
regex = / f/; // matches a form feed
regex = / n/; // matches a new line
regex = / Q…E/; // ingnores any special meanings in what is being matched
regex = / r/; // matches a carriage return
regex = / v/; // matches a vertical tab
It is critical to note that escape characters are case sensitive
/* matching using flags */
regex = / i/; // ignores the case in pattern ( upper and lower case allowed)
regex = / m/; // multi-line match
regex = / s/; // match new lines
regex = / x/; // allow spaces and comments
regex = / j/; // duplicate group names allowed
regex = / U/; // ungreedy match

Example 3: regex examples

\d         matches a single character that is a digit -> Try it!\w         matches a word character (alphanumeric character plus underscore) -> Try it!\s         matches a whitespace character (includes tabs and line breaks).          matches any character -> Try it!

Example 4: regex examples

abc*        matches a string that has ab followed by zero or more c -> Try it!abc+        matches a string that has ab followed by one or more cabc?        matches a string that has ab followed by zero or one cabc{2}      matches a string that has ab followed by 2 cabc{2,}     matches a string that has ab followed by 2 or more cabc{2,5}    matches a string that has ab followed by 2 up to 5 ca(bc)*      matches a string that has a followed by zero or more copies of the sequence bca(bc){2,5}  matches a string that has a followed by 2 up to 5 copies of the sequence bc

Example 5: regex examples

\D         matches a single non-digit character -> Try it!