Tips.Regex.md

Regular Express (Regex) Resources

References

• https://en.wikipedia.org/wiki/Regular_expression

Basic Syntax Notes

• | boolean condition (e.g. grey|gray)

• Parentheses are used to define the scope and precedence of the operators (among other uses)

• ? zero or one occurences of the preceding element

• * zero or more occurences of the preceding element

• + one or more occurences of the preceding element

• * match any character

• ^ Matches the starting positon within the string

• . Matches any single character

• [] Matches a single character that is contained within the brackets

  • [a-z] specified a range which matches any lowercase letter
  • [^abc] matches any character that is not "a", "b", or "c"
  • [^a-z] matches any character that is not a lowercase letter from "a" to "z"

• () Defines a marked subexpression (also called a block or capturing group)

• \n Matches what the nth marked subexpression matched

• $ Matches the ending position of the string, or the position just before a string-ending newline

• {n} preceding item is matched exactly n times

• \ escape sequence

• \w word

• \d digit

• \s whitespace

Tutorials

• https://www.tutorialspoint.com/perl/perl_regular_expressions.htm

• https://www.perltutorial.org/perl-regular-expression/

• https://regexone.com/

Interesting Regex Articles

• https://dzone.com/articles/35-examples-of-regex-patterns-using-sed-and-awk-in

• https://medium.com/factory-mind/regex-tutorial-a-simple-cheatsheet-by-examples-649dc1c3f285

Suggested Books

• Mastering Regular Expressions, Third Edition, by Jeffrey E. F. Friedl

Tools

• Notepad++ Plugin

  • https://github.com/viper3400/NppRegExTractor
    • https://github.com/viper3400/RegExTractor

• https://www.regextester.com/

Exemplars

• .at

  • Matches any three-character string ending with "at"

• [hc]at

  • Matches "hat" and "cat"

• [^b]at

  • Matches all strings matched by .at except "bat"

• (?<=\.) {2,}(?=[A-Z])

  • At least two spaces are matched, but only if they occur directly after a period (.) and before an uppercase letter.