regularexpressions's Introduction

Regular Expressions

Resources

Tester https://regex101.com/
Tester http://regexr.com/
Tutorial http://www.regular-expressions.info/
Interactive Tutorial http://regexone.com/
Puzzles https://regexcrossword.com/

Notes

Available in many programming languages and text editors

Useful for developers and power users
Different syntax in Visual Studio

Easier to write than to read

Comments are important
Explain why you're doing what you're doing

Write pseudo code first

Break down the logic
Think about edge cases

Testing

List strings that should match
List similar strings that shouldn't match

Libraries are available online

Don't reuse without testing
Add comments if there aren't any

Format

/regex/flags
Regex is bracketed by slashes

Modifiers (flags)

i Case insensitive
g Global (don't return on first match)
m Multi-line (treat each line as a separate string)

Examples

Phone numbers /\(?\d{3}\)?( |-)?\d{3}( |-)?\d{4}/g

should match:
4055991234
(405) 599-1234
405-599-1234
405 599 1234

should not match:
405599123
40-55991234

Words without vowels /\b[^aeiouy ]+\b/ig

should match:
Ths is a tst.

should not match:
This is a test.

Word characters repeated 3+ times /(\w)\1{2}/ig

should match:
teeest
test___test
test000test

should not match:
teest
te e est

Repeated words /(\b\S+)\s+\1\b/ig

should match:
This is is a test.
This is IS a test.
This isn’t isn’t a test.

should not match:
This is isn’t a test.

Two spaces between sentences /[.?!] {2,}(?=[A-Z])/g

should match:
This should match.  It has two spaces.
This should match?  It has two spaces.
This should match!  It has two spaces.
This should match.   It has three spaces.

should not match:
This should not match. It only has one space.
This     Should not match.