Regular Expressions 101

Explanation

Pro

^start of line

Character Class[a-zA-Z]

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

Negative Lookahead(?!.*(['-]).*\1)

.*any character (except for line terminators), repeated any number of times

Group 1(['-])

Character Class['-]

'the literal ' (39₁₀ / 47₈ / 27₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

.*any character (except for line terminators), repeated any number of times

\1the text saved by group 1

Negative Lookahead(?!.* )

.*any character (except for line terminators), repeated any number of times

the literal text

Positive Lookahead(?=.{0,19}$)

.{0,19}any character (except for line terminators), repeated between 0 and 19 times

$end of line

Character Class[a-zA-Z'-]*

*matches any number of characters from the set below:

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

'the literal ' (39₁₀ / 47₈ / 27₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Non-Capturing Group(?: (?<=[a-zA-Z] )[a-zA-Z][a-zA-Z'-]*)*

*repeats the group contents below any number of times:

the literal (32₁₀ / 40₈ / 20₁₆)

Positive Lookbehind(?<=[a-zA-Z] )

Character Class[a-zA-Z]

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

the literal (32₁₀ / 40₈ / 20₁₆)

Character Class[a-zA-Z]

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

Character Class[a-zA-Z'-]*

*matches any number of characters from the set below:

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

'the literal ' (39₁₀ / 47₈ / 27₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Unit Test Summary

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Quick Reference

25 tokens

Regular Expression

^[a-zA-Z](?!.*(['-]).*\1)(?!.*  )(?=.{0,19}$)[a-zA-Z'-]*(?: (?<=[a-zA-Z] )[a-zA-Z][a-zA-Z'-]*)*$

Unit Tests

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