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

Match Information

Detailed match information will be displayed here automatically.

Quick Reference

25 tokens

Regular Expression

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

New

This is aa
This is aa test
aa aa aa aa aa aa aa
This should m'atch
This a-lso'
This is a test
a b
aa
a

This is 4 test
This is aa  test
This' is aa tes

This is aaaa longer test
This sh'o'uld not
This sh-o-uld not

Extraction

This is aa
This is aa test
aa aa aa aa aa aa aa
This should m'atch
This a-lso'
This is a test
a b
aa
a

This is 4 test
This is aa  test
This' is aa tes

This is aaaa longer test
This sh'o'uld not
This sh-o-uld not