Regular Expressions 101

Pro

examplethe literal text example (case insensitive)

\s+any whitespace character, repeated at least once

Group 1([1-9][0-9]*)

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

Character Class[0-9]*

*matches any number of characters from the set below:

0-9one character from 0 (48₁₀) to 9 (57₁₀)

Non-Capturing Group(?:\s+when\s+([a-z])(?!\s*,\s*\2\b)(?:\s*,\s*[a-z])?)?

?repeats the group contents below at most once:

\s+any whitespace character, repeated at least once

whenthe literal text when (case insensitive)

\s+any whitespace character, repeated at least once

Group 2([a-z])

Character Class[a-z]

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

Negative Lookahead(?!\s*,\s*\2\b)

\s*any whitespace character, repeated any number of times

,the literal , (44₁₀ / 54₈ / 2C₁₆)

\s*any whitespace character, repeated any number of times

\2the text saved by group 2

\ban ASCII word boundary

Non-Capturing Group(?:\s*,\s*[a-z])?

?repeats the group contents below at most once:

\s*any whitespace character, repeated any number of times

,the literal , (44₁₀ / 54₈ / 2C₁₆)

\s*any whitespace character, repeated any number of times

Character Class[a-z]

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

\ban ASCII word boundary

Global pattern flags

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

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

Detailed match information will be displayed here automatically.

25 tokens

example\s+([1-9][0-9]*)(?:\s+when\s+([a-z])(?!\s*,\s*\2\b)(?:\s*,\s*[a-z])?)?\b

New

example 1 when a, b
example 2 when a,a
example 3

example 1 when a, b
example 2 when a,a
example 3