regex101: PCRE (Legacy) Match Workspace

^start of line

Non-Capturing Group(?:dog(?:, |$))*

*repeats the group contents below any number of times:

dogthe literal text dog (case sensitive)

Non-Capturing Group(?:, |$)

1st Alternative,

, the literal text ,

2nd Alternative$

$end of line

Non-Capturing Group(?:cat)?

?repeats the group contents below at most once:

catthe literal text cat (case sensitive)

$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

25 tokens

Regular Expression

^(?:dog(?:, |$))*(?:cat)?$

New

cat
dog, cat
dog, dog, cat
dog, dog, dog
dog, dog, dog, cat
dog, dog, dog, dog, cat
dog, dog, dog, dog, dog
dog, dog, dog, dog, dog, cat
dog, dog, dog, dog, dog, dog, dog, cat
dog, dog, dog, dog, dog, dog, dog, dog, dog

Extraction

cat
dog, cat
dog, dog, cat
dog, dog, dog
dog, dog, dog, cat
dog, dog, dog, dog, cat
dog, dog, dog, dog, dog
dog, dog, dog, dog, dog, cat
dog, dog, dog, dog, dog, dog, dog, cat
dog, dog, dog, dog, dog, dog, dog, dog, dog