Regular Expressions 101

Positive Lookbehind(?<=,|^)

1st Alternative,

,the literal , (44₁₀ / 54₈ / 2C₁₆)

2nd Alternative^

^start of line

Group 1([^,]*)

Negated Character Class[^,]*

*matches any number of characters outside the set below:

,the literal , (44₁₀ / 54₈ / 2C₁₆)

Non-Capturing Group(?:,.*)?

?repeats the group contents below at most once:

,the literal , (44₁₀ / 54₈ / 2C₁₆)

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

Group 2(,\1)

,the literal , (44₁₀ / 54₈ / 2C₁₆)

\1the text saved by group 1

Positive Lookahead(?=,|$)

1st Alternative,

,the literal , (44₁₀ / 54₈ / 2C₁₆)

2nd Alternative$

$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

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

(?<=,|^)([^,]*)(?:,.*)?(,\1)(?=,|$)

New

hello-world,goodbye-world,goodbye-world,hello-world
hello-world,hello-world,goodbye-world,goodbye-world