Regular Expressions 101

Pro

^start of line

dogthe literal text dog (case sensitive)

\ba Unicode word boundary

Non-Capturing Group(?:.*\n)+?

+?repeats the group contents below at least once:

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

\na line-feed (newline) character (ASCII 10)

catthe literal text cat (case sensitive)

\na line-feed (newline) character (ASCII 10)

Group 1(.*(?:\n.*)*?)

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

Non-Capturing Group(?:\n.*)*?

*?repeats the group contents below any number of times:

\na line-feed (newline) character (ASCII 10)

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

Positive Lookahead(?=\ndog|\Z)

1st Alternative\ndog

\na line-feed (newline) character (ASCII 10)

dogthe literal text dog (case sensitive)

2nd Alternative\Z

\Zend of string

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

^dog\b(?:.*\n)+?cat\n(.*(?:\n.*)*?)(?=\ndog|\Z)

New

dog 1
wuff
wuff
cat
123
XYZ
dog 1
wuff
wuff
cat
456
ABC
dog 1
wuff
wuff
cat
789

dog 1
wuff
wuff
cat
123
XYZ
dog 1
wuff
wuff
cat
456
ABC
dog 1
wuff
wuff
cat
789