Regular Expressions 101

\ba Unicode word boundary

Negative Lookbehind(?<!\w)

\wa Unicode word character

Group 1((?:north|south)?(?:east|west)?)

Non-Capturing Group(?:north|south)?

?repeats the group contents below at most once:

1st Alternativenorth

norththe literal text north (case sensitive)

2nd Alternativesouth

souththe literal text south (case sensitive)

Non-Capturing Group(?:east|west)?

?repeats the group contents below at most once:

1st Alternativeeast

eastthe literal text east (case sensitive)

2nd Alternativewest

westthe literal text west (case sensitive)

\ba Unicode word boundary

Negative Lookahead(?!\w)

\wa Unicode word character

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.

Search reference

Regular Expression

\b(?<!\w)((?:north|south)?(?:east|west)?)\b(?!\w)

New

The westerly barn is a room. The field is east of the barn.   The stable is northeast of the field. The forest is northwest of the field.