Written September 23, 2012. Tagged Regular expressions.
For some reason, people often seem to confuse
 in regular expressions.
Say you want to match only the strings "bar" and "car".
I sometimes see this mistake:
It will indeed match "bar" and "car" as intended. But it will also match "|ar".
Round brackets do grouping (and capture groups, and some other things). Within the group, you can use
| for alternation. So this would work as expected:
But square brackets are not the same as round brackets. Square brackets are syntax sugar for character-level alternation.
[abcd] effectively expands to
So if you do
[b|c], that's syntax sugar for
(b|\||c). Probably not what you want.
Instead do this: