regex noob question : a(b|c) and a[bc] same ?

hottdogg · 03-28-2008, 09:31 AM

what's the difference between these patterns:
a(b|c) and a[bc] ?

I supposed there's no difference but plz CMIIW..
Tnx.

matthewg42 · 03-28-2008, 09:37 AM

There are multiple implementations of regular expressions. There can be be subtle differences. For example, in perl REs, the former will make available the portion in parenthesis in the $1 variable, and the second won't.

Which sort of RE are you talking about?

ta0kira · 03-28-2008, 10:04 AM

In this case there is no difference, but that's just a coincidence. The first allows you to have multiple-character alternatives whereas the second doesn't, but allows you to exclude individual characters. For example:

Code:

a[bc] == a(b|c) == (ab|ac)
ab[cde] == ab(c|d|e) == a(bc|bd|be)
a[^bc] == (doesn't convert)
(doesn't convert) == (ab|cd)

ta0kira