Question

I’ve got a pretty long regex to match an entry in a list I’m processing. The list should be one or more of these entries, comma-separated. Consider a regex:

([abc]+|[123]+)

for the entry. To match my comma-separated list, I’m matching against something like this:

([abc]+|[123]+)(,([abc]+|[123]+))*

(It looks especially foolish with my nasty regex instead of the short one I used here for the example)

I feel there must be a better way than having two copies of the entry — once for the first entry, again for and follow comma/entry pairs.

Answer 1

Something like this perhaps:

((?!=^|,)([abc123]))+

Broke down it’s:

(                       # start of parent capture
  (?!=^|,)                # look ahead and find either the start of a line or a comma
  ([abc123])              # actual pattern to look for (token)
)+                      # say this whole pattern is repeatable

PHP Demo (Was simplest way to demonstrate)