regex - Ruby regular expression groups -

i trying match strings might represent ranges somewhere in document can't quite figure out 1 thing groups... have far:

/(^-?[0-9]+)(\.\.+)(-?[0-9]+$)/ 

which matches 1..10, -20...20, -01234567890...-999999999, etc. however, want second group ($2) have value if middle 3 digits instead of two. want like:

=~ -01234567890...-999999999 $1 = -01234567890 $2 = ... $3 = -999999999  =~ 1..10 $1 = 1 $2 = (empty because 2 dots instead of 3) $3 = 10 

any way specify this, make group if it's value?

you can use:

(^-?[0-9]+)(?:(?:[.]{,2})|([.]{,3}))(-?[0-9]+$) 

which put result in second group if 3 ..

explanation:

• ?: - non-capturing group.
• | - or

note (?:[.]{,2}) non-capturing while ([.]{,3}) capture group.