How to match a word that is not preceded by "=" using Regex?

Question

I would like to extract symbols from Fortran codes in Ruby. The symbols would have the following patterns (NOTE: the variable type and attribute parts have been filtered out):

a = b, c(2)       ! Match result should be "a" and "c"
d(3) = [1,2, &    ! Match result should be "d"
  3]

The Regex that I have tried is ((?<!=)\w+(?![^\[]*\]+)(?=( |,|\(|$))) with lookaround stuffs. But due to the restriction of lookbehind, I can not match "= *" to exclude b.

I used Rubular for testing. For your convenience, see here.

Thanks in advance!

Answer 1

In order to make your regex work you can first replace all trailing whitespace after =

.gsub(/=\s+/, '=').scan(/((?<!=)\w+(?![^\[]*\]+)(?=( |,|\(|$)))/)

Answer 2

One easy thing you could do is split the line in two (at the '=') and only do your regex on the left operand.

That way you don't have to write any complex regex.

Answer 3

My advice would be to separate your regex into 2 expressions. Regex needn't always be a one-liner.