Conditional regex in vim?

Question

Is it possible to do conditional regex (like the one described in http://www.regular-expressions.info/conditional.html) in Vim?

Answer 1

Not natively, however if you have +perl in vim you should be able to use

:perldo s/search/replace/

Answer 2

The vim docs state that vim's regexes don't support the conditional expressions (in a section comparing vim's pattern support with perl's):

Finally, these constructs are unique to Perl:
- execution of arbitrary code in the regex: (?{perl code})
- conditional expressions: (?(condition)true-expr|false-expr)

Answer 3

Vim regex does not have this feature, so you will need to use a bit of repetition to create the same behaviour:

/\(\%(condition\)\@=then\|\%(condition\)\@!else\)

Note that you have to use the condition twice in the Vim version and the lookahead/lookbehind must always be the opposite in the then/else parts otherwise your regex will not be correct.