in reply to how can I combine these expressions?

How about this:
$str =~ s/(^|[^\%](?:\%\%)*)\% (\{)? # Match and capture 1 or 0 braces ([_a-zA-Z]\w*) (?(2)\}) # If there's anything in $2, match en +ding brace /"$1".$env->{$3}/gex; # $3 now instead of $2 here
This takes advantage of perl's conditional matching operator. From perlre:
(?(condition)yes-pattern|no-pattern) (?(condition)yes-pattern) Conditional expression. (condition) should be either an integer in parentheses (which is valid if the corresponding pair of parentheses matched), or lookahead/lookbehind/evaluate zero-width assertion. Say, m{ ( \( )? [^()]+ (?(1) \) ) }x matches a chunk of non-parentheses, possibly included in parentheses themselves.

Replies are listed 'Best First'.
(Ovid) RE(2): how can I combine these expressions?
by Ovid (Cardinal) on Jul 27, 2000 at 03:47 UTC
    I am humbled in the presence of greatness. :) That was slick.
RE: Re: how can I combine these expressions?
by knight (Friar) on Jul 27, 2000 at 20:29 UTC

    Stellar. That's exactly what I needed. Many thanks.

    (Note on some of the replies above: Simple alternation with '|' doesn't work because it includes the braces in the selected part of the regex. Given %{FOO}, we should interpolate $env->{'FOO'}, not $env->{'{FOO}'}.)