Re: Regex: first match that is not enclosed in parenthesis

> and I need to find the first occurrence of "+" that is not enclosed within parenthesis, i.e. the one before "5", how would I do that with a regular expression ?

depends what you mean with "finding"!

If it's just the position you need, a simple technique I like is to replace all inner paren-pairs till you get a "cleaned" string and then to try finding whatever it needs.

This demonstrates the intermediate results:

  DB<172> $s=$s0
 => "1*((2+3)*((3+4)+5))*(6+7)+8"

  DB<173> print "$s\n" while $s =~ s# \( [^()]* \) # '.' x length($&) 
+#gex 
1*(.....*(.....+5))*.....+8
1*(.....*.........)*.....+8
1*.................*.....+8

  DB<174> index $s, '+'
 => 25
[download]

Cheers Rolf

( addicted to the Perl Programming Language)

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Re^2: Regex: first match that is not enclosed in parenthesis by monkprentice (Novice) on Jun 30, 2013 at 13:53 UTC
Finding in my case means to return the prefix and postfix substrings. I also thought of this. This way one could just find the substring before and after the retrieved position. Good Idea.	[reply]
Re^3: Regex: first match that is not enclosed in parenthesis by hdb (Monsignor) on Jun 30, 2013 at 16:53 UTC
Something like this: `use strict; use warnings; my $input = "1(2+3)(3+4)+5*(6+7)"; my $level = 0; my $tab = "\| "; my %action = ( '(' => sub { print "\n", $tab x ++$level, shift }, ')' => sub { print "\n", $tab x $level--, shift }, '+' => sub { print "This one>>>" unless $level; print +shift }, 'default' => sub { print shift }, ); ( $action{$_} // $action{'default'} )->($_) for $input =~ /./g;` [download] The additional effort is only worthwhile if you have ambitions beyond your initial question.	[reply] [d/l]
Re^3: Regex: first match that is not enclosed in parenthesis by LanX (Saint) on Jun 30, 2013 at 16:23 UTC
Sounds like what you really need is a lexer. hdb regularly posts such solutions based on dispatch tables, worth searching for... HTH! =) Cheers Rolf ( addicted to the Perl Programming Language)	[reply]