On Jul 15, Luca Veraldi said:
>I'm a Computer-Science student and I'm reading a book about Perl,
>Programming Perl III ed. published by O'Reilly. I find regular
>expressions very interesting and I tried to use a regex analyzed in the
>book, the one to check if a string is ()-balanced. I rewrote it to check
>balancing also for [] and {}.
>
>The regex is the following (I'm not so good writing regex, because it is
>the first time I study this argument, so I'm not so sure the following
>is correct or optimized...)
The regex you have written requires Perl 5.6.0 at least. Is your RedHat's
Perl up-to-date?
> qr{(?>([\(\[\{])(?:(?>[^\(\)\[\]\{\}]*)|(??{$re}))*(?(?{$1 eq "("})\)|(?(?{$1 eq
>"["})\]|\})))}ox;
That looks pretty solid to me, except that it's very stingy in what it
allows to be inside balanced parts.
my $balanced;
$balanced = qr%
(?:
(?> [^][(){}]+ ) # non [] () {} chars
|
\[ (??{ $balanced }) \] # [ ... ]
|
\( (??{ $balanced }) \) # ( ... )
|
\{ (??{ $balanced }) \} # { ... }
)*
%x;
if ($text =~ /^$balanced$/) {
# it's balanced
}
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