my $pat = qr {
    (?(DEFINE)
       (?<number>    (?: [0-9]+ ))
       (?<sign>      (?: [-+] ))
       (?<expr>      (?: (?&term) (?: \s* [-+] \s* (?&expr))? ))
       (?<term>      (?: (?&factor) (?: \s* [/*] \s* (?&term))? ))
       (?<factor>    (?: (?&number) |
                         (?&sign) \s* (?&factor) |
                        \( \s* (?&expr) \s* \)))
    )
    (?&expr)
}x;

[download]
That will even parse 2*-3, and doesn't require (??{ }), or use re 'eval';.

In reply to Re: RFC: Perl regex to validate arithmetic expressions by JavaFan
in thread RFC: Perl regex to validate arithmetic expressions by Serge314

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