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Postings from June 2003
"perl-5.8.0@ton.iguana.be (via RT)" wrote:
>
> This code:
> perl -wle '
> sub fun {
> $a = shift;
> print "fun(<$a>)";
> print "unexpectdly matched $& at position @-" if /^de/
> }
> $_ = "ab\nde";
> s/^([\w\W]*)/fun("$1")/e'
>
> outputs (as expected):
> fun(<ab
> de>)
>
> However, this:
>
> perl -wle '
> sub fun {
> $a = shift;
> print "fun(<$a>)";
> print "unexpectdly matched $& at position @-" if /^de/
> }
> $_ = "ab\nde";
> s/^([\w\W]*)/fun("$1")/em'
>
> outputs:
>
> fun(<ab
> de>)
> unexpectdly matched de at position 3
>
> The only difference is the m modifier on the s///
> I didn't expect the "non-reentrant" regex problems here. Until now I
> though the replacement part of a s/// was safe.
>
> Speculation:
> It seems that m modifier propagates to the regex that's used in fun() which
> gets called from the body.
> Presumably one or more modifiers need localizing.
Yes. Good catch. Setting /m on a match or on a substitution is
equivalent to setting the global special variable $* to 1 (locally).
Thus, it will influence the behaviour of all regexps that haven't /m or
/s set in that scope.
The interaction with $*, and the fact that $* can have remote effects,
makes this bug difficult to solve.
A first step would be to make $* lexically scoped (a compile-time hint,
à la $[). Or to get rid of it.
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