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Re^2: Using SprintF in S & R

by afoken (Canon)
on Jul 11, 2017 at 20:37 UTC ( #1194868=note: print w/replies, xml ) Need Help??


in reply to Re: Using SprintF in S & R
in thread Using SprintF in S & R

The right hand side of s/// does not execute code unless you use the "e" modifier.

Would you bet your money on that statement? I would not.

You are right, s/// usually does not execute code without the /e modifier. But Perl would not be Perl if you could not mess around with that. Note that even if you could mess with perl, you probably should not.

I'll abuse a trick invented by Andrew Pimlott, that I saw first in the "Perl hardware store" talks (1, 2, 3, 4) by Dominus:

#!/usr/bin/perl use strict; use warnings; sub TIEHASH { return bless {},$_[0]; } sub FETCH { return $_[1]; } tie my %X,__PACKAGE__; my $foo='look! no eval: 3735928559'; $foo=~s/(\d+)/$X{sprintf '0x%08X',$1}/; print $foo;
>perl eval.pl look! no eval: 0xDEADBEEF >

But there is also a way without tie magic. Dereferencing an anonymous array reference:

#!/usr/bin/perl use strict; use warnings; my $foo='look! no eval: 3735928559'; $foo=~s/(\d+)/${[sprintf '0x%08X',$1]}[0]/; print $foo;
>perl eval2.pl look! no eval: 0xDEADBEEF >

Both tricks (ab)use the fact that s/// interpolates the replacement expression, unless you force it not to do so (using ' as the delimiter instead of /).

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

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