I should add that if the script reads values of $regex or $subst from an
external source, then my use of eval is seriously flawed. For example, that
external source might provide this value for $subst:
/; system("do-bad-things"); qr/x/
The eval will execute the "do-bad-things" command on your system.
-----Original Message-----
From: Claude Brown via beginners <beginners@perl.org>
Sent: Thursday, October 26, 2023 8:07 AM
To: Levi Elias Nystad-Johansen <levi.johan...@protonmail.com>; Andrew Solomon
<and...@geekuni.com>
Cc: Josef Wolf <j...@raven.inka.de>; beginners@perl.org
Subject: RE: Using qr// with substitution and group-interpolation in the
substitution part
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Josef,
Inspired by Levi's “eval” idea, here is my solution:
sub substitute_lines {
my ($contents, $regex, $subst) = @_;
eval "\$contents =~ s/$regex/$subst/g";
return $contents;
}
$data = "foo whatever bar";
$data = &substitute_lines($data, qr/^foo (whatever) bar$/m, 'bar $1 baz');
print "$data\n";
The differences:
- escaped the "$" so the eval gets a literal "$contents"
- didn't escape "$" so the eval receives the value of $regex and $subst
- moved the "g" into the sub as it has no meaning for a qr//
- removed the "m" from the sub as it best left with the original qr//
- added "$data = ..." to get back the value from the subroutine
Cheers,
Claude.
