RE: Using qr// with substitution and group-interpolation in the substitution part

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 <[email protected]> 
Sent: Thursday, October 26, 2023 8:07 AM
To: Levi Elias Nystad-Johansen <[email protected]>; Andrew Solomon <[email protected]>
Cc: Josef Wolf <[email protected]>; [email protected]
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.