Remove the slashes, extract the modifier ("i") (say, in a variable $flags). Keep the core of the regex as a string, in your example that would be .*uba$.

Then put "(?$flags:" in front of it, and ")" behind it. You can use that string ($re) directly as a regex: 

$re = "(?:$flags:$core)";
if($input =~ $re) { ... }

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edit Oops, one too many colons: 
$re = "(?$flags:$core)";
if($input =~ $re) { ... }

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You can also turn it into a regex object: 
$qr = qr/$re/;

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In reply to Re: creating qr from existing regex by bart
in thread creating qr from existing regex by Bobert1234

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