There's a few ways of tackling this problem, depending on your goals. To use a constant as an interpolated value within a regular expression, use the following notation: 
if ($string =~ /${\(TEST)}/) {

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This has the unfortunate consequence of slowing down your regular expression, since it can't be compiled. Using the qr operator is your best bet. You can use japhy's suggested format: 
use constant PATTERN => qr/def/;
if ($string =~ PATTERN) { ... }

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An alternative is to leave the constant in string format, and compile it just prior to executing the regex: 
use constant PATTERN => 'def';
my $regex = qr/${\(PATTERN)}/; #options such as /m can go here.
if ($string =~ regex) { ... }

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This gives you the added benefit of being able to easily print the regex out for debugging purposes.

In reply to Re: Using constants in regexes? by dclayton
in thread Using constants in regexes? by Kozz

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