1. 1) Save the value in another variable, using Readonly if you want to ensure the saved value doesn't get modified.
2. 2) Use a closure.
3. 3) Interpolate the variable in an eval'd anonymous subroutine.

use Readonly;

my $str = 'hi';

# String
Readonly my $STR => $str;

# Closure
my $closure = do { my $var = $str; sub { $var } };

# Evalled Sub
my $anonsub = do {
    (my $var = $str) =~ s/(["\\])/\\$1/g;
    eval qq{sub {"$var"}};
};

$str = 'hello';

print "string = $STR\n";
print "closure = ", $closure->(), "\n";
print "anonsub = ", $anonsub->(), "\n";
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