Your question suggests a logical confusion. One can't store a subroutine in a scalar variable. You can store a reference to a subroutine in a scalar variable, or you can, as in your code, store the name of a subroutine in a scalar variable.

In the former case, the answer to your question is easy:

my $coderef = \&some_sub;  # $coderef contains a reference to &some_su
+b
my $results = $coderef->();
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In the latter case, you can either use eval:

my $subname = 'some_sub';
my $results = eval "$subname()";
die $@ if $@;
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my $results = do { no strict 'refs'; $subname->() };
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use strict;
use warnings;

sub some_sub {
  print "Hello world!\n";
  return 42;
}

my $coderef = \&some_sub;
my $subname = 'some_sub';

print $coderef->(), "\n";
print eval "$subname()", "\n";
die $@ if $@;
print do { no strict 'refs'; $subname->() }, "\n";

__END__
Hello world!
42
Hello world!
42
Hello world!
42
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But storing names of subroutines in variables should be a red flag to alert you that you are probably not thinking about the problem in the right way.