You could look them up in the symbol table, but I'd recommend another approach. Store the list of functions in a hash as a list of subroutine references. Like this:

    my %functions = (
        'ram_usage'  => \&mod_ram_usage,
        'disk_usage' => \&mod_disk_usage,
        ...
    );

    for my $name (keys %functions) {
        $functions{$name}->();
    }
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