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In Perl, the parentheses define what you are capturing. With (.*) you are capturing everything up to the semicolon, therefore you get everything except the leading MODULE into $1. Depending on how your input varies, you could use one of the following:

  my $MODULE_NAME = 'MODULE C17 (N1, N2, N3, N6, N7, N22, N23);';
# Capture MODULE and the first "word" after MODULE
  if (defined($MODULE_NAME) && ($MODULE_NAME =~ /(MODULE \w+) /)) 
# Capture everything before the opening parenthesis, without spaces
# if (defined($MODULE_NAME) && ($MODULE_NAME =~ /^(.*?)\s+\(/))
     {
         my $module_name = $1;
         print "Module name = $module_name\n";  
     }
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Note that in the second regex I had to escape the opening parenthesis to tell Perl that this is the character ( and not the start of a new capturing group.