Then you had a syntax error in your code (such as either missing the closing parenthesis, misplacing it (putting it to the right of the slash), or accidentally escaping it (by preceding it with a \). As you can see here, it should just work:

$ perl foo.pl
ServiceCategoryName=foo,bar,baz
my string foo

$ cat foo.pl
use strict;
use warnings;
my $str = "ServiceCategoryName=foo,bar,baz\n";

if ( $str =~ m/^ServiceCategoryName=(.*)/) {
   print $str;

   # Extract the array from "the rest of the line"
   my @array = split /,/, $1;
   print "my string ", $array[0], "\n";
}
else {
    print "Can't find ServiceCategoryName!\n";
}
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...roboticus

When your only tool is a hammer, all problems look like your thumb.