When you enter parameters at the command line, the shell interprets space (or multiple spaces) as an argument separator. To see this, carefully print @ARGV:

#!/usr/bin/perl
{
    $" = "\n";
    print "@ARGV\n";
}
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This will print each argument on a separate line. Then you will see that it isn't your script that is mishandling the args. To put them back together, you could do something like:

my $args = join '', @ARGV;
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Then you can ask the original question about spaces in the regexes. You could use /gu\s*1/ in the first instance. That will match gu followed by optional space followed by 1.

Phil