Re: Hurdle with summarizing results from complex data structure related to MySQL result handling

[Athanasius]

Hello hiyall,

Feedback and critique is welcome.

roboticus has already provided an excellent answer, so I’ll just comment on one aspect of your code:

my($grant,$db,$schema,$user,$scope) = $results[0] =~ m/.*GRANT\s(.+)\s
+ON\s(.+)\.(.+)\sTO\s(\S+)\@(\S+)/ix;
if (defined $user && length $user > 0) {
  if (defined $db && length $db > 0) {
    $db =~ tr/'`//d;
  }
  if (defined $schema && length $schema > 0) {
    $schema =~ tr/'`//d;
  }
  if (defined $user && length $user > 0) {
    $user =~ tr/'`//d;
  }
  if (defined $scope && length $scope > 0) {
    $scope =~ tr/'`//d;
  }
  ...
}

First, there is no point in testing the length of each string, because the capture groups are all quantified with a +, meaning “one or more” — so if a match succeeds at all (defined is true), the length must be at least 1.

Second, there is no point in separately testing whether each string is defined, as the regex — any regex — either succeeds or it fails, so either all the match strings are defined, or none of them are.¹

Third, note that the trailing /x does nothing here, as you don’t have any whitespace in the regex.

So the above code can be better written like this:

if (my ($grant, $db, $schema, $user, $scope) = $results[0] =~ /.*GRANT
+\s(.+)\sON\s(.+)\.(.+)\sTO\s(\S+)\@(\S+)/i)
{
    $db     =~ tr/'`//d;
    $schema =~ tr/'`//d;
    $user   =~ tr/'`//d;
    $scope  =~ tr/'`//d;
    ...
}

¹Update: Except in the cases where the captures are optional, either because zero matches are allowed: X?, X*, X{0,5}; or because the captures are part of an alternation: (?:(X)|(Y)). Thanks to AnomalousMonk for explaining this, below.

Hope that helps,

[AnomalousMonk]

... any regex ... either succeeds or it fails, so either all the match strings are defined, or none of them are.

A minor cavil: capture groups that are not required to match for an overall match will return undef in their respective $n capture variables and in list context.

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my $s = 'abc';
 ;;
 my @captures = $s =~ m{ (?: (a)(b)(c) | (w)(x)(y)) (z)? }xms;
 dd \@captures;
"
["a", "b", "c", undef, undef, undef, undef]

The  (?|pattern) construct available with Perl version 5.10 (see Extended Patterns in perlre) modifies this behavior in alternations, but you may still be left with undefs from other sources.

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"use 5.010;
 ;;
 my $s = 'abc';
 ;;
 my @captures = $s =~ m{ (?| (a)(b)(c) | (w)(x)(y)) (z)? }xms;
 dd \@captures;
"
["a", "b", "c", undef]