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I have a Perl file called grabPet.pl and a text file called Pets.txt

Each pet has a number of toys linked to them. So a: cat=5

cat will have 5 toys. They are separated by commas so:

mouse=3, cat=5, dog=9,

i want to output these into a formatted table.

I am not looking for the answer just guidance on how I could approach it?

I am thinking possibly a 2d array but I dont think perl supports it.

open(FILE, "<pet.txt") || die"could not read);

while (<FILE>) {
      push (@lines, $line);
  }

close FILE;

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    Your code won't compile. Show actual code. Commented Dec 5, 2012 at 9:36

2 Answers 2

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I am not looking for the answer just guidance on how I could approach it?

So here are some hints:

  1. make sure your input line doesn't end with a newline
    chomp (my $line = <FILE>);

  2. split your input string:
    my @parts = split /, */ => $line; # split on commas and whitespace

  3. prepare a hash to store your data because it contains key-value-pairs:
    my %data;

  4. loop over your parts:
    foreach my $part (@parts) { ... }

  5. in your loop, split the parts in key and value:
    my ($key, $value) = split /=/ => $part

  6. in your loop, store it in %data:
    $data{$key} = $value;

Note

I leave it to you as an easy exercise to do it with multiple input lines. Also note that you're using open wrong here:

open(FILE, "<pet.txt" || die "could not read");

because the error check won't do what you expect. Replace it by

open(FILE, '<pet.txt') || die "could not read";

or, better readable:

open FILE, '<pet.txt' or die "could not read";

and better use lexical file handles, three arguments and include the real error message:

open my $file, '<', 'pet.txt' or die "could not read: $!";
...
chomp (my $line = <$file>);
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Parsing

If the data is very orderly, you can split on each line. If we split on commata with preceding spaces, we would get the animal-toynum pairs, that we can then split on the equality sign. I would write this:

my %toys = map {split /=/, $_, 2} split /,\s*/, $line;

Interesting bits are the map function and the third argument to split in one case, but not in the other. The reasons for these are documentet in perldoc -f, and stem from list-to-hash coercion that takes place here.

You can then take a reference to the hash and stuff it into an array, like push @array, \%toys. You can then access the element like $array[5]{mouse}, which would give 3 if we just parsed the sixth line.

If the data is more complex, you have to use regexes, e.g

my %toys;
while (my $line = <>) {
  while ($line =~ m{ \G \s* ([\w-]+) =\s* (\d+) (?:,|\s*$) }xgc) {
    $toys{$1} += $2;
  }
}

This would'nt store each line, but automatically sum the toys for each animal.

Data structures

Perl doesn't support multidimensional arrays, but arrays of arrayrefs, which boils down to the same thing.

my @AoA = (
   [1, 2, 3],
   [4, 5, 6],
   [7, 8, 9]
);

The square brackets denote an anonymous array reference, while curlies would denote an anonymous hash reference. perldoc perldata, perldoc perllol, perldoc perlreftut and friends have more information on these.

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