perl regex grouping overload

I am using the following perl regex lines

$myalbum =~ s/[-_'&’]/ /g;
$myalbum =~ s/[,’.]//g;
$myalbum =~ m/([A-Z0-9\$]+) +([A-Z0-9\$]+) +([A-Z0-9\$]+) +([A-Z0-9\$]+) +([A-Z0-9\$]+)/i;

to match the following strings

"30_Seconds_To_Mars_-_30_Seconds_To_Mars"

"30_Seconds_To_Mars_-_A_Beautiful_Lie"

"311_-_311"

"311_-_From_Chaos"

"311_-_Grassroots"

"311_-_Sound_System"

What I am experiencing is that for strings with less than 5 matching groups (ex. 311_-_311), attempting to开发者_运维百科 print $1 $2 $3 prints nothing at all. Only strings with more than 5 matches will print.

How do I resolve this?

It looks like you just want the words in separate groups. To me, it seems like you're abusing regexes to do that when you could just run your substitutions and then split. Just do:

$myalbum =~ s/[-_'&’]/ /g;
$myalbum =~ s/[,’.]//g;
my @myalbum_list = split(/\s/, $myalbum);
#Print out whatever it is you want/ test length, etc...
print "$myalbum_list[0] $myalbum_list[1] $myalbum_list[2]";

the + character means at least one match. Which means your regex m/([A-Z0-9\$]+) +([A-Z0-9\$]+) + ... requires all those fields to be there for it to be considered a match. The reason you are not capturing anything is because it's not actually matching.

You are probably looking for the * character which means zero or more not one or more like +.

I suppose your capturing groups are empty for "311 - 311" because this string doesn't match your regex.

How to resolve? Use * instead of + to permit empty sequences.

Edit: From your post I guess you want to extract the album name, i.e. the part before the minus sign.

Why not match against '(.*) - (.*)', being the first group the album and the second the title. The problem is with strings like "Album with minus - sign - First track" or "My Album - Track is one - two - three". But also as a human you wouldn't know there where the album ends and the track starts.