Doesn't the ;?? mean match semi-colon 0 or 1 times and be non-greedy?

It does, but it only makes that part of the match non-greedy. The (.+) remains greedy.

But if you make that part non-greedy, then you will be asking to capture as little as possible following the ':', that might or might not be followed by a ';'. Which means it will capture just a single character.

A couple of ways to approach the problem:

1. Make capture non-greedy and have a definite terminating condition:/$some_variable\:(.+?)(?:;|$)/

   Where (?:;|$) requires a semicolon or the end-of-string, (prefering the former) to terminate the capture.

2. Or as you know the bit you want to capture cannot contain a ';', reduce the scope of the capture using [^;]+ in place of '.' and omit the terminator.

   /$some_variable\:([^;]+)/
   [download]

Either works:

$pet_list = 'dog:boston.terrier;cat:orange.tabby';;

$pets=[]; 
$pet_list =~ /$_\:(.+?)(?:;|$)/ and push @{$pets},$1 for qw[cat dog]; 
print for @{$pets};;
orange.tabby 
boston.terrier

$pets=[]; 
$pet_list =~ /$_\:([^;]+)/ and push @{$pets},$1 for qw[cat dog]; 
print for @{$pets};;
orange.tabby 
boston.terrier
[download]