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

##</code><code>##

$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