That code returns "We have a match". Although I'm think you hould use \Q and \E in comparison to avoid troubles with other strings.
So the code should look like this:

$line='123: ABC/1.0/VAL 111:222:333:444';
$cont='ABC/1.0/VAL 111:222:333:444';
if ($line=~/\Q$cont\E/) 
{ 
  print "We have a match\n"; 
} 
else 
{ 
    print "No match\n"; 
}
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