# sort things containing a colon after things without

# fist attempt
if ( $a =~ /:/ ){
  return $a cmp $b if $b =~ /:/;
  return 1;
}
if ( $b =~ /:/ ){
  return -1;
}
$a cmp $b;

# version 2, only one $a cmp $b 
return  1 if ( $a =~ /:/ and $b !~ /:/ );
return -1 if ( $b =~ /:/ and $a !~ /:/ );
$a cmp $b;

# version 3 with input from a colleague, only apply a re to
# each var once now
if ( my $x = ($a =~ /:/) <=> ($b =~ /:/) ){ 
  return $x; 
}
$a cmp $b;

# maybe better maybe not but it allowed me to see the 
# final option-
my $x = ($a =~ /:/) <=> ($b =~ /:/);
$x ? $x : $a cmp $b;

# a good nights sleep and...
(($a =~ /:/) <=> ($b =~ /:/)) || $a cmp $b;