Close. You need to note the differences between "s and 's a little more carefully:)

I think this does what you want. Sometimes it helps to spread the individual clauses of a statement across seperate lines. It helps you keep track of what is going on. I've also added parens to the join function. They often aren't necessary, but it helps to clarify what bits are arguments to join and which bits (the return from join included) are arguments to print.

for (keys %probes) {
    print "$target_name :\n",  
          join( "\n", @{$probes{$_}} ),
          "\n";
}
[download]

HTH.