That code is incorrect. Since it occurs within double-quotes, $1 is replaced by the shell with the value of its first positional parameter, before AWK ever sees it. If, instead, you want it to refer the first field in AWK, you need to quote it, \$1.

The only reason I can think of for why you're getting the expected result is that the shell's first positional parameter, $1, is empty, and so AWK is only seeing "{ print }". Since lines split on the comma are yielding one-field records, within AWK, in this specific case, "print" (equivalent to "print $0") is equivalent to "print $1", and hence everything seems okay.

If I'm correct, setting $1 in the shell to a non-null value not equal to a literal '$0' or a literal '$1' will break the code.

Regards,
Alister

---------- Post updated 05-21-10 at 12:19 AM ---------- Previous update was 05-20-10 at 10:01 PM ----------

That output is incorrect. If you take a close look at the desired output that you provided, they are incorrectly sorted. The easiest to spot is "H:A,B,C,F". H occurs with F twice, and the others once. That line should be, "H:F,A,B,C". As a matter of fact, with the exception of the C and D lines, they are all wrong. A quick look at your code suggests that the problem lies in:

Specifically, 'for (i in arr)' is not guaranteed to return the array elements in any specific order. That pipeline sorts with the sort command but then that order is disgarded when the "in" operator is used.

Regards,
Alister