In Awk, are $_ and $0 synonyms?

Question

I find no reference to $_ in the Gnu Awk manual or the Wikipedia page, but I used it by mistake from a Perl habit and it seems to be identical to $0.

ping www.bbc.co.uk | awk '{print NR,$_}'
ping www.bbc.co.uk | awk '{print NR,$0}'

Is it some very old deprecated behaviour nobody's bothered to remove?

Answer 1

In OP's code:

ping www.bbc.co.uk | awk '{print NR,$_}'

Explanation: Above awk code its considering _ as a variable here, since no value is defined for variable _ so its value is zero(0) that's why it becomes from NR,$_ to NR,$0 and hence printing current line. So there is no special meaning for $_ unlike perl etc.

So even someone tries like: ping www.bbc.co.uk | awk '{print NR,$E}' also will print the samething.