This came up a little in another thread. Can someone explain some why awk (I happen to use gawk) behaves as follows:

Code:

$ cat file
aaa

Code:

$ awk 'BEGIN {print x}' x=1
[Blank line]

Code:

$ awk x=1 'BEGIN {print x}'
awk: fatal: cannot open file `BEGIN {print x}' for reading (No such file or directory)

Code:

$ awk -v x=1 'BEGIN {print x}'
1

Code:

$ awk 'BEGIN {print x} {print x}' x=1 file

1

Code:

$ awk 'BEGIN {print x} {print x}' file x=1
[Blank line]
[Blank line]

Code:

$ awk -v x=1 'BEGIN {print x} {print x}' file
1
1

Code:

$ awk -v x=1 'BEGIN {print x} {print x}' file x=2
1
1

Code:

$ awk -v x=1 'BEGIN {print x} {print x}' x=2 file
1
2

I understand this is "how it is". And it is clear to me what is happening. I'm interested in knowing "why". Any practical example to show the advantage or benefit of why it's set up like this?

The gawk man page says:
That's a little helpful, but not much. And I have not previously used "multiple passes", so maybe I'm missing something there.