Is Awk and multiple file processing possible?

Question

I need to process two file contents. I was wondering if we can pull it off using a single nawk statement.

File A contents:

AAAAAAAAAAAA  1
BBBBBBBBBBBB  2
CCCCCCCCCCCC  3

File B contents:

XXXXXXXXXXX  3
YYYYYYYYYYY  2
ZZZZZZZZZZZ  1

I would like to compare if $2 (2nd field ) in file A is the reverse of $2 in file B. I was wondering how to write rules in nawk for multi-file processing ? How would we distinguish A's $2 from B's $2

EDIT: I need to compare $2 of A's first line (which is 1) with the $2 of B's last line (which is 1 again) .Then compare $2 of line 2 in A with $2 in NR-1 th line of B. And so on.....

Answer 1

You can do something like this -

[jaypal:~/Temp] cat f1
AAAAAAAAAAAA  1
BBBBBBBBBBBB  2
CCCCCCCCCCCC  3
DDDDDDDDDDDD  4

[jaypal:~/Temp] cat f2
AAAAAAAAAAA  5
XXXXXXXXXXX  3
YYYYYYYYYYY  2
ZZZZZZZZZZZ  1

Solution:

awk '
NR==FNR {a[i++]=$2; next}
{print (a[--i] == $2 ? "Match " $2 FS a[i] : "Do not match " $2 FS a[i])}' FileB FileA
Match 1 1
Match 2 2
Match 3 3
Do not match 4 5

Answer 2

You can make awk process files serially, but you can't easily make it process two files in parallel. You probably can achieve the effect with careful use of getline but 'careful' is the operative term.

I think in this case, with simple two-column files, I'd be inclined to use:

paste "File A" "File B" |
awk '{ process fields $1, $2 from File A and fields $3, $4 from file B }'

You would need to make sure the two files are in the appropriate order, etc.

If your input is more complex, then this may not work so well, though you can choose the character that separates the data from the two files with paste -d'|' ... to use a pipe to separate the two records, and awk -F'|' '{ ... }' to read $1 as the info from File A and $2 as the info from File B.