How to merge two files in awk??

[Tom Christiansen]

>From the keyboard of @xlab1.uucp ():
: I am not sure if this question has been asked before...
:
: Supposing I have two files with three collumns in each. How do
: I merge the files and generate a single file with six or more 
: collumns using shell script?  for example if File A has collumns a, c, e 
: and File B has collumns b, d, f. I want to generate File C
: with collumns a,b,c,d,e,f.  Also it would be nice to be able to
: using the arithematic feature in awk...

This originally went also to comp.unix.internals.  I sure wouldn't
say an awk question is a unix internal.

Someone out there may have as paste solution, but I didn't see one.  

In old, standard awk, it's really quite cumbersome, as you have to read in
all the first file, then all the second file.  I find this to be a pretty
cumbersome solution.

    #!/bin/awk -f
    { a[NR] = $1; b[NR] = $2; c[NR] = $3; }
    END {
	count = NR/2;
	for (i = 1; i <= count; i++) {
	    print a[i], a[i+count], b[i], b[i+count], c[i], c[i+count];
	}
    }


In gawk (and nawk if you're rich), it's a little easier because you can
redirect getilne from a file, effectively reading two lines and writing
one line each iteration.  

    #!/usr/gnu/bin/gawk -f
    BEGIN {
	for (;;) {
	    if ((getline < ARGV[1]) <= 0) break;
	    a = $1; c = $2; e = $3;
	    if ((getline < ARGV[2]) <= 0) break;
	    b = $1; d = $2; f = $3;
	    print a, b, c, d, e, f;
	}
    }

It's also pretty easy in perl:

    #!/usr/bin/perl
    $[ = 1; $, = " "; $\ = "\n"; # awk emulation
    open(F1, $ARGV[1]); open(F2, $ARGV[2]);
    while ( (@a = split(' ',<F1>)) && (@b = split(' ', <F2>)) ) {
	print $a[1], $b[1], $a[2], $b[2], $a[3], $b[3];
    }

Other advantages of perl are:

    1) you get better error messages for syntax errors 
    2) you can symbolically debug your program
    3) no limits on lines/fields (gawk is better than nawk at this)
    4) can often be made to run faster than awk 
    5) better usage and i/o failure error messages (i didn't do this here)


If you only have awk and not gawk and perl, you should get them, because
they are both free and compile on a vast array (list? :-) of platforms.
Find them wherever GNUware is stored.

: Finally, how do u specify the "rest of the line" in awk??

I'm not really sure what you mean.  The whole line is $0.  What's the rest
of the line?  You mean fields past the third one?

--tom
--
"Hey, did you hear Stallman has replaced /vmunix with /vmunix.el?  Now
 he can finally have the whole O/S built-in to his editor like he
 always wanted!" --me (Tom Christiansen <tchrist at convex.com>)