Shell Programming and Scripting

awk '
FNR == 1 {
        # This is the 1st line in a file; increment file count.
        f++
}
{       # Collect data from input files.
        d[f, cnt[f] = FNR] = $0
}
END {   # Verify that number of lines in the 1st two files are identical...
        if(cnt[1] != cnt[2]) {
                print "1st two files do not have the same number of lines."
                exit 1
        }
        # Verify that we were given 3 input files...
        if(f != 3) {
                printf("Found %d files, expected 3.\n", f)
                exit 2
        }
        # For each set of values found in the 1st two files...
        for(i = 1; i <= cnt[1]; i++) {
                # Set output filename.
                of = "output" i
                # For each line in the 3rd file...
                for(j = 1; j <= cnt[3]; j++) {
                        # Initialize output line to data from the 3rd file.
                        o = d[3, j]
                        # Replace occurrences of hello1 and hello2 with data
                        # from the 1st and 2nd files, respectively.
                        gsub(/hello1/, d[1, i], o)
                        gsub(/hello2/, d[2, i], o)
                        # Write the modified line to the output file.
                        print o > of
                }
                # Close the current output file.
                close(of)
        }
}' hello[12].txt input