Shell Programming and Scripting

a) You have to read lastline AND filename when you want to run the script on multiple files. This could be done in awk, reading results.txt as the first file and storing the lines in an array.
b) The influence on execution speed will be negligible (esp. doing it the way you proposed above) as awk still needs to read every single line just to count them...

what if we feed the last known number of lines of each file to awk. that way awk can begin reading that file from that point on.? i can do this in bash but it'll require a few lines of code...which i think will be inefficient.

Neither bash nor awk can do this because neither provides an interface to the lseek() system call. And, if either did, it would only be useful if all lines were of the same length, or if a byte count is saved instead of a line count.

dd can seek on a shared file descriptor on behalf of a subsequent process (such as awk), but that would only be useful when working with one file at a time.

Regards,
Alister