Shell Programming and Scripting

Thank you all so much for your quick replies! Both cfajohnson 's and devtakh's codes
did exactly what I was looking for.

I understand awk is a powerful tool to manipulate text files; if you could please recommend a good source for beginners that would be very appreciated; and/or if you could let me know what these two lines are doing, for the next time I have to deal with a similar problem... Thank you and have a great day!

awk -v num=$n '{ $(NF+1) = num; print }' "$file" > "$file.new"
n=$(( $n + 1 ))

Regina

Code:

awk -v num=$n '{ $(NF+1) = num; print }' "$file" > "$file.new"
n=$(( $n + 1 ))

So, the -v num=$n is making awk set the variable "num" to the value of $n (originally set to 1 before the loop). So the first time the loop runs, it sets num to 1.

Within the awk block, you see $(NF+1), NF is the "number of fields" in that record. So if it has 5 fields, then NF is 5. You can access a field by using $() and it will evaluate what is inside and then access that field, meaning that if you did $(NF) it would access the last field (NF being how many fields are in the record as stated before). So if you did $(NF+1) it would add 1 to the number of fields and access that field. So if you had 5 fields, it would access the 6th field. In this particular case the awk block is setting the last field+1 to the value of num (which is incremented with each iteration of the loop). It then prints the entire record (print is the same as print $0 which is to print the entire record).

"$file" > "$file.new" is reading from $file and writing to $file.new So it performs all of the actions on the content in $file but does not change it there, but instead writes all of the changes/modifications/etc to $file.new

The last part is n=$(( $n + 1 )), which just increments n by 1 (so it increases by 1 every time the loop is entered).

Well.. I hope thats enough information!

Yes this is fantastic. Thanks a million!

just do it inside awk

Code:

awk '{ print $0,n++ > "file.new"}' file

That increments the number for every line in one file, not once for each file in a set of files.

ah, thanks, my bad.

Code:

awk 'FNR==1{n++}{print $0,n> "file_new"}' file*