looping over different list files, retrieving always the sam Eline - list

Question

I have three files with a list of files I need to use later to apply a function.
I have managed to create a loop going through the 3 different files, but no exactly the output I need.
My input:
rw_sorted_test.txt
1
2
3
fwd_sorted_test.txt
A
B
C
run_list.txt
1st
2nd
3rd
I am running it like this:
for f in `cat rw_sorted_test.txt`; do for l in `cat fwd_sorted_test.txt`; do for r in `cat run_list.txt` do echo ${f} ${l} ${r}; done; done; done;
What I am obtain now is something like:
1 A 1st
1 A 2nd
1 A 3rd
2 A 1st
2 A 2nd
2 A 3rd
3 A 1st
(...)
What I am looking for is something like:
1 A 1st
2 B 2nd
3 C 3rd
I am sure that it will be something simple, but I am really beginner and all the workarounds have not been working.
Also, how can I then make it run after echo my desired output?
Thank you

Answer 1

Quick try, if it is this that you need:
exec 4< run_list.txt
exec 5< rw_sorted_test.txt
for a in $(cat fwd_sorted_test.txt); do
read run <&4
read sort <&5
echo "$sort $a $run"
done
...output is:
1 1st A
2 2nd B
3 3rd C
Files should also be closed:
exec 4<&-
exec 5<&-
The whole point is to do a single cycle, and read a line at a time from 3 different files. The files which are opened for input (exec ...< ...) should contain at least the same number of lines as the main file, which is controlling the loop.
Some reference could be find here: How do file descriptors work?
or doing some study on bash file descriptors. Hope it helps.

Answer 2

You can use this as a testcase for writing a program in awk:
3 inputfiles, store lines in an array and print everything in an END-block.
In this case you can use another program that works even easier:
paste -d" " rw_sorted_test.txt fwd_sorted_test.txt run_list.txt