Nrthugu

I'm learning bash programming through a book and now I'm learning about opening files and file descriptors but I can't get this code to work(see below), I want to use the file descriptor 4 to write the output of the lower while loop to a file somefile24.log but somefile24.log is empty after I run the code.

Here is the code:

#!/bin/bash

#

# openFile.sh: print the contents of orders.txt



shopt -s -o nounset



declare LINE



exec 3< orders.txt

while read LINE <&3

do

    printf "%sn" "$LINE"

done





echo

echo "Here is the new part of the program!"





exec 4> somefile24.log

count=1

while read LINE <&3

do

    printf "%s-----count=%dn" "$LINE" "$count" >&4

    let count++

done

exit 0

Here is the output:

(something78@notemDEB78)-(01:45:03)-(~/Bash_Programming_2018)

$./openFile.sh 

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something

something and something and something



Here is the new part of the program!

Expected output is:

The script writes the contents of orders.txt to somefile24.log

I've tried to check the code in shellcheck but it doesn't see the problem and only gives me this:

$ shellcheck myscript



Line 10:

while read LINE <&3

      ^-- SC2162: read without -r will mangle backslashes.



Line 22:

while read LINE <&3

      ^-- SC2162: read without -r will mangle backslashes.



Line 25:

    let count++

    ^-- SC2219: Instead of 'let expr', prefer (( expr )) .

I've tried to make a test on the command line:

(something78@notemDEB78)-(01:59:41)-(~/Bash_Programming_2018)

$exec 3>somefile24.log 

(something78@notemDEB78)-(01:59:59)-(~/Bash_Programming_2018)

$echo testing >&3

(something78@notemDEB78)-(02:00:03)-(~/Bash_Programming_2018)

$cat somefile24.log 

testing

I know that I can just do:

while

printf "%sn" "$LINE" >> somefile24.log

QUESTION:

Is it possible to use a file descriptor to write to a file like this in a loop and if so how and what am I doing wrong?

And why is somefile24.log alway's empty after I run the script?

You already read the contents of the file in your first loop. Hence the file descriptor 3 is already at EOF. You can reset the file descriptor 3 before you read on it again. E.g. before your second loop, run this again exec 3< orders.txt

After the first loop the file descriptor is at EOF. So you need to reset the file descriptor before going in to the second loop.