Bash array value different inside while loop [duplicate]

Question

I have a pretty simple shell script that uses a while loop to read values from a file, place them into an array and then print the content of the array. It correctly displays the content of the array after each addition inside the while loop. The issue is when I view the content of the array outside of the loop the table appears to be empty.

Here is the content of the script:

ctr=0
arr=()
cat "alpha.txt" |\
while IFS="," read data
do
   arr+=("$data")
   echo "$ctr.data: $data"
   echo "array inside loop: ${arr[@]}"
   let "ctr=ctr+1"
done
echo
echo "+++++"
echo "array outside loop: ${arr[@]}"
echo
echo "${arr[1]}"
echo "${arr[2]}"

The content of alpha.txt:

aaa
bbb
ccc

The output from the program:

0.data: aaa
array inside loop: aaa
1.data: bbb
array inside loop: aaa bbb
2.data: ccc
array inside loop: aaa bbb ccc

+++++
array outside loop:

I can't understand why I can't display the array's content outside of the loop. Any advice would be appreciated.

Also see BashFAQ/024 (I set variables in a loop that's in a pipeline. Why do they disappear after the loop terminates? Or, why can't I pipe data to read?). — pjh
– pjh, Commented Nov 2, 2024 at 16:59
Shellcheck identifies several problems with the code, including the problem that causes the array contents to be lost outside of the loop. The report that it produces includes links to more information about the problems and how to fix them. It's a good idea to run Shellcheck on all new and modified shell code. — pjh
– pjh, Commented Nov 2, 2024 at 17:03

kaslmineer7999 · Accepted Answer · 2024-11-02 16:54:37Z

1

the following is the solution:

ctr=0
arr=()
while IFS="," read data
do
   arr+=("$data")
   echo "$ctr.data: $data"
   echo "array inside loop: ${arr[@]}"
   let "ctr=ctr+1"
done < "alpha.txt"
echo
echo "+++++"
echo "array outside loop: ${arr[@]}"
echo
echo "${arr[1]}"
echo "${arr[2]}"

and why that is the solution:

because of pipelines making subshells, which means variables made in pipelines will not be seen by the script

answered Nov 2, 2024 at 16:54

kaslmineer7999

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