How can I assign a value to an array in Bash? - arrays

Question

I am trying to read a list of values from a text file, hello.txt, and store them in an array.
counter=0
cat hello.txt | while read line; do
${Unix_Array[${counter}]}=$line;
let counter=counter+1;
echo $counter;
done
echo ${Unix_Array[0]}
echo ${Unix_Array[1]}
echo ${Unix_Array[2]}
I am not able to assign values to the array Unix_Array[]... The echo statement does not print the contents of the array.

Answer 1

There are a few syntax errors here, but the clear problem is that the assignments are happening, but you're in an implied subshell. By using a pipe, you've created a subshell for the entire while statement. When the while statement is done, the subshell exits and your Unix_Array ceases to exist.
In this case, the simplest fix is not to use a pipe:
counter=0
while read line; do
Unix_Array[$counter]=$line;
let counter=counter+1;
echo $counter;
done < hello.txt
echo ${Unix_Array[0]}
echo ${Unix_Array[1]}
echo ${Unix_Array[2]}
By the way, you don't really need the counter. An easier way to write this might be:
$ oIFS="$IFS" # Save the old input field separator
$ IFS=$'\n' # Set the IFS to a newline
$ some_array=($(<hello.txt)) # Splitting on newlines, assign the entire file to an array
$ echo "${some_array[2]}" # Get the third element of the array
c
$ echo "${#some_array[#]}" # Get the length of the array
4

Answer 2

If you are using Bash v4 or higher, you can use mapfile to accomplish this:
mapfile -t Unix_Array < hello.txt
Otherwise, this should work:
while read -r line; do
Unix_Array+=("$line")
done < hello.txt

Answer 3

The best way I found is:
declare -a JUPYTER_VENV
JUPYTER_VENV+=( "test1" "test2" "test3" )
And then consume it with:
for jupenv in "${JUPYTER_ENV[#]}"
do
echo "$jupenv"
done

Answer 4

Instead of this:
cat hello.txt | while read line; do
${Unix_Array[${counter}]}=$line;
let counter=counter+1;
echo $counter;
done
You can just do this:
Unix_Array=( `cat "hello.txt" `)

Answer 5

It’s a solution:
count=0
Unix_Array=($(cat hello.txt))
array_size=$(cat hello.txt | wc -l)
for ((count=0; count < array_size; count++))
do
echo ${Unix_Array[$count]}
done