如何在bash中为数组赋值？

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

Its 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