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

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.

score 17 · Accepted Answer · edited Oct 25 '21 at 21:08

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

**+1**. Also, note that putting `IFS=$'\n' declare some_array=($( — ghoti, Nov 03 '14 at 20:15

score 9 · Answer 2 · edited Oct 25 '21 at 21:16

9

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

edited Oct 25 '21 at 21:16

Peter Mortensen

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answered Jun 18 '12 at 17:39

jordanm

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+1 for calling out mapfile. I always forget about the new shell features. – kojiro Jun 18 '12 at 17:42

Zioalex · Answer 3 · 2021-09-22T13:17:06.283

2

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

edited Sep 22 '21 at 13:17

answered Mar 29 '19 at 09:59

Zioalex

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2

I think you mean `declare -a`; the uppercase version declares an _assoclative_ array (Bash 4+). – tripleee Sep 20 '21 at 08:38

Jon Lin · Answer 4 · 2012-06-18T17:45:16.487

0

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" `)

edited Jun 18 '12 at 17:45

answered Jun 18 '12 at 17:34

Jon Lin

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Without reassigning `IFS`, this will create multiple elements for any line with a space in it. – kojiro Jun 18 '12 at 17:41

score 0 · Answer 5 · edited Oct 25 '21 at 21:19

0

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

edited Oct 25 '21 at 21:19

Peter Mortensen

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answered Jun 19 '12 at 01:24

Arthur Alves

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This suffers from the same problem as Jon Lin's solution, namely, that you have to set `IFS` to a newline or you'll split on *any* whitespace in `hello.txt`. – kojiro Jun 19 '12 at 12:14

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

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