How to use 'readarray' in bash to read lines from a file into a 2D array

Question

Let's say I have a text file 'demo.txt' who has a table in it like this:

1 2 3     4 5 6     7 8 9     

Now, I want to read each line separately using the 'readarray' command in bash, so I write:

readarray myarray < demo.txt    

The problem is that it doesn't work. If I try to print 'myarray' with:

echo $myarray 

I get:

1 2 3 

Also, if I write:

echo ${myarray[1]} 

I get:

4 5 6 

Instead of:

2 

as I expected. Why is that? How can accesses each line separately and in that line get access to each member?

Answer 1

This is the expected behavior. readarray will create an array where each element of the array is a line in the input.

If you want to see the whole array you need to use

echo "${myarray[@]}" 

as echo "$myarray will only output myarray[0], and ${myarray[1]} is the second line of the data.

What you are looking for is a two-dimensional array. See for instance this.

If you want an array with the content of the first line, you can do like this:

$ read -a arr < demo.txt  $ echo ${arr[0]} 1 $ echo ${arr[1]} 2 $ echo ${arr[2]} 3