Can I read line from a heredoc in bash?

Question

Here's what I'm trying. What I want is the last echo to say "one two three four test1..." as it loops. It's not working; read line is coming up empty. Is there something subtle here or is this just not going to work?

array=( one two three )
echo ${array[@]}
#one two three
array=( ${array[@]} four )
echo ${array[@]}
#one two three four


while read line; do
        array=( ${array[@]} $line )
        echo ${array[@]}
done < <( echo <<EOM
test1
test2
test3
test4
EOM
)

Answer 1

I would normally write:

while read line
do
    array=( ${array[@]} $line )
    echo ${array[@]}
done <<EOM
test1
test2
test3
test4
EOM

Or, even more likely:

cat <<EOF |
test1
test2
test3
test4
EOF

while read line
do
    array=( ${array[@]} $line )
    echo ${array[@]}
done

(Note that the version with a pipe will not necessarily be suitable in Bash. The Bourne shell would run the while loop in the current shell, but Bash runs it in a subshell — at least by default. In the Bourne shell, the assignments made in the loop would be available in the main shell after the loop; in Bash, they are not. The first version always sets the array variable so it is available for use after the loop.)

You could also use:

array+=( $line )

to add to the array.

Answer 2

replace

done < <( echo <<EOM

with

done < <(cat << EOM

Worked for me.

Answer 3

You can put the command in front of while instead:

(echo <<EOM
test1
test2
test3
test4
EOM
) | while read line; do
        array=( ${array[@]} $line )
        echo ${array[@]}
done