bash trouble assigning to an array index in a loop

Question

I can get this to work in ksh but not in bash which is really driving me nuts. Hopefully it is something obvious that I\'m overlooking.

I need to run an external com

Answer 1

Because your while loop is in a pipeline, all variable assignments in the loop body are local to the subshell in which the loop is executed. (I believe ksh does not run the command in a subshell, which is why you have the problem in bash.) Do this instead:

while read line
do
    array[i]="$line"
    echo "array[$i] = ${array[i]}"
    let i++
done < junk.txt

Rarely, if ever, do you want to use cat to pipe a single file to another command; use input redirection instead.

UPDATE: since you need to run from a command and not a file, another option (if available) is process substitution:

while read line; do
...
done < <( command args ... )

If process substitution is not available, you'll need to output to a temporary file and redirect input from that file.

If you are using bash 4.2 or later, you can execute these two commands before your loop, and the original pipe-into-the-loop will work, since the while loop is the last command in the pipeline.

set +m    # Turn off job control; it's probably already off in a non-interactive script
shopt -s lastpipe
cat junk.txt | while read line; do ...; done

UPDATE 2: Here is a loop-less solution based on user1596414's comment

array[0]=hello
IFS=$'\n' array+=( $(command) )

The output of your command is split into words based solely on newlines (so that each line is a separate word), and appends the resulting line-per-slot array to the original. This is very nice if you are only using the loop to build the array. It can also probably be modified to accomodate a small amount of per-line processing, vaguely similar to a Python list comprehension.