Variables value gets lost in subshell

Question

This bash script concatenates the names for jar files to a classpath (variable CP), in the while loop the value is correct but is lost in the subshell as descibed in this related question Bash variable scope

#!/bin/bash
CP="AAA"
func() {
        ls -1 | while read JAR
        do
                if [ ! -z "$CP" ]; then
                        CP=${CP}':'
                fi
                CP=${CP}${JAR}
        done
        echo $CP # <-- prints AAA
}

func

My question is, since I can't figure out which element will be the last one, how can the value be saved.

Do I actually have to save the current value (repeatedly in the loop) to a file?

EDIT:

A colleague came up with this command sequence which works well

ls | xargs echo|tr ' ' :

Solution

The issue here is that using while in a pipeline creates a subshell, and a subshell cannot affect its parent. You can get around this in a few ways. For what you are doing now, this will suffice:

for JAR in *; do
    # Your stuff
done

Another thing to note is that you shouldn't rely on parsing ls

This also shows you ways to avoid the subshell.