BASH: setting an environment variable from within my script doesn't set it anywhere else - how can I export globally? Simple example within

BASH: setting an environment variable from within my script doesn't set it
anywhere else - how can I export globally? Simple example within

PROMPT> pwd
/Users/jon/dev/test
PROMPT> ls -al
total 8
drwxr-xr-x 3 jon 102B Aug 27 21:34 ./
drwxr-xr-x 14 jon 476B Aug 27 21:33 ../
-rwxr-xr-x 1 jon 147B Aug 27 21:34 init*
PROMPT> cat init
#!/bin/sh
DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
export SCRIPT_HOME=${DIR%/bin}
echo "SCRIPT_HOME has been set to: $SCRIPT_HOME"
PROMPT> ./init
SCRIPT_HOME has been set to: /Users/jon/dev/test
PROMPT> echo $SCRIPT_HOME
PROMPT> why did that command not work?
-bash: why: command not found
PROMPT>