BASH: How to ask user input and store it for the future?

Question

I want to store a user message in a bash program, and then display the message the next time the user runs the script.

One way I thought this might work is if I export the message to an environmental variable, but I cannot get it to work.

Here is what I have so far, but it is not working:

echo "Last message was: $KEEPTHISMESSAGE"
echo "Type the new message that you want to enter, followed by [ENTER]:"
read KEEPTHISMESSAGE
export KEEPTHISMESSAGE

What am I doing wrong? If there is a better way to do this, please let me know. Maybe keep a file that keeps a history of these message and gets the most recent?

Answer 1

You cannot use EXPORT this way. It only exports to processes started from within that invocation of the script. You must store the message in a file on the filesystem and load it in the next time your user executes the script. Very simply:

echo "Last message was: $(cat message.txt)"
echo "Type the new message that you want to enter, followed by [ENTER]:"
read KEEPTHISMESSAGE
echo $KEEPTHISMESSAGE > message.txt

You'll have to work out what happens the first time (when message.txt doesn't exist), and issues with relative/absolute paths to message.txt if you're running the script in a different directory.

Answer 2

Scripts can only directly export variables to their sub-processes. They can't export to parent processes.

You can alter a parents environment by invoking your script like this:

$ . /path/to/your_script.sh

Here your script should have an export statement to export the variable and must not have an exit statement.