Second time: Trying to make a script prompt the user to enter a variable for the first time they run the script

Question

Trying to get bash to combine read and sed to insert a variable into a script. Doesn't necessarily have to be sed but something along those lines.

Something like so:

INTERNAL="`read -p "PATH " path` | sed -i '3i\$INTERNAL="/run/media/blah" blah.sh

I could also implement python as well. My project is written in shell but I could use a setup.py script for the initial run.

I'm trying to make a smart script to setup variables during the first run and save them for future usage. In this case it's a path to an external/internal device to backup $HOME. I am going to make the script search for a file: $HOME/.already_ran.txt(hidden dummy file for the script to search for to see if it's been ran before) If it doesn't find that file, it will prompt the user to enter the variables, in this case the paths. I don't want to have them have to open up the script manually and add the variable.

Answer 1

#!/bin/bash

conffile=$HOME/.myscript.env

if [[ -f $conffile ]]; then
    if ! source "$conffile"; then
        printf 'Error parsing configuration file "%s"\n' "$conffile"
        exit 1
    fi
else
    read -p 'Please enter device path: ' devpath

    # further steps to verify correctness of $devpath here
    # then...

    declare -p devpath >"$conffile"
fi

# the rest of the script using "$devpath" goes here

declare -p varname will output a bash statement that defines the variable varname with its current value. Writing this to a file gives you a file that you can source to recreate the variable.

For a simple shell variable, devpath, containing some pathname, /some/path, what is written to $conffile might be something like

declare -- devpath="/some/path"

The if-statement wrapping the source command ensures that if someone has tampered with the syntax of the saved file to make the shell unable to read it, the script will terminate.

declare -p may also be used to save environment variables and array variables etc. to file for later reconstruction.