source a shell-script, that means the current shell instance is reading the script line-by-line and executing the commands on the spot, as if you had entered them on the command-line (if you are executing the
source call from the prompt) or as if you had copy-and-pasted them into the script (if you are sourcing from a script).
Therefore, the different shell scripts
file-2.sh both behave as having a locally defined shell variable that only coincidentally has the same name
some_value in both cases. Even if you ran the two scripts in parallel, they would not know anything about each other, and so there are no cross-interactions between them - the sub-shell in which
file-1.sh is running does not know that the sub-shell in which
file-2.sh is running also happens to have a variable
As a side note, your attempt at creating an arithmetic expression as
will not have the effect you may imagine. For
file-1.sh it will yield
5+10 literally, and for
file-2.sh it will yield
10+10 literally. In order to perform arithmetic evaluation, you have to place it in an arithmetic expansion, as in
I would recommend checking shell-scripts with
shellcheck, also available as standalone tool on many Linux distributions, to catch syntax (and some logical) errors.