How do I source_once in bash?

Question

What's a good way of sourcing in just once in bash.

Does bash store the paths of the files that have been sourced in or do I need to make all source/. invocations go through a wrapper that will store those paths?

Is there a standardly available mechanism that will find what a source argument resolves to? which doesn't seem to work unless the file is executable.

Answer 1

In each of your files that you might source, add a statement. Suppose that the file /etc/interface is one of the files that you want to only source once, then format that file as follows:

if [ ! "$ETC_INTERFACE" ]
then
    # statements that you
    # want to source...
fi
export ETC_INTERFACE=Yes

This assures that the statements in /etc/interface are only executed once. If a script tries to source it again, it will see that ETC_INTERFACE has been set and skip the body of the file.

Alternate Approach

Suppose that one does not want to modify the files that are to be sourced but it is OK to modify the scripts which source them. In that case, source them as follows:

[ ! "$ETC_INTERFACE" ] && source /etc/interface && export ETC_INTERFACE=Yes