envdefault

Set defaults for environment variables not already set.

Utility to run a POSIX shell script & report any variables set in that subshell that were not already set: this utility helps load environment variables that may have been missing, loads with priority lower than those already loaded.

Usage

envdefault expects either a single script to source, or, stdin which it will source. After sourcing the content in a subshell, it will print out (& source) all new variables exported.

Invoke as a program

export FOO=bar
echo export FOO=baz DOG=shibe > defaults
envdefault defaults

Would output export DOG=shibe.

After sourcing defaults (securely, inside a temporary subshell), envdefault finds:

1. The variable FOO had already been set, so it can be ignored.
2. The variable DOG is new, so print that value (and export it).

One can directly Source envdefault, but one can also imagine using envdefault via eval- eval $(envdefault defaults) as a namesake way to load environment variables at a low, "default" priority.

Stdin

Absent any arguments, envdefault accepts stdin as the source for it's subshell. The invoke example might become:

export FOO=bar
echo export FOO=baz DOG=shibe | envdefault

To output the same export DOG=shibe result. Again, FOO was already set so not reported, but DOG is new, so it's default is echoed.

Source

Alternatively, in a large variety of shells, one can source envdefault: echo export FOO=baz DOG=shibe > defaults ; . envdefault defaults.