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.
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.
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:
- The variable FOO had already been set, so it can be ignored.
- 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.
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.
Alternatively, in a large variety of shells, one can source envdefault: echo export FOO=baz DOG=shibe > defaults ; . envdefault defaults.