Add default expansion.

[vantreeseba]

Allow expansion to occur, but replace non existing with default if
given.

fixes #11

Example: ${MACHINE-localhost}

Should resolve to $MACHINE expansion, and if not set, then expands to
localhost.

[vantreeseba]

There are a few more test conditions I'm adding to ensure no issues occur.

[vantreeseba]

This should be good to, let me know if there is anything else you feel like should be tested / etc.

[snyamathi]

Would using :- make more sense to mimic the shell syntax?

${parameter:-word}
Use Default Values. If parameter is unset or null, the expansion of word shall be substituted; otherwise, the value of parameter shall be substituted.

https://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_02

[vantreeseba]

Would using :- make more sense to mimic the shell syntax?

${parameter:-word}
Use Default Values. If parameter is unset or null, the expansion of word shall be substituted; otherwise, the value of parameter shall be substituted.

https://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_02

Yeah, that makes more sense, I guess I missed that somehow, and in bash (at least 4.4.20) it works without the ":", so ${non_existing-default} will return default.

I'll look into changing it.

[paulrostorp]

any updates on this ?

[vantreeseba]

Hey sorry, I honestly completely forgot about this, I will try to look into it this week.

[vantreeseba]

With those two latest commits, this should be good to go.
Tests all are passing, let me know if there is anything else you would like.

[elie-g]

Any updates?

[FezVrasta]

Anything holding back on this PR?

[motdotla]

Great feature. Thank you. Merging and this will be a major upgrade release shortly.

[motdotla]

Thank you 💛. This has been released: /~https://github.com/motdotla/dotenv-expand/blob/master/CHANGELOG.md#600-2022-01-17

[FezVrasta]

@vantreeseba may you help me understand how is this supposed to work? Why are UNDEFINED_ENV_KEY2 and ${UNDEFINED_ENV_KEY_3:-default} being concatenated?

Should ${MACHINE${MACHINE}} resolve to machinemachine?

This syntax doesn't seem to work on Bash, I get bad substitution. The correct one should be this I think:

UNDEFINED_EXPAND_WITH_DEFAULT_NESTED_TWICE=${UNDEFINED_ENV_KEY:-${UNDEFINED_ENV_KEY_2}${UNDEFINED_ENV_KEY_3:-default}}

[vantreeseba]

That actually looks like my test was missing a :-

So it should look like

UNDEFINED_EXPAND_WITH_DEFAULT_NESTED_TWICE=${UNDEFINED_ENV_KEY:-${UNDEFINED_ENV_KEY_2:-${UNDEFINED_ENV_KEY_3:-default}}}

Idea being, it's a n, n+1,n+2 test to do a "proof by induction".

I can fix it, or if you want to fix it in your branch is fine, whichever everyone thinks will be easier/better.

It passed due to the empty env vars being resolved to empty strings, so it probably should have more test cases like the previous defined/nested undefined ones.

[FezVrasta]

Fixed in my branch, thanks for confirming!