set values to output of a command

[rsgalloway]

Would be nice to support setting values to the output of a command, e.g.

PYVERSION: `python --version`

or

PYVERSION: $(python --version)

would set $PYVERSION to "Python 3.8.17"

[rsgalloway]

this could also be used in issue #17 for getting decryption keys from a secure key storage service like AWS SM:

KEY: $(aws secretsmanager get-secret-value --secret-id <SECRET_NAME>)

[rsgalloway]

technically this is partially supported now by piping the output of a command into --set:

$ echo "PYVERSION:`python --version`" | envstack --set -o py.env
$ ./py.env -r PYVERSION
PYVERSION=Python 3.8.10

another example:

$ echo "NOW:`date`" | envstack --set -o date.env
$ ./date.env -r NOW
NOW=Sun 24 Aug 2025 05:54:36 AM PDT

but this only works one time, it's not resolved dynamically every time the env is loaded.