Logging to stderr

[joshwlewis]

Unlike cli.action, the basic logging commands like cli.log, cli.info, cli.debug, cli.url only send text to stdout. There is no option to send these messages to stderr. Using stdout for these messages makes these utilities unusable for CLIs aiming to use stdout/stdin pipes.

For instance, when creating a pipeable command like oclif create-my-config | xargs cat, the only message that should go to stdout would be the filename. Any other informational or human messaging (such as 'Using default config') is better suited for stderr to prevent pipe corruption.

It would be nice to have an option to send informational messages to stderr instead. It might even make more sense to make stderr the default, and let stdout be a more intentional and explicit choice. Given that many CLIs around the unix ecosystem operate in this manner, we'd be in good company.

[mars]

make stderr the default

While this might be a breaking change for folks that have been forced to parse stdout for results of a command, it would ensure that stdout is clean, so that intentional command output is not mixed up with logs.

[jugglinmike]

Accepting a writable stream as input would be even better. That would allow folks to use not only process.stderr but also a stream of their own creation, which is much easier to observe in an automated testing environment.