Re: [Libguestfs] Shebang sh plugins (was: Re: [PATCH nbdkit v2 03/10] python: Implement nbdkit API version 2.)

On Fri, Nov 22, 2019 at 02:55:31PM -0600, Eric Blake wrote: > Unrelated side topic: in your recent addition of eval.sh, you > wondered if we should promote it to a full-blown plugin rather than > just an example script. But reading 'man nbdkit-sh-plugin', there > is no mention of turning an executable script into a full-blown > plugin via a shebang, the way that python documents it. [I guess > 'man nbdkit' sort of mentions it under Shebang scripts] I believe it's not possible to do it for sh plugins. For (eg) python plugins it works like this: #!/usr/sbin/nbdkit python -> runs nbdkit python <script name> -> <script name> is interpreted as magic script= parameter -> the python plugin works by loading the script using PyRun_SimpleFileEx which interprets the contents of the script as python code However for shell it doesn't work: #!/usr/sbin/nbdkit sh -> runs nbdkit sh <script name> -> <script name> is interpreted as magic script= parameter -> the sh plugin works by actually executing the script -> executing the script repeats the steps over from the top, causing an infinite loop If you can think of a way to make this work it would be a useful feature IMO.