Re: [Libguestfs] Shebang sh plugins

On 11/23/19 9:46 AM, Richard W.M. Jones wrote: That is not portable; not all kernels permit more than one argument in #!. You can work around it with modern env (both BSD and Coreutils have recently added -S), as: #!/usr/bin/env -S nbdkit python which will then invoke the desired 'nbdkit' 'python' 'file' regardless of whether the OS invoked 'env' '-S nbdkit python' (Linux) or 'env' '-S' 'nbdkit' 'python' (others). But that in turn assumes env -S is portable (it's fairly new, so not yet). Otherwise, interpreted plugin shebangs really do have to hard-code the expected path of nbdkit rather than relying on env, unless we find a way to make: nbdkit file determine that when 'nbdkit-plugin-file.so' does not exist but 'file' does, then inspect file to determine if 'nbdkit-plugin-interpreter.so' exists based on the first line of file. Except that would mean the first line changes to: #!/usr/bin/env nbdkit which lacks the desired interpreter, so we'd still have to add something like documenting that if the first line of the #! contains 'nbdkit', then the second line is some form of magic comment that includes the substring 'PLUGIN=...' (we have to allow arbitrary slop as prefix or suffix after a plugin name, to allow the second line to be a comment or otherwise innocuous interpreted line in whatever desired target language), so we end up with: #!/usr/bin/env nbdkit # PLUGIN=python where the initial invocation of '/usr/bin/env' 'nbdkit' 'file' then passes on to '/path/to/nbdkit' 'file' which sees that 'file' is not a plugin, but does have magic, so it then retries as if invoked as '/path/to/nbdkit' 'python' 'file' -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org