Defining codes/executables for ShellTask

[GeigerJ2]

For future reference:

src: ./statistics_foo
command: "./statistics.py"

with shebang, or, without:

src: ./statistics_foo
command: "python3 ./statistics.py"

with correct Python in the $PATH in the uenv.

• Also being able to provide the labels of already registered AiiDA Code instances?
• Possibly copy over directory ourselves before, rather than creating a PortableCode (@agoscinski).
• Make sure we don't create too many Code instances (e.g., automatically with aiida-shell), neither that we accidentally use the same Code for multiple tasks, where it shouldn't be used (e.g., because an instance is loaded from the DB)

[agoscinski]

Currently shell might not consider environments that are loaded in the prepend submission script to recover the executables.

plugin: shell
command: "python statistics.py"

We cannot support this for the moment since we do not load the load the environment in the prepend submission script where the executable is loaded and ShellJob cannot determine it with the which command So we rely on running python within a bash script. By default we use bash on remote (that one ShellJob finds with which since it is most likely not in an environment loaded) and if shebang is present in the script file (in the example above it would need to be used./statistics.py) we use it.

Discussion still ongoing. Open problem bash -l, does it mean we should just specify the command as it should be present in the submission script?