Why is fabric using /bin/sh

Question

I am trying to run some commands on a remote server. I need to source some bash files there. Unfortunately, it seems fabric has (suddenly, recently?) started using /bin/sh, and it breaks because I use bash syntax in my scripts. I have found this:

If shell is True (the default), run will execute the given command string via a shell interpreter, the value of which may be controlled by setting env.shell (defaulting to something similar to /bin/bash -l -c "".) Any double-quote (") or dollar-sign ($) characters in command will be automatically escaped when shell is True.

I have not changed env.shell, so I do not know why fabric starts using sh. In any case, I am overwriting it, but still no luck:

env.shell = "/bin/bash"

What could be causing this? What can I do to force fabric to use bash?

Answer 1

It took some digging, but this is what I found:

It is possible to see what fabric is doing behind the scenes:

from   fabric.api                                        import output

FAB_SHOW_RUNNING  = True   # Show the command that fabric runs
FAB_SHOW_STDOUT   = False  # Show the stdout of the command run
FAB_SHOW_STDERR   = False  # Show the stderr of the command run
FAB_SHOW_DEBUG    = True   # Increase logging detail for messages
FAB_SHOW_USER     = True
FAB_SHOW_STATUS   = False  # Prevent fabric from using print in some situations (at least in disconnect_all)
FAB_SHOW_WARNINGS = False  # Avoid fabric from showing messages about failed commands

output['running']  = FAB_SHOW_RUNNING
output['stdout']   = FAB_SHOW_STDOUT
output['stderr']   = FAB_SHOW_STDERR
output['debug']    = FAB_SHOW_DEBUG
output['user']     = FAB_SHOW_USER
output['status']   = FAB_SHOW_STATUS
output['warnings'] = FAB_SHOW_WARNINGS

It turned out it is not fabric using /bin/sh but, since I was (in this particular case) running local commands, the culprit was the subprocess module. In order to specify the shell to be used, you need to specify shell=True and executable='/bin/bash'