python fabric multiple commands

Question

I'm trying to understand how fabric is working with multiple commands on one machine. I need to run several commands on each host (thousands of hosts) and would like to know what would be best.

Using multiple runs:

res_1 = run(command_1)
res_2 = run(command_2)
...
...
res_n = run(command_n)

Or:

res = run(command_1 && command_2 && ... command_n)
res.splitlines()
res_1 = res[0]
res_2 = res[1]
...
...
res_n = res[n-1]

What I want to know is how fabric handles multiple runs, will it open multiple sessions or do all commands in the same session?

e4c5 · Accepted Answer · 2017-06-05 14:35:34Z

5

Regardless of whether you use multiple run calls or a single run call with &&, AFAIK, fabric will open only one network connection. The difference between the two is that each new run executes in a different environment. For example you can try this.

run('ls')
run('cd /tmp/')
run('ls')

Both times it will show you a listing of your home directory. But if you try this

run('ls')
run('cd /tmp/ && ls')

It will show you your home directory the first time, followed by a listing of /tmp/. Thus if you want the state to be preserved from one command to another you should do run('cmd1 && cmd1') but if you are not bothered about it, you should use multiple run calls.

edited Jun 5, 2017 at 14:35

answered Jun 5, 2017 at 11:37

e4c5

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2 Comments

Amir Rossert Over a year ago

My commands are independent of each other so it is recommended to use multiple runs?

e4c5 Over a year ago

Yes, I would use multiple runs if nothing else. they are more readable.

Błotosmętek · Accepted Answer · 2017-06-05 08:13:30Z

1

The important difference between those two approaches is that the first one will run all commands regardless of the exit status of former commands; the second one, however, will only execute commmand_2 if command_1 returned no error, etc. So it is up to you if you want this behaviour or the other.

answered Jun 5, 2017 at 8:13

Błotosmętek

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3 Comments

e4c5 Over a year ago

Hang on a sec, unless I am very much mistaken, if any of the commands return non zero exit states, fabric will not run the rest regardless of whether you use style 1 or style 2

Błotosmętek Over a year ago

I stand corrected - unless warn_only is set to True, it will behave as you said.

Amir Rossert Over a year ago

What I'm trying to understand is if using multiple run will cause more "network overhead" then using one run to execute multiple commands

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