On 10/12/22 14:51, Paulo da Silva wrote:
Às 19:14 de 12/10/22, Jon Ribbens escreveu:
On 2022-10-12, Paulo da Silva <p_d_a_s_i_l_v_a...@nonetnoaddress.pt>
wrote:
Às 05:00 de 12/10/22, Paulo da Silva escreveu:
Hi!
The simple question: How do I find the full path of a shell command
(linux), i.e. how do I obtain the corresponding of, for example,
"type rm" in command line?
The reason:
I have python program that launches a detached rm. It works pretty well
until it is invoked by cron! I suspect that for cron we need to specify
the full path.
Of course I can hardcode /usr/bin/rm. But, is rm always in /usr/bin?
What about other commands?
Thank you all who have responded so far.
I think that the the suggestion of searching the PATH env seems the
best.
Another thing that I thought of is that of the 'which', but, to avoid
the mentioned recurrent problem of not knowing where 'which' is I would
use 'type' instead. 'type' is a bash (sh?) command.
If you're using subprocess.run / subprocess.Popen then the computer is
*already* searching PATH for you.
Yes, and it works out of cron.
Your problem must be that your cron
job is being run without PATH being set, perhaps you just need to edit
your crontab to set PATH to something sensible.
I could do that, but I am using /etc/cron.* for convenience.
Or just hard-code your
program to run '/bin/rm' explicitly, which should always work (unless
you're on Windows, of course!)
It can also be in /bin, at least.
A short idea is to just check /bin/rm and /usr/bin/rm, but I prefer
searching thru PATH env. It only needs to do that once.
I've read quite a bit of this thread without completely understanding
the actual problem.
Crontabs have always been good at exposing the problem of "is my program
expecting something to be set up which isn't guaranteed?" - usually
environment variables, of which PATH is one. "But it worked from my
login shell....".
Python's standard library has a tool for you:
shutil.which = which(cmd, mode=1, path=None)
Given a command, mode, and a PATH string, return the path which
conforms to the given mode on the PATH, or None if there is no such
file.
`mode` defaults to os.F_OK | os.X_OK. `path` defaults to the result
of os.environ.get("PATH"), or can be overridden with a custom search
path.
Since cron usually runs in a minimal environment, you should be able to
use this to supply a decent value for PATH, look up the command you
need, and then use that path to launch the command - or fail in some
sort of graceful way if not found, so you can hear about it and make
corrections.
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