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?

Thanks for any comments/responses.
Paulo

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Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in
the PATH environment variable.

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On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in
the PATH environment variable.

erm, or try 'which rm' ?

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Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in
the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have
the same difficulty in using 'which' command. Do not you think?

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Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in
the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have
the same difficulty in using 'which' command. Do not you think?

--- SoupGate-Win32 v1.05
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Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in
the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have
the same difficulty in using 'which' Command. Do not you think?

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Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> writes:

(linux), i.e. how do I obtain the corresponding of, for example,
"type rm" in command line?

import os
import pathlib

paths = os.getenv( "PATH" )
for p in paths.split( os.pathsep ):
path = pathlib.Path( p ).joinpath( 'rm' )
try:
if path.exists(): print( path )
except PermissionError:
pass

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Sorry for the repetitions. Today I have network problems.

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jak <nospam@please.ty> wrote:

Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in >> the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have
the same difficulty in using 'which' command. Do not you think?

From a command prompt use the bash built-in 'command' :-

command -v rm

... and rm will just about always be in /usr/bin.

--
Chris Green
·

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Il 12/10/2022 14:20, Chris Green ha scritto:

jak <nospam@please.ty> wrote:

Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in >>>> the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have
the same difficulty in using 'which' command. Do not you think?

From a command prompt use the bash built-in 'command' :-

command -v rm

... and rm will just about always be in /usr/bin.

ok but I didn't suggest a very complicated thing:

for p in os.getenv('PATH').split(os.path.pathsep):
if p:
if os.path.isfile(os.path.join(p, 'rm')):
print(f)

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On 12/10/2022 07.20, Chris Green wrote:

jak <nospam@please.ty> wrote:

Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

I'm afraid you will have to look for the command in every path listed in >>>> the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have
the same difficulty in using 'which' command. Do not you think?

From a command prompt use the bash built-in 'command' :-

command -v rm

... and rm will just about always be in /usr/bin.

On two different versions of Ubuntu, it's in /bin.

--
Michael F. Stemper
Psalm 94:3-6

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On 2022-10-12, Michael F. Stemper <michael.stemper@gmail.com> wrote:

On 12/10/2022 07.20, Chris Green wrote:

... and rm will just about always be in /usr/bin.

On two different versions of Ubuntu, it's in /bin.

It will almost always be in /bin in any Unix or Unix-like system,
because it's one of the fundamental utilities that may be vital in
fixing the system when it's booted in single-user mode and /usr may
not be available. Also, the Filesystem Hierarchy Standard *requires*
it to be in /bin.

Having said that, nothing requires it not to be elsewhere *as well*,
and in Ubuntu and other Linux systems it is in /usr/bin too. And because
PATH for non-root users will usually contain /usr/bin before /bin (or
indeed may not contain /bin at all), 'command -v rm' or 'which rm' will
usually list the version of rm that is in /usr/bin.

e.g. on Amazon Linux:

$ which rm
/usr/bin/rm
$ sudo which rm
/bin/rm

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Michael F. Stemper <michael.stemper@gmail.com> wrote:

On 12/10/2022 07.20, Chris Green wrote:

jak <nospam@please.ty> wrote:

Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

I'm afraid you will have to look for the command in every path listed in >>>> the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have >> the same difficulty in using 'which' command. Do not you think?

From a command prompt use the bash built-in 'command' :-

command -v rm

... and rm will just about always be in /usr/bin.

On two different versions of Ubuntu, it's in /bin.

I think you'll find it's in both /bin and /usr/bin, usually /usr/bin
is earlier in the path so /usr/bin/rm is the one that will normally be
found first.

It's only in /bin/rm in case one has a system which mounts /bin
separately and earlier in the boot sequence and rm is one of the
commands needed early on.

--
Chris Green
·

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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.

Thanks
Paulo

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Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> schrieb:

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.

Probably you could use os.unlink[1] with no problem.

[1] <https://docs.python.org/3/library/os.html#os.unlink>

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Às 17:22 de 12/10/22, Tilmann Hentze escreveu:

Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> schrieb:

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.

Probably you could use os.unlink[1] with no problem.

No, because I need to launch several rm's that keep running after the
script ends.

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Jon Ribbens <jon+usenet@unequivocal.eu> writes:

On 2022-10-12, Michael F. Stemper <michael.stemper@gmail.com> wrote:

On 12/10/2022 07.20, Chris Green wrote:

... and rm will just about always be in /usr/bin.

On two different versions of Ubuntu, it's in /bin.

It will almost always be in /bin in any Unix or Unix-like system,
because it's one of the fundamental utilities that may be vital in
fixing the system when it's booted in single-user mode and /usr may
not be available. Also, the Filesystem Hierarchy Standard *requires*
it to be in /bin.

Having said that, nothing requires it not to be elsewhere *as well*,
and in Ubuntu and other Linux systems it is in /usr/bin too. And because
PATH for non-root users will usually contain /usr/bin before /bin (or
indeed may not contain /bin at all), 'command -v rm' or 'which rm' will usually list the version of rm that is in /usr/bin.

e.g. on Amazon Linux:

$ which rm
/usr/bin/rm
$ sudo which rm
/bin/rm

Have some major Linux distributions not done usrmerge yet? For any that
have, /bin is a symbolic link to /usr/bin

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On 2022-10-12, Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:

Jon Ribbens <jon+usenet@unequivocal.eu> writes:

On 2022-10-12, Michael F. Stemper <michael.stemper@gmail.com> wrote:

On 12/10/2022 07.20, Chris Green wrote:

... and rm will just about always be in /usr/bin.

On two different versions of Ubuntu, it's in /bin.

It will almost always be in /bin in any Unix or Unix-like system,
because it's one of the fundamental utilities that may be vital in
fixing the system when it's booted in single-user mode and /usr may
not be available. Also, the Filesystem Hierarchy Standard *requires*
it to be in /bin.

Having said that, nothing requires it not to be elsewhere *as well*,
and in Ubuntu and other Linux systems it is in /usr/bin too. And because
PATH for non-root users will usually contain /usr/bin before /bin (or
indeed may not contain /bin at all), 'command -v rm' or 'which rm' will
usually list the version of rm that is in /usr/bin.

e.g. on Amazon Linux:

$ which rm
/usr/bin/rm
$ sudo which rm
/bin/rm

Have some major Linux distributions not done usrmerge yet? For any that have, /bin is a symbolic link to /usr/bin

I have immediate access to CentOS 7, Ubuntu 20, and Amazon Linux 2,
and none of those have done that.

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On 2022-10-12, Paulo da Silva <p_d_a_s_i_l_v_a_ns@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. 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. Or just hard-code your
program to run '/bin/rm' explicitly, which should always work (unless
you're on Windows, of course!)

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On Wednesday, October 12, 2022 at 12:07:36 PM UTC+1, jak wrote:

Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in >> the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have
the same difficulty in using 'which' Command. Do not you think?

I don't need to know where the rm command is in order to use the which command.

I *was* (knowingly and deliberately) assuming that you have a semi-reasonably working system, and that your question meant "given command X, how do I
find where the executable X is on my system?".

Sounds like you want to make less assumptions than that. Fine. but probably best to be clear about your assumptions up front.

J^n

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On 2022-10-12 06:11, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in
the PATH environment variable.

Isn't that what the "whereis" command does?

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Op 12/10/2022 om 18:49 schreef Paulo da Silva:

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.

I fear that won't work.

If it doesn't work in cron, that probably means, PATH is not set
properly in your cron environment. And if PATH is not set properly,
searching it explicitely won't work either.

If rm works when evoked directly in a cron script but not via a python
script, you may need to export the PATH in your cron script.

--
Antoon Pardon

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On 2022-10-12 at 17:43:18 +0100,
Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

Às 17:22 de 12/10/22, Tilmann Hentze escreveu:

Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> schrieb:

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.

Probably you could use os.unlink[1] with no problem.

No, because I need to launch several rm's that keep running after the script ends.

rm doesn't take that long. Why are you detaching them?

(I'm not debating your point about cron.)

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Às 20:16 de 12/10/22, 2QdxY4RzWzUUiLuE@potatochowder.com escreveu:

On 2022-10-12 at 17:43:18 +0100,
Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

Às 17:22 de 12/10/22, Tilmann Hentze escreveu:

Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> schrieb:

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.

Probably you could use os.unlink[1] with no problem.

No, because I need to launch several rm's that keep running after the script >> ends.

rm doesn't take that long. Why are you detaching them?

Because the use of "rm -rf" here is to remove full dirs, mostly in
external drives, each reaching more than hundreds thousand files.

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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_ns@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.

--- SoupGate-Win32 v1.05
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On 2022-10-12, Jon Ribbens <jon+usenet@unequivocal.eu> wrote:

On 2022-10-12, Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:

Jon Ribbens <jon+usenet@unequivocal.eu> writes:

On 2022-10-12, Michael F. Stemper <michael.stemper@gmail.com> wrote:

On 12/10/2022 07.20, Chris Green wrote:

... and rm will just about always be in /usr/bin.

On two different versions of Ubuntu, it's in /bin.

It will almost always be in /bin in any Unix or Unix-like system,
because it's one of the fundamental utilities that may be vital in
fixing the system when it's booted in single-user mode and /usr may
not be available. Also, the Filesystem Hierarchy Standard *requires*
it to be in /bin.

Having said that, nothing requires it not to be elsewhere *as well*,
and in Ubuntu and other Linux systems it is in /usr/bin too. And because >>> PATH for non-root users will usually contain /usr/bin before /bin (or
indeed may not contain /bin at all), 'command -v rm' or 'which rm' will
usually list the version of rm that is in /usr/bin.

e.g. on Amazon Linux:

$ which rm
/usr/bin/rm
$ sudo which rm
/bin/rm

Have some major Linux distributions not done usrmerge yet? For any that
have, /bin is a symbolic link to /usr/bin

I have immediate access to CentOS 7, Ubuntu 20, and Amazon Linux 2,
and none of those have done that.

Sorry, in fact they have done that - I misread your comment as being
that they had symlinked the executables not the directories. This seems
quite an unwise move to me but presumably they've thought it through.

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Às 20:09 de 12/10/22, Antoon Pardon escreveu:

Op 12/10/2022 om 18:49 schreef Paulo da Silva:

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.

I fear that won't work.

If it doesn't work in cron, that probably means, PATH is not set
properly in your cron environment. And if PATH is not set properly,
searching it explicitely won't work either.

It seems you are right :-( I didn't think of that!
Does 'type' bash command work? I don't know how bash 'type' works.
I need to do some tests.
Thanks
Paulo

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On 2022-10-12, 2QdxY4RzWzUUiLuE@potatochowder.com <2QdxY4RzWzUUiLuE@potatochowder.com> wrote:

On 2022-10-12 at 17:43:18 +0100, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

Probably you could use os.unlink[1] with no problem.

No, because I need to launch several rm's that keep running after the script >> ends.

rm doesn't take that long.

Recursive ones can take a long time.

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Il 12/10/2022 20:19, MRAB ha scritto:

On 2022-10-12 06:11, jak wrote:

Il 12/10/2022 06:00, Paulo da Silva ha scritto:

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?

Thanks for any comments/responses.
Paulo

I'm afraid you will have to look for the command in every path listed in
the PATH environment variable.

Isn't that what the "whereis" command does?

"whereis" does more than the OP wants. A suitable command could be
"which" but if the OP is in a context where he needs to know the path
of the command, then it will have the same problem with "whereis" or
"which". In any case they would be a few lines of Python:

import os

def which(c):
for p in os.getenv('PATH').split(os.path.pathsep):
if p and os.path.isfile(f := os.path.join(p, c)):
return f
return ''

cmd = 'explorer.exe'
cmdp = which(cmd)

if cmdp:
print("found:", cmdp)
else:
print("not found"

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On 2022-10-12, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> 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_ns@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.

I assume you mean /usr/bin. But it doesn't matter. As already
discussed, even if 'rm' is in /usr/bin, it will be in /bin as well
(or /usr/bin and /bin will be symlinks to the same place).

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 cannot think of any situation in which that will help you. But if for
some reason you really want to do that, you can use the shutil.which()
function from the standard library:

>>> import shutil
>>> shutil.which('rm')
'/usr/bin/rm'

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Some thoughts / notes:
1. On our Ubuntu-Server 20.04.3 based systems, /bin/rm and /usr/bin/rm are hard links to the same file.

2. Put the following in a bash script and run it from cron. Then you can see what your environment is. Mine has PATH=/usr/bin:/bin in it.

#!/bin/bash
env > /tmp/env$$

3. You can background Python just as well as you can a separate rm invocation. if os.fork() == 0:
os.unlink(….)








From: Python-list <python-list-bounces+gweatherby=uchc.edu@python.org> on behalf of Grant Edwards <grant.b.edwards@gmail.com>
Date: Wednesday, October 12, 2022 at 5:03 PM
To: python-list@python.org <python-list@python.org>
Subject: Re: Find the path of a shell command
*** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. ***

On 2022-10-12, 2QdxY4RzWzUUiLuE@potatochowder.com <2QdxY4RzWzUUiLuE@potatochowder.com> wrote:

On 2022-10-12 at 17:43:18 +0100, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

Probably you could use os.unlink[1] with no problem.

No, because I need to launch several rm's that keep running after the script >> ends.

rm doesn't take that long.

Recursive ones can take a long time.

-- https://urldefense.com/v3/__https://mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!ny8-fSGJEE3wk-Yq188xuT5aamgIUVI6SJQHkNaxMp11JelflHEJ2SQcYqqSC1s8pxkifVVdFyeEcbSv1ZJlqoaxuG_m$<https://urldefense.com/v3/__https:/mail.python.org/mailman/
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On 2022-10-12, Jon Ribbens <jon+usenet@unequivocal.eu> wrote:

On 2022-10-12, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> 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_ns@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.

I assume you mean /usr/bin. But it doesn't matter. As already
discussed, even if 'rm' is in /usr/bin, it will be in /bin as well
(or /usr/bin and /bin will be symlinks to the same place).

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 cannot think of any situation in which that will help you. But if for
some reason you really want to do that, you can use the shutil.which() function from the standard library:

>>> import shutil
>>> shutil.which('rm')
'/usr/bin/rm'

Actually if I'm mentioning shutil I should probably mention
shutil.rmtree() as well, which does the same as 'rm -r', without
needing to find or run any other executables.

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On 10/12/2022 12:00 AM, Paulo da Silva wrote:

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?

Thanks for any comments/responses.
Paulo

Python has a command that usually does the job:

import shutil, os
executable_path = shutil.which(exename, os.X_OK)

If you know that the executable you want is on some non-standard path,
you can or them together:

executable_path = shutil.which(exename, os.X_OK)\
or shutil.which(exename, os.X_OK, other_path)

Presumably the shutil command uses which behind the scenes, but that
doesn't matter.

Now you can include this location when you run the executable from
Python. If you need to run a system command from a batch file and not
from Python, you will either need to have the right path in effect when
the batch file is run, or manually include the full path to the file in
the batch file.

BTW, on Linux Mint, which is derived from Ubuntu and Debian, rm is at

$ which rm
/bin/rm

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On 12Oct2022 17:49, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

Às 05:00 de 12/10/22, Paulo da Silva escreveu:
I think that the the suggestion of searching the PATH env seems the
best.

I just want to note that you want to not just check for existence of the
path, but that it is executable (permissionwise). You want to use `X_OK`
with the `os.access` function: https://docs.python.org/3/library/os.html#os.access

Also notice that the `shutil` module has a `which()` function: https://docs.python.org/3/library/shutil.html#shutil.which

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.

`which` will almost always be in `/usr/bin` (or `/bin` on some systems I suppose). But do you need to know where `which` is? If you're invoking
it instead of search `$PATH`, the normal executtion stuff itself search `$PATH`, an will find `which` for you :-)

'type' is a bash (sh?) command.

Yeah. Bash, ksh etc have `type`. It is a builtin, shich can see if a
command word you give it is a shell alias or function or builtin or
externally executed command. As you'd imagine, an external executable
like `which` has no access to the internals of your shell, and can only
look for executables.

Cheers,
Cameron Simpson <cs@cskk.id.au>

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On 12Oct2022 15:16, Dan Sommers <2QdxY4RzWzUUiLuE@potatochowder.com> wrote:

rm doesn't take that long. Why are you detaching them?

For big things it takes quite a while. On slow discs it can take quite a
while. For directory trees with many files it can take quite a while.
For remove filesystems, even a local to your LAN NAS, it can take quite
a while.

Certainly I've got real world modern day things right now where "quite a
while" can be many minutes.

I've got an `rmr` script of my own whose entire function is to rename
the target to something like `.frm.blah` and then remove `.frm.blah` in
the background. I use it a _lot_.

Ancient anecdote. We got funky new workstations at Uni long ago. For the
first time in my life "rm filename" came back to the command prompt with
no perceptable delay. So fast that I first wondered if it had worked at
all. Previously we'd been using shared minicomputers (PDPs, Vaxen).

Cheers,
Cameron Simpson <cs@cskk.id.au>

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Às 22:38 de 12/10/22, Jon Ribbens escreveu:

On 2022-10-12, Jon Ribbens <jon+usenet@unequivocal.eu> wrote:

On 2022-10-12, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> 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_ns@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.

I assume you mean /usr/bin. But it doesn't matter. As already
discussed, even if 'rm' is in /usr/bin, it will be in /bin as well
(or /usr/bin and /bin will be symlinks to the same place).

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 cannot think of any situation in which that will help you. But if for
some reason you really want to do that, you can use the shutil.which()
function from the standard library:

>>> import shutil
>>> shutil.which('rm')
'/usr/bin/rm'

Actually if I'm mentioning shutil I should probably mention
shutil.rmtree() as well, which does the same as 'rm -r', without
needing to find or run any other executables.

Except that you can't have parallel tasks, at least in an easy way.
Using Popen I just launch rm's and end the script.

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On 13Oct2022 08:50, Cameron Simpson <cs@cskk.id.au> wrote:

On 12Oct2022 15:16, Dan Sommers <2QdxY4RzWzUUiLuE@potatochowder.com> wrote: >>rm doesn't take that long. Why are you detaching them?

[...]
For remove filesystems, even a local to your LAN NAS, it can take quite
a while.

Of course I meant "remote" here, not "remove".

Cheers,
Cameron Simpson <cs@cskk.id.au>

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On 12Oct2022 20:54, Jon Ribbens <jon+usenet@unequivocal.eu> wrote:

On 2022-10-12, Jon Ribbens <jon+usenet@unequivocal.eu> wrote:

On 2022-10-12, Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:

Jon Ribbens <jon+usenet@unequivocal.eu> writes:

on Amazon Linux:

$ which rm
/usr/bin/rm
$ sudo which rm
/bin/rm

Have some major Linux distributions not done usrmerge yet? For any that >>> have, /bin is a symbolic link to /usr/bin

The above example may just be a different ordering in $PATH.

I have immediate access to CentOS 7, Ubuntu 20, and Amazon Linux 2,
and none of those have done that.

Sorry, in fact they have done that - I misread your comment as being
that they had symlinked the executables not the directories. This seems
quite an unwise move to me but presumably they've thought it through.

I think that modern discs are so large these days that the scenario of
having a small critical /bin with a larger less critical /usr/bin on
another partition are behind us except in very niche circumstances.

Cheers,
Cameron Simpson <cs@cskk.id.au>

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On 2022-10-12 21:51:39 +0100, Paulo da Silva wrote:

Às 19:14 de 12/10/22, Jon Ribbens escreveu:

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.

The PATH in cron includes the directories with standard commands like
"rm" by default. If a cron job doesn't find rm, either
* rm isn't where it is supposed to be, or
* PATH has been changed.

I could do that, but I am using /etc/cron.* for convenience.

That may be a clue. Does any of the /etc/cron.* files set PATH to weird
value?

In any case I find that when debugging such problems it is helpful to
find out what the actual environment is. A simple

* * * * * nobody echo $PATH >> /tmp/path.$$

should do that.

hp

--
_ | Peter J. Holzer | Story must make more sense than reality.
|_|_) | |
| | | hjp@hjp.at | -- Charles Stross, "Creative writing
__/ | http://www.hjp.at/ | challenge!"

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Cameron Simpson <cs@cskk.id.au> writes:

On 12Oct2022 20:54, Jon Ribbens <jon+usenet@unequivocal.eu> wrote:

On 2022-10-12, Jon Ribbens <jon+usenet@unequivocal.eu> wrote:

On 2022-10-12, Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:

Jon Ribbens <jon+usenet@unequivocal.eu> writes:

on Amazon Linux:

$ which rm
/usr/bin/rm
$ sudo which rm
/bin/rm

Have some major Linux distributions not done usrmerge yet? For any that >>>> have, /bin is a symbolic link to /usr/bin

The above example may just be a different ordering in $PATH.

Sure, but the point is OP can use either /bin/rm or /usr/bin/rm on the
vast majority of systems and execute the same command.

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On 10/12/22 09:06, Chris Green wrote:

Michael F. Stemper <michael.stemper@gmail.com> wrote:

On 12/10/2022 07.20, Chris Green wrote:

jak <nospam@please.ty> wrote:

Il 12/10/2022 09:40, jkn ha scritto:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

I'm afraid you will have to look for the command in every path listed in >>>>>> the PATH environment variable.

erm, or try 'which rm' ?

You might but if you don't know where the 'rm' command is, you will have >>>> the same difficulty in using 'which' command. Do not you think?

From a command prompt use the bash built-in 'command' :-

command -v rm

... and rm will just about always be in /usr/bin.

On two different versions of Ubuntu, it's in /bin.

I think you'll find it's in both /bin and /usr/bin, usually /usr/bin
is earlier in the path so /usr/bin/rm is the one that will normally be
found first.

It's only in /bin/rm in case one has a system which mounts /bin
separately and earlier in the boot sequence and rm is one of the
commands needed early on.

ls -l /bin
lrwxrwxrwx 1 root root 7 Sep 23 01:41 /bin -> usr/bin

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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?

For now I will postpone this problem.
I just wrote a small script to delete a dir using rm and it works even
under cron!
There is another problem involved. The script, works fine except when
launched by cron! Why?
I'll have to look into this later when I have more time.
For now I solved the problem using a complementary shell script.

Thank you very much to those who responded.
Paulo

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On 13Oct2022 03:25, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

There is another problem involved. The script, works fine except when >launched by cron! Why?

Record the script output:

# record all output
exec >/tmp/script.$$.out 2>&1
# dump the envionment
env | sort
# turn on execution tracing
set -x
... rest of the script

and have a look afterwards. Cron's environment is very minimal. This
will show you what's in it.

Cheers,
Cameron Simpson <cs@cskk.id.au>

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In comp.lang.python, jkn <jkn_gg@nicorp.f9.co.uk> wrote:

On Wednesday, October 12, 2022 at 6:12:23 AM UTC+1, jak wrote:

I'm afraid you will have to look for the command in every path listed in
the PATH environment variable.

erm, or try 'which rm' ?

It is so hilarious seeing the responses to this thread. Hint: what do
you think the `which` program does?

$ touch /var/tmp/rm
$ chmod 755 /var/tmp/rm
$ env -i PATH=/etc:/usr:/lib:/var/tmp:/tmp /usr/bin/which rm
/var/tmp/rm
$ mv /var/tmp/rm /tmp/
$ env -i PATH=/etc:/usr:/lib:/var/tmp:/tmp /usr/bin/which rm
/tmp/rm
$

Elijah
------
/usr/bin/busybox rm /tmp/rm

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On 2022-10-12, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

Às 22:38 de 12/10/22, Jon Ribbens escreveu:

On 2022-10-12, Jon Ribbens <jon+usenet@unequivocal.eu> wrote:

On 2022-10-12, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> 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_ns@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.

I assume you mean /usr/bin. But it doesn't matter. As already
discussed, even if 'rm' is in /usr/bin, it will be in /bin as well
(or /usr/bin and /bin will be symlinks to the same place).

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 cannot think of any situation in which that will help you. But if for
some reason you really want to do that, you can use the shutil.which()
function from the standard library:

>>> import shutil
>>> shutil.which('rm')
'/usr/bin/rm'

Actually if I'm mentioning shutil I should probably mention
shutil.rmtree() as well, which does the same as 'rm -r', without
needing to find or run any other executables.

Except that you can't have parallel tasks, at least in an easy way.
Using Popen I just launch rm's and end the script.

[threading.Thread(target=shutil.rmtree, args=(item,)).start()
for item in items_to_delete]

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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_ns@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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On 10/11/22 22:00, Paulo da Silva wrote:

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?

There are certain standards that suggest where to look. For example,
there's the Linux Filesystem Hiearchy Standard 3.0: https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch03s04.html

In short, you want to hard code /bin for a command like rm. And yes it
will always be in /bin on any standard Linux OS.

Despite modern distros making /bin and /usr/bin the same directory, if
the target OS is anywhere close to the standard, you can always find the
basic commands in /bin. I would not hard code any script to use
/usr/bin for any basic commands and I would not use anything other than
/bin/sh or /bin/bash as the shell script shebang if you want any sort of portability.

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On Wed, Oct 12, 2022 at 11:13 AM Paulo da Silva < p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

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?

I like to test my cronjobs with something like:

env - /usr/local/bin/my-cronjob

This will empty out the environment, and force you to set $PATH yourself.

Alternatively, you can "ps axfwwe" (on Linux) to see environment variables,
and check what the environment of cron (or similar) is. It is this
environment (mostly) that cronjobs will inherit.

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On 2022-10-14 07:40:14 -0700, Dan Stromberg wrote:

Alternatively, you can "ps axfwwe" (on Linux) to see environment
variables, and check what the environment of cron (or similar) is. It
is this environment (mostly) that cronjobs will inherit.

The simplest (and IMHO also most reliable) way to find out the
environment a cronjob has is to write a cronjob which just dumps the environment.

hp

--
_ | Peter J. Holzer | Story must make more sense than reality.
|_|_) | |
| | | hjp@hjp.at | -- Charles Stross, "Creative writing
__/ | http://www.hjp.at/ | challenge!"

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On Oct 14, 2022 18:19, "Peter J. Holzer" <hjp-python@hjp.at> wrote:

On 2022-10-14 07:40:14 -0700, Dan Stromberg wrote:
> Alternatively, you can "ps axfwwe" (on Linux) to see environment
> variables, and check what the environment of cron (or similar) is.  It
> is this environment (mostly) that cronjobs will inherit.

The simplest (and IMHO also most reliable) way to find out the
environment a cronjob has is to write a cronjob which just dumps the
environment.

  

=====
Lately I've been using systemd timers instead of cronjobs. They are easier
to debug (journalctl) but require a bit more work to write. Systemd is
available on Fedora & friends and Debian based systems, maybe more. It has
no builtin MAILTO. I use an OnFailure stanza to send a Slack message with
curl instead.
https://www.freedesktop.org/software/systemd/man/systemd.timer.html
https://unix.stackexchange.com/questions/278564/cron-vs-systemd-timers

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On Mi 12 Okt 2022 at 05:00, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

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?

Why not just use os.unlink ?

'Andreas

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On Wed, Oct 12, 2022 at 9:57 PM Cameron Simpson <cs@cskk.id.au> wrote:

On 13Oct2022 03:25, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

There is another problem involved. The script, works fine except when >launched by cron! Why?

Record the script output:

# record all output
exec >/tmp/script.$$.out 2>&1
# dump the envionment
env | sort
# turn on execution tracing
set -x
... rest of the script

and have a look afterwards. Cron's environment is very minimal. This
will show you what's in it.

Careful. On some systems if someone restarts the cron daemon, it could
pick up a larger environment than after being started on boot.

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On 16 Oct 2022, at 04:53, Dan Stromberg <drsalists@gmail.com> wrote:

On Wed, Oct 12, 2022 at 9:57 PM Cameron Simpson <cs@cskk.id.au> wrote:

On 13Oct2022 03:25, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> >>> wrote:
There is another problem involved. The script, works fine except when
launched by cron! Why?

Record the script output:

# record all output
exec >/tmp/script.$$.out 2>&1
# dump the envionment
env | sort
# turn on execution tracing
set -x
... rest of the script

and have a look afterwards. Cron's environment is very minimal. This
will show you what's in it.

Careful. On some systems if someone restarts the cron daemon, it could
pick up a larger environment than after being started on boot.

That have to a old system that does not use systemd.
Is there a specific system that still does this?

Barry

--
https://mail.python.org/mailman/listinfo/python-list

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On 2022-10-16 17:21:03 +0100, Barry wrote:

On 16 Oct 2022, at 04:53, Dan Stromberg <drsalists@gmail.com> wrote:

On Wed, Oct 12, 2022 at 9:57 PM Cameron Simpson <cs@cskk.id.au> wrote:

On 13Oct2022 03:25, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> >>> wrote:
There is another problem involved. The script, works fine except when
launched by cron! Why?

[... script deleted ...]

Cron's environment is very minimal. This will show you what's in
it.

Careful. On some systems if someone restarts the cron daemon, it could pick up a larger environment than after being started on boot.

That have to a old system that does not use systemd.

Systemd is specific to Linux - and not even used by all Linux
distributions.

Is there a specific system that still does this?

Not sure. Some Unixes I've used in the past (probably including some
Linux distributions) had this problem. So you had to be a bit careful
when restarting daemons from the command line. I think the sysVinit
system used by most Linux distributions before systemd did clean up the environment if you used it correctly (but I'm not sure and have no
system anymore to test it). I haven't used Solaris or HP/UX in a long
time (and other Unixes even longer) so I don't know what they do these
days. And I've never used MacOS, I just know that they've used a system
of their own long before systemd.

Anyway he doesn't have to restart cron to add a cron-job (nor for any
other reason during normal operation), so what happens if you manually
restart cron is almost certainly irrelevant for the OP.

hp

--
_ | Peter J. Holzer | Story must make more sense than reality.
|_|_) | |
| | | hjp@hjp.at | -- Charles Stross, "Creative writing
__/ | http://www.hjp.at/ | challenge!"

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On 2022-10-15, Andreas Eder <a_eder_muc@web.de> wrote:

On Mi 12 Okt 2022 at 05:00, Paulo da Silva <p_d_a_s_i_l_v_a_ns@nonetnoaddress.pt> wrote:

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.

Why not just use os.unlink ?

Because he's using 'rm' to recursively remove a large directory tree
many levels deep.

One might think that could be done by

os.removedirs(name)
Remove directories recursively. [...]

But it doesn't appear so from the description:

Works like rmdir() except that, if the leaf directory is
successfully removed, removedirs() tries to successively remove
every parent directory mentioned in path until an error is raised
(which is ignored, because it generally means that a parent
directory is not empty). For example, os.removedirs('foo/bar/baz')
will first remove the directory 'foo/bar/baz', and then remove
'foo/bar' and 'foo' if they are empty. Raises OSError if the leaf
directory could not be successfully removed.

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