On 04/10/2017 12:46 PM, Gordon Messmer wrote:
> On 04/10/2017 11:30 AM, JD wrote:
>> On 04/10/2017 10:32 AM, Gordon Messmer wrote:
>>> On 04/09/2017 07:25 PM, JD wrote:
>>>>> ssh user_foo@1.2.3.4 "pgrep -f 'master_app' | wc -l" 2> stderr.log
>>>> Those stderr messages would be coming from wc and NOT from ssh.
>>>> The OP's command should be
>>>> ssh user_foo@1.2.3.4 2> stderr.log "pgrep -f 'master_app' | wc -l"
>> You did not understand.
>> The ssh command is executed LOCALLY and it's stderr is on the local
>> machine.
>> So, the OP will divert the LOCAL stderr to a LOCAL file so that he can
>> see if the
>> LOCAL ssh command experienced any issues with the connection.
>> Capiche?????
>
> I did understand. It doesn't matter if 2>file appears before the ssh
> arguments, or at the end. In both cases, ssh's stderr will be written
> to a local file. It is incorrect to say that the former example would
> redirect wc's stderr, and not ssh.
That's correct. In both examples, the commands inside the double quotes
and only what's inside the quotes are what's executed on the remote
system. Everything else is executed on the local system, thus these
three commands are entirely equivalent:
ssh user_foo@1.2.3.4 "pgrep -f 'master_app' | wc -l" 2> stderr.log
ssh user_foo@1.2.3.4 2>stderr.log "pgrep -f 'master_app' | wc -l"
ssh 2>stderr.log user_foo@1.2.3.4 "pgrep -f 'master_app' | wc -l"
In all three the redirection is done on ssh's stderr and it's written
to a "stderr.log" file in the current directory.
As to preferences, the second and third ones may be a bit more obvious
as to which command's stderr is being redirected but all three will
function identically. Personally, I use the first form most often (with
all redirections at the end). I think this comes from writing boatloads
of shell scripts and crontab entries. Or perhaps I'm just weird. Quite
possibly both.
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