>From the reference.
Lets examine that step by step.
|( ( ( ( someprog; #part6
echo $? >&3 #part5
) | filter >&4 #part4
) 3>&1 #part3
) | stdintoexitstatus #part2
) 4>&1 #part1|
>From bottom up:
1. A subshell is created with file descriptor 4 redirected to stdout.
This means that whatever is printed to file descriptor 4 in the
subshell will end up as the stdout of the entire construct.
2. A pipe is created and the commands on the left (|#part3|) and right
(|stdintoexitstatus|) are executed. |stdintoexitstatus| is also the
last command of the pipe and that means the exit status
of |stdintoexitstatus| will be the exit status of the entire construct.
3. A subshell is created with file descriptor 3 redirected to stdout.
This means that whatever is printed to file descriptor 3 in this
subshell will end up in |stdintoexitstatus| and in turn will be the
exit status of the entire construct.
4. A pipe is created and the commands on the left
(|#part5| and |#part6|) and right (|filter >&4|) are executed. The
output of |filter| is redirected to file descriptor 4.
In |#part1| the file descriptor 4 was redirected to stdout. This
means that the output of |filter| is the stdout of the entire construct.
5. Exit status from |#part6| is printed to file descriptor 3.
In |#part3| file descriptor 3 was redirected to|stdintoexitstatus|.
This means that the exit status from |#part6| will be the final exit
status for the entire construct.
6. |someprog| is executed. The exit status is taken in |#part5|. The
stdout is taken by the pipe in|#part4| and forwarded to |filter|.
The output from |filter| will in turn reach stdout as explained
in|#part4|
On 10/01/2013 03:34 PM, Paul Ingram wrote:
> Why the redirect from descriptor 4?
>
> :: psi
>
> On Oct 1, 2013, at 3:13 PM, Duffie Cooley <dcoo...@nicira.com> wrote:
>
>> What about this?
>>
>> referenced from here.
>>
>> http://unix.stackexchange.com/questions/14270/get-exit-status-of-process-thats-piped-to-another/70675#70675
>>
>> diff --git a/utilities/ovs-lib.in b/utilities/ovs-lib.in
>> index 1684ddc..5286e12 100644
>> --- a/utilities/ovs-lib.in
>> +++ b/utilities/ovs-lib.in
>> @@ -41,6 +41,11 @@ ovs_ctl_log () {
>> echo "$@" >> "${logdir}/ovs-ctl.log"
>> }
>>
>> +stdintoexitstatus () {
>> + read exitstatus
>> + return $exitstatus
>> +}
>> +
>> ovs_ctl () {
>> case "$@" in
>> *"=strace"*)
>> @@ -51,7 +56,7 @@ ovs_ctl () {
>> ;;
>> *)
>> echo "`date -u`:$@" >> "${logdir}/ovs-ctl.log"
>> - "${datadir}/scripts/ovs-ctl" "$@" 2>&1 | tee -a
>> "${logdir}/ovs-ctl.log"
>> + (((("${datadir}/scripts/ovs-ctl" "$@" 2>&1 ; echo $? > &3)
>> | tee -a "${logdir}/ovs-ctl.log" ) 3>&1) | stdintoexitstatus) 4>&1
>> ;;
>> esac
>> }
>>
>>
>> Thanks,
>>
>> Duffie
>>
>>
>> On 10/01/2013 11:48 AM, Gurucharan Shetty wrote:
>>> This patch works for me, but it is a little hacky.
>>>
>>> diff --git a/utilities/ovs-lib.in b/utilities/ovs-lib.in
>>> index 1684ddc..b0cdaf2 100644
>>> --- a/utilities/ovs-lib.in
>>> +++ b/utilities/ovs-lib.in
>>> @@ -51,7 +51,13 @@ ovs_ctl () {
>>> ;;
>>> *)
>>> echo "`date -u`:$@" >> "${logdir}/ovs-ctl.log"
>>> - "${datadir}/scripts/ovs-ctl" "$@" 2>&1 | tee -a
>>> "${logdir}/ovs-ctl.log"
>>> + unique=`(uuidgen) 2>/dev/null` || unique=`date +"%Y %b %d %T"`
>>> + mkfifo "/tmp/${unique}"
>>> + tee -a "${logdir}/ovs-ctl.log" < "/tmp/${unique}" &
>>> + "${datadir}/scripts/ovs-ctl" "$@" > "/tmp/${unique}" 2>&1
>>> + rc=$?
>>> + rm "/tmp/${unique}"
>>> + return $rc
>>> ;;
>>> esac
>>> }
>>>
>>> On Tue, Oct 1, 2013 at 10:11 AM, Gurucharan Shetty <shet...@nicira.com>
>>> wrote:
>>>> On Mon, Sep 30, 2013 at 7:27 PM, Duffie Cooley <dcoo...@nicira.com> wrote:
>>>>> From: Duffie Cooley <dcoo...@nicira.com>
>>>>> This is a fix for a request to make sure that the openvswitch status
>>>>> command
>>>>> in rhel based distros gives a useful exit status. That was fixed in
>>>>>
>>>>> commit 5e0c05bc058c78a11be6747f62e6ad88e5d06b70
>>>>> debian: Fix exit status of openvswitch-switch init script "status" command
>>>>>
>>>>>
>>>>>
>>>>> Signed-off-by: Duffie Cooley <dcoo...@nicira.com>
>>>>> ---
>>>>> rhel/etc_init.d_openvswitch | 3 ++-
>>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/rhel/etc_init.d_openvswitch b/rhel/etc_init.d_openvswitch
>>>>> index 7e64132..6a53cef 100755
>>>>> --- a/rhel/etc_init.d_openvswitch
>>>>> +++ b/rhel/etc_init.d_openvswitch
>>>>> @@ -5,7 +5,7 @@
>>>>> # chkconfig: 2345 09 91
>>>>> # description: Manage Open vSwitch kernel modules and user-space daemons
>>>>>
>>>>> -# Copyright (C) 2009, 2010, 2011 Nicira, Inc.
>>>>> +# Copyright (C) 2009, 2010, 2011, 2013 Nicira, Inc.
>>>>> #
>>>>> # Licensed under the Apache License, Version 2.0 (the "License");
>>>>> # you may not use this file except in compliance with the License.
>>>>> @@ -81,6 +81,7 @@ case $1 in
>>>>> ;;
>>>>> status)
>>>>> ovs_ctl status
>>>>> + exit $?
>>>>> ;;
>>>>> version)
>>>>> ovs_ctl version
>>>>> --
>>>>> 1.8.1.2
>>>>>
>>>> I don't think this helps. The exit status is always 0. I broke this
>>>> with my implementation of 'ovs_ctl' in ovs-lib tee'ing the o/p to
>>>> ovs-ctl.log. tee will return an exit status of success even though the
>>>> previous command returned an exit status of 1.
>>>>
>>>> I can use the PIPESTATUS variable. But I don't think it is POSIX
>>>> compliant. Any other ideas?
>>>>
>> _______________________________________________
>> dev mailing list
>> dev@openvswitch.org
>> http://openvswitch.org/mailman/listinfo/dev
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