[debbugs-tracker] bug#22205: closed (tee bug?)

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Your message dated Fri, 18 Dec 2015 09:43:51 -0700
with message-id <address@hidden>
and subject line Re: bug#22205: tee bug?
has caused the debbugs.gnu.org bug report #22205,
regarding tee bug?
to be marked as done.

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22205: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=22205
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--- Begin Message --- Subject: tee bug? Date: Fri, 18 Dec 2015 14:18:07 +0100 User-agent: Mozilla/5.0 (X11; Linux i686; rv:38.0) Gecko/20100101 Thunderbird/38.4.0

Hi team,

I detected an strange behaviour of tee command that may bee a bug.

Please consider this script snippet

VAR=""

A() {
    VAR="This is my value"   
    echo "VAR in $FUNCNAME: $VAR"
}

BA() {
    A | tee /tmp/kk
    echo "VAR in $FUNCNAME: $VAR"
}

This is the output when when executed:

$ BA
VAR in A: This is my value
VAR in BA:

I miss the value of VAR inside BA function.



In fact if "| tee /tmp/kk" is removed value of VAR is properly visible from BA function:

VAR=""

A() {
    VAR="This is my value"   
    echo "VAR in $FUNCNAME: $VAR"
}

BA() {
    A
    echo "VAR in $FUNCNAME: $VAR"
}


$ BA
VAR in A: This is my value
VAR in BA: This is my value

Many thanks for your priceless effort,
Nacho

Juan Ignacio Esteban

Integration Architect & Security Officer | Integration Centre of Expertise

Walgreens Boots Alliance - Enterprise IT Shared Services - Retail Pharmacy International & Pharmaceutical Wholesale

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--- Begin Message --- Subject: Re: bug#22205: tee bug? Date: Fri, 18 Dec 2015 09:43:51 -0700 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

tag 22205 notabug
thanks

On 12/18/2015 06:18 AM, Nacho Esteban wrote:
> Hi team,
> 
> I detected an strange behaviour of tee command that may bee a bug.

Not a bug in tee, but intentional behavior of your shell.

> 
> Please consider this script snippet
> 
>    VAR=""
> 
>    A() {
>         VAR="This is my value"
>         echo "VAR in $FUNCNAME: $VAR"
>    }
> 
>    BA() {
>         A | tee /tmp/kk

You are using a pipeline.  Shells implement pipelines by running the
left command (here, the function A) in a subshell. (POSIX also says that
the right command can also be a subshell, but there it is not required;
ksh runs the right command in the current shell, and bash used to run it
in a subshell but new enough bash now has a knob you can turn on to
emulate ksh behavior).

Therefore, all changes to the environment made during the execution of A
are local to that subshell, and are lost as soon as the subshell exits.

>         echo "VAR in $FUNCNAME: $VAR"

Thus, here you print the value of $VAR as it was before A ran, since
running A does not affect the current shell.


> In fact if "| tee /tmp/kk" is removed value of VAR is properly visible
> from BA function:

Because then you no longer have a subshell, so now the execution of
function A affects the current shell.  Again, not tee's fault.  You
could replace it with "| :" and see the same effect.

> This e-mail (including any attachments) is confidential and may be
> privileged or

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-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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