Re: Redirect a backgrounded process' stdout toward COPROC's stdin

[Davide Baldini]

On 06/03/12 17:01, Geir Hauge wrote:
> 2012/6/3 Davide Baldini <baldiniebaldini@gmail.com>:
>> Description:
>> In the following test script I run an elementary coprocess to which the
>> echo built-in, run in background, attaches its standard-output:
>>
>>    #!/bin/bash
>>    # TEST 1
>>    coproc /bin/sleep 100
>>    echo >&${COPROC[1]} &
>>
>> The script always fails, for no apparent reason, giving the output:
>>
>>    ./test.sh: line 4: ${COPROC[1]}: Bad file descriptor
> 
> The coproc fds are only available in the same shell. The subshell
> created with & cannot use them.
> 
> 
>> I wonder if the correct syntax should be rather this one (ampersand
>> moved before redirection):
>>
>>    #!/bin/bash
>>    # TEST 2
>>    coproc /bin/sleep 100
>>    echo & >&${COPROC[1]}
> 
> This is equivalent to
> 
> echo &
>> &${COPROC[1]}
> 
> & ends the command, so the redirection is not applied to the echo.
> 
> 
> See http://wiki.bash-hackers.org/syntax/keywords/coproc
> 

Thank you Geir, I really appreciated you help and the useful
bash-hackers.org link. Definitely, the GNU Bash manual would need some
deeper details on these niche features.