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

[Geir Hauge]

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

-- 
Geir Hauge