[arch-projects] Fwd: [initscripts] [PATCH] Setting Locale: fix status reporting FAIL erroneously

[Tom Gundersen]

On Sun, Jun 26, 2011 at 4:06 PM, Dave Reisner <d at falconindy.com> wrote:
> On Sun, Jun 26, 2011 at 03:12:24PM +0200, Kurt J. Bosch wrote:
>> Tom Gundersen, 2011-06-26 13:51:
>> >On Sun, Jun 26, 2011 at 1:03 PM, Kurt J. Bosch
>> ><kjb-temp-2009 at alpenjodel.de>  wrote:
>> >>The following test case (run in a terminal)
>> >>
>> >>#!/bin/bash
>> >>
>> >># custom override example
>> >>stat_busy() {
>> >>        if (( PUSH_MSG )); then
>> >>                # This triggers the error in "$@" below
>> >>                # actual code was:
>> >>                # echo set message "$1">  "$spl_fifo"&
>> >>                :&
>> >>        fi
>> >>        echo "$1" BUSY
>> >>}
>> >>
>> >>status() {
>> >>        stat_busy "$1"
>> >>        shift
>> >>        "$@"
>> >>        local retval=$?
>> >>        (( retval == 0 ))&&  echo DONE || echo FAIL "($retval)"
>> >>}
>> >>
>> >>PUSH_MSG=0 status "test #0" cat<(echo foo)
>> >>PUSH_MSG=1 status "test #1" cat<(echo foo)
>> >
>> >[...]
>> >
>> >>CCing Tom Gundersen.
>> >
>> >Thanks.
>> >
>> >I have not figured it out, but here is a more minimal test:
>> >
>> >
>> >#!/bin/bash
>> >
>> >
>> >test_one() {
>> >        : &
>> >        "$@"
>> >}
>> >
>> >test_two() {
>> >        :
>> >        "$@"
>> >}
>> >
>> ># working
>> >test_one eval 'cat<(echo foo)'
>> >test_two cat<(echo foo)
>> >
>> >#not working
>> >test_one cat<(echo foo)
>>
>> Confirmed.
>>
>> --
>> Kurt
>
> Now I see it (at least in Tom's example). It's expected behavior. You're
> only allowed to read the file descriptor created by a PE once. However,
> because file descriptors are inherited by subshells, when the subshell
> ends, the file descriptor is closed and it goes away. Look at what
> happens when you modify the script slightly:
>
> -------------------
>
> #!/bin/bash
>
> test_one() {
>  ls /dev/fd/
>  : &
>  ls /dev/fd/
>  "$@"
> }
>
> test_one cat <(echo foo)
>
> -------------------
>
> And then run it with debug output....
>
> +foo[11]: test_one cat /dev/fd/63
> +foo[4]: ls /dev/fd/
> ++foo[11]: echo foo
> 0  1  2  3  63
> +foo[6]: ls /dev/fd/
> +foo[5]: :
> 0  1  2  3
> +foo[7]: cat /dev/fd/63
> cat: /dev/fd/63: No such file or directory
>
> The subshell inherits the descriptor and closes it on exit, destroying
> it for the parent. The eval "works" because the FD for the process
> substitution isn't created until _after_ the subshell.
>
> Can we _not_ do this? Our old solution didn't require voodoo like this,
> and it worked just fine (albeit a few more SLOC). Not everything needs
> to be a one line operation. Perhaps we could just write a simple
> function to take care of all these 1 line files that we write to:
>
> write_oneline_file() {
>  local file=$1 line=$2 mode=$3
>
>  printf '%s\n' "$line" >"$file"
>  [[ $mode ]] && chmod "$mode" "$file"
> }
>
> Which satisfies both parties, as it appears to be a one liner in
> execution, but it's actually sane on the back end.

Thanks for your explanation Dave. I like your solution, should make
things more readable.

-t

[sorry for duplicate, forgot CC]