Re: [[ and set -E vs trap ERR

[Chet Ramey]

Isaac Good wrote:
> Configuration Information [Automatically generated, do not change]:
> Machine: i686
> OS: linux-gnu
> Compiler: gcc
> Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i686' 
> -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i686-pc-linux-gnu' 
> -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -         DPACKAGE='bash' 
> -DSHELL -DHAVE_CONFIG_H   -I.  -I. -I./include -I./lib   -march=i686 
> -mtune=generic -O2 -pipe
> uname output: Linux arch 2.6.31-ARCH #1 SMP PREEMPT Fri Oct 23 11:12:58 CEST 
> 2009 i686 Pentium III (Katmai) GenuineIntel GNU/Linux
> Machine Type: i686-pc-linux-gnu
> 
> Bash Version: 4.0
> Patch Level: 35
> Release Status: release
> 
> cat <<-EOF >test
>       #!/bin/bash -e
>       set -E
>       trap 'echo >&2 "error"' ERR
> 
>       echo TEST1
>       if [ $(false) ] ; then
>                       echo 1
>       fi
> 
>       echo TEST2
>       if [[ $(false) ]] ; then
>                       echo 1
>       fi
> EOF
> 
> Expected output:
> TEST1
> TEST2
> 
> Actual output:
> TEST1
> TEST2
> error
> 
> The [[ masks the fact that an 'if' is running - but only in regards to the 
> trap. bash does not exit on this error but the trap is triggered. 
> [ works fine.
> With set -E, the trap is inherited by command substitution, but the fact that 
> the trap is suppressed is not.
> 
> <\amethyst> but the manpage says the ERR trap is avoided under "the same 
> conditions obeyed by the errexit option", so at least the documentation is in 
> error if nothing else

In bash-4.0, the conditional command does not honor the set -e option,
and as a result, doesn't pay attention to set -E either.  The [[ and
(( commands will honor set -e in bash-4.1.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/