Re: BASH_COMMAND does not expand correctly in subshells inside traps.

[Emanuele Torre]

>   And noticed that $BASH_COMMAND always expanded to:
>
>     read -p "[...:...] $BASH_COMMAND?
>
>   where the ...:... is the expanded value of $BASH_SOURCE:$LINENO.

Err, sorry about that. I misremembered.

It is actually expanding to

  read -p "[$BASH_SOURCE:$LINENO] $BASH_COMMAND"

as it would normally do when used outside of a trap.

The rest of the issue is still valid.


On 04/11/2021, Emanuele Torre <torreemanuele6@gmail.com> wrote:
> Configuration Information [Automatically generated, do not change]:
> Machine: x86_64
> OS: linux-gnu
> Compiler: gcc
> Compilation CFLAGS: -march=x86-64 -mtune=generic -O2 -pipe -fno-plt
> -DDEFAULT_PATH_VALUE='/usr/local/sbin:/usr/local/bin:/usr/bin'
> -DSTANDARD_UTILS_PATH='/usr/bin' -DSYS_BASHRC='/etc/bash.bashrc'
> -DSYS_BASH_LOGOUT='/etc/bash.bash_logout'
> -DNON_INTERACTIVE_LOGIN_SHELLS
> uname output: Linux t420 5.10.75-1-lts #1 SMP Wed, 20 Oct 2021
> 11:02:09 +0000 x86_64 GNU/Linux
> Machine Type: x86_64-pc-linux-gnu
>
> Bash Version: 5.1
> Patch Level: 8
> Release Status: release
>
> Description:
>   BASH_COMMAND does not expand to the expected value when used in a
>   subshell inside a trap.
>
>   I tried using the following DEBUG trap that i got from
>   http://mywiki.wooledge.org/BashGuide/Practices in bash-5.1:
>
>     trap '(read -p "[$BASH_SOURCE:$LINENO] $BASH_COMMAND?")' DEBUG
>
>   And noticed that $BASH_COMMAND always expanded to:
>
>     read -p "[...:...] $BASH_COMMAND?
>
>   where the ...:... is the expanded value of $BASH_SOURCE:$LINENO.
>
>   Then I tried to use the same trap in bash-4.4 and it worked as
>   expected.
>
> Repeat-By:
>
>   $ cat test1
>   trap 'echo "$BASH_COMMAND"' DEBUG
>   echo hello
>   $ cat test2
>   trap '(echo "$BASH_COMMAND")' DEBUG
>   echo hey
>   bash
>
>   $ ./bash test1 # bash-4.4
>   echo hey
>   hey
>   $ ./bash test2 # bash-4.4
>   echo hey
>   hey
>   $ bash test1 # bash-5.1
>   echo hey
>   hey
>   $ bash test2 # bash-5.1
>   echo "$BASH_COMMAND"
>   hey
>
>   $ ./bash --version | head -1
>   GNU bash, version 4.4.0(3)-release (x86_64-unknown-linux-gnu)
>   $ bash --version | head -1
>   GNU bash, version 5.1.8(1)-release (x86_64-pc-linux-gnu)
>