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)
