Bash shell `PROMPT_COMMAND` breaks after giving specific command

[kx1t]

Creating a bug report/issue

• I have searched the existing open and closed issues

Required Information

• DietPi version | 9.11 RC2 master/MichaIng
• Distro version | bookworm 0
• Kernel version | Linux coriovallum 6.12.20+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.12.20-1+rpt1~bpo12+1 (2025-03-19) aarch64 GNU/Linux
• SBC model | RPi 4 Model B (aarch64) 4Gb
• Power supply used |
• SD card used | Samsung Evo Endurance 128 Gb

Additional Information (if applicable)

• I replicated this issue on 2 other machines with DietPi 9.11RC2 (1x RPi4B/4Gb, 1x Intel x86 machine)

Steps to reproduce

1. Open a bash shell into a non-root account
2. Check that all works fine by giving some random commands
3. Provide this command: if [[ ]]; then echo true; else echo false; fi
4. Observe error messages printed after each subsequent command

-bash: PROMPT_COMMAND: line 38: syntax error near unexpected token `-w'
-bash: PROMPT_COMMAND: line 38: `[[ -w '/tmp/dietpi-process.pid' ]] && rm -f /tmp/dietpi-process.pid &> /dev/null && echo -ne '\r\e[J'; '

5. Log out, log in, repeat steps 2-4 to replicate the issue
6. To stop seeing the issue within the same shell (without logging out), type any text and then interrupt with CTRL-C before pressing the <Return key

Expected behaviour

• Command should return within the expected behavior of bash without any subsequent issues

Actual behaviour

• After each subsequent command, the error message (see below) is printed
• After waiting for some time, the error message is no longer printed after a command

Extra details

See this sequence:

pi@coriovallum:~$ echo hello
hello
pi@coriovallum:~$ echo this is a test
this is a test
pi@coriovallum:~$ if [[ ]]; then echo true; else echo false; fi
-bash: PROMPT_COMMAND: line 37: syntax error near unexpected token `-w'
-bash: PROMPT_COMMAND: line 37: `[[ -w '/tmp/dietpi-process.pid' ]] && rm -f /tmp/dietpi-process.pid &> /dev/null && echo -ne '\r\e[J'; '
pi@coriovallum:~$ echo hello
hello
-bash: PROMPT_COMMAND: line 38: syntax error near unexpected token `-w'
-bash: PROMPT_COMMAND: line 38: `[[ -w '/tmp/dietpi-process.pid' ]] && rm -f /tmp/dietpi-process.pid &> /dev/null && echo -ne '\r\e[J'; '
pi@coriovallum:~$ echo this is a test
this is a test
-bash: PROMPT_COMMAND: line 39: syntax error near unexpected token `-w'
-bash: PROMPT_COMMAND: line 39: `[[ -w '/tmp/dietpi-process.pid' ]] && rm -f /tmp/dietpi-process.pid &> /dev/null && echo -ne '\r\e[J'; '
pi@coriovallum:~$ some-random-text^C
pi@coriovallum:~$ echo hello this is a test
hello this is a test
pi@coriovallum:~$

[Joulinar]

ok and where is this an issue with DietPi? Because DietPi themselves is not an own os, it's a set of bash script on top of Debian.

[kx1t]

It only happens in DietPi and the error message clearly refers to something that DietPi must have added:

-bash: PROMPT_COMMAND: line 39: `[[ -w '/tmp/dietpi-process.pid' ]] && rm -f /tmp/dietpi-process.pid [...]

EDIT -- specifically here:
https://github.com/MichaIng/DietPi/blob/master/rootfs/etc/bashrc.d/dietpi.bash#L66

[MichaIng]

Yeah, this is added to abort the G_DIETPI-NOTIFY -2 processing animation in case the calling script is SIGKILLed or otherwise terminated a way where it cannot finish its EXIT trap anymore. Not elegant, but the best way I could find to assure there will never be an endlessly running processing animation left. I need to review this at some point.

However, the issue you face is due to [[ ]] not being a valid bash command. I leaves the [[ bash conditional open, ]] closes it only if there is any argument in between. This renders the PROMPT_COMMAND invalid. Interesting behavior. Can be fixed by either additionally close the conditional with ]] or finish the (invalid) command with ; or abort it with CTRL+C as you did. A ; in front of the PROMPT_COMMAND should fix it DietPi-wise. Let me test .... hmm no a leading ; is no valid syntax in general 🤔.

We need to find a better way to handle the processing animation, not using PROMPT_COMMAND as last resort. But a non-closing bash conditional in console is at least a rare case.