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Old 16th April 2021
phillbush's Avatar
phillbush phillbush is offline
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Default Possible bug in how OpenBSD ksh(1) handle the ERR trap

To help me identify whether a command fails and what is its exit code, I trap the ERR special signal to print the exit code of a command that returns nonzero.

Code:
trap 'printf "\e[1;31mEXIT: %s\e[0m\n" "$?"' ERR
You can try it in your shell.
Run this and then run `false` or `cat nonexistent/file.txt`.

However, OpenBSD pdksh behaves a little different from ksh93 and bash when the command terminates from a signal.

For example. Try this in bash(1) or ksh93(1): run the trap command and then run `cat` (without any arguments) and immediately type `^C` (ctrl+c) to send `SIGINT` to cat. The shell will print `EXIT: 130` (or `EXIT: 258`) right after the command is terminated and before the next prompt.

Try this again in OpenBSD ksh(1). The `EXIT: 130` string will not be printed immediately. Now enter a successful command, such as grep(1) or ls(1). NOW the error string will be printed.

This image illustrates what I am saying:

  • First, I'm on a ksh93(1) subshell.
    I run `false`, and it prints `EXIT: 1`.
    I run `cat` and type `^C` and it prints `EXIT 258`.
    I run `grep -V` and it prints nothing.
  • Then, I exit ksh93(1) and return to ksh(1).
    I run `false`, and it prints `EXIT: 1`.
    I run `cat` and type `^C` and it prints nothing.
    I run `grep -V` and it prints `EXIT 130`.

Is this a bug? If yes, is it known by the developers?
I think that it can be a problem in a script to not handle a ERR trap right after a command terminates from a signal.

Last edited by phillbush; 16th April 2021 at 09:49 PM.
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Old 16th April 2021
ibara ibara is offline
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Probably want to report this to bugs@
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Old 16th April 2021
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phillbush phillbush is offline
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Quote:
Originally Posted by ibara View Post
Probably want to report this to bugs@
I want to certify that this is not happening only with me.
Someone on #openbsd IRC channel tried to replicate the bug and nothing happened... the "EXIT: 130" string was not printed after true(1).
Could you replicate the bug?
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Old 16th April 2021
ibara ibara is offline
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On ksh(1):
false
EXIT: 1

cat
^C
(no output, but if you run echo $? you see 130)

true
(no output)
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Old 16th April 2021
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phillbush phillbush is offline
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Quote:
Originally Posted by ibara View Post
On ksh(1):
false
EXIT: 1

cat
^C
(no output, but if you run echo $? you see 130)

true
(no output)
What happens if you use a non-builtin (like ls(1)) in place of true?
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Old 17th April 2021
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Head_on_a_Stick Head_on_a_Stick is offline
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Hopefully not off-topic but this is from Alpine Linux running ibara's port of OpenBSD's ksh(1):
Code:
~$ trap 'printf "\e[1;31mEXIT: %s\e[0m\n" "$?"' ERR
~$ false
EXIT: 1
1~$ cat
^C
130~$ ls
[snip]
EXIT: 0
~$
Note my prompt, which shows the exit status of the last command if it is non-zero:
Code:
~$ echo $PS1
\e[91m${?#0}\e[0m\w\e[97m$\e[0m
~$
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Old 22nd April 2021
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phillbush phillbush is offline
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Just sent the bug to bugs@.
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