u can try
shopt -u checkwinsize
to disable that columns settings
On Thu, Jun 13, 2024, 8:29 PM Alain BROSSARD via Bug reports for the GNU
Bourne Again SHell <bug-bash@gnu.org> wrote:
> Hi,
>
> You are correct, export COLUMNS does truncate, I had made the mistake
> of replaying the previous execution of ps which was with “axww”.
> Something does go wrong once COLUMNS is in the environment, it seems that
> in that case, it can get modified when executing a pipe’d command.
>
> As the following examples show, we have narrowed this down to two
> things
>
>
> 1. set -a causes, in certain situation, to be clarified, but the
> pipe below gives us a big hint, the COLUMNS variable to be exported when it
> should NOT be
> 2. COLUMNS gets modified, by the shell, when a command with a ‘|’ is
> processed
> 3. Those two conditions trigger what I saw as a bug in the output of
> “ps ax”. Now it seems that “ps” is the revealer and not buggy as I
> suspected at some point.
>
> Starting a new bash :
>
> host:/$ export COLUMNS=60
> host:/$ ps ax | grep java | head -1
> 2051669 ? Sl 0:17 /usr/lib/jvm/java-17-openjdk-am
> host:/$ export COLUMNS=80
> host:/$ ps ax | grep java | head -1
> 2051669 ? Sl 0:17 /usr/lib/jvm/java-17-openjdk-amd64/bin/java
> -Xms2g
> host:/$ export COLUMNS=120
> host:/$ ps ax | grep java | head -1
> 2051669 ? Sl 0:17 /usr/lib/jvm/java-17-openjdk-amd64/bin/java
> -Xms2g -Xmx2g -server -XX:+UseG1GC -XX:MaxGCPau
> host:/$ ps ax | grep java | head -1 ### next output should be
> the same as previous, but it is truncated
> 2051669 ? Sl 0:17 /usr/lib/jvm/java-17-openjdk-amd64/bin/java
> -Xms2g -Xmx2g -server -XX:+Us
> host:/$ echo $COLUMNS # COLUMNS was reset by bash
> 102
>
> My conclusion is that the variable COLUMNS gets “reset” when there is a
> pipe in a command and further gets EXPORTED if “set -a” was set before hand
> :
>
> host:/$ COLUMNS=80
> host:/$ echo $COLUMNS
> 80
> host:/$ echo $COLUMNS
> 80
> host:/$ echo $COLUMNS | cat
> 80
> host:/$ echo $COLUMNS
> 102
>
> PS1 is :
> \[\e]0;\u@\h: \w\a\]${debian_chroot:+($debian_chroot)}\u@\h:\w\$
>
> I would challenge the fact that “set -a” should move COLUMNS to the
> environment when it gets modified by bash itself : not the expected
> behaviour.
> @ Robert Elz, the POSIX definition does put an additional spin to this. I
> was going by the very short explanation of set -a in the bash man page.
> And I would challenge the fact that COLUMNS gets modified when a
> command with a ‘|’ is executed. There is no way for a bash user or bash
> script writer to expect such a behaviour in unforeseen circumstances. Also,
> it basically makes “set -a” too dangerous to use, so why bother
> implementing it if it shouldn’t be used ? That last bit is maybe a bit of
> a stretch, but you met my meaning.
>
> I do believe that this must be considered as a bug as it breaks scripts
> which otherwise work perfectly. I added the following line in a file which
> is getting source’d to define variables. I was not aware that the caller
> had set “-a”. In fact, scripts should not be so vulnerable to a change to
> a bash variable made by the caller. ( I did describe a work-around using
> “echo $-“ within a $( command ) in my bug report.)
>
> echo $PATH | grep -q xx/scripts || PATH=${PATH}:/xx/scripts
>
> I do not believe that adding this to a bash file should cause a failure
> 100’s of lines down in a totally different script bought from a third party
> whose use of “set –a” I do not control. I do agree, now that I know about
> this highly unexpected feature, that the third party should have used “ps
> axww”, but then how could they expect the COLUMNS variable to be exported
> ? There is no testing in the world which would catch a case like this.
> Hence, I do insist that this is a bug.
>
> The only way to prevent the ‘|’ from modifying COLUMNS is to put the
> command within $( ) from my empirical testing which is worth what it is
> worth.
>
> Not straight forward…
>
> Regards,
> Alain Brossard
>
>
>
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> From: Oğuz <oguzismailuy...@gmail.com>
> Sent: Thursday, June 13, 2024 5:34 PM
> To: Alain BROSSARD <abross...@reyl.com>
> Cc: bug-bash@gnu.org
> Subject: Re: it, soRE: set -a leads to truncated output from ps
>
> On Thursday, June 13, 2024, Alain BROSSARD <abrossard@ reyl. com> wrote:
> export COLUMNS=60 ps ax | grep java The output isn’t truncated. It is on my
> machine. You must have something in your PS1/PROMPT_COMMAND interfering. It
> is critical that
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> On Thursday, June 13, 2024, Alain BROSSARD <abross...@reyl.com<mailto:
> abross...@reyl.com>> wrote:
> export COLUMNS=60
> ps ax | grep java
>
> The output isn’t truncated.
> It is on my machine. You must have something in your PS1/PROMPT_COMMAND
> interfering.
> It is critical that application’s behaviour do not get impacted by the
> shell used to call them.
> Even more reason to use `ps axww' instead of `ps ax'.
> What do you think ?
> I think there's at least one Bash bug involved here.
>
>
> --
> Oğuz
>
>
