[kwlug-disc] Question about `ps` and `grep`

[Chris Craig]

It's simply that the string "[t]mux" doesn't match the regex "[t]mux"

On Wed, Sep 25, 2024 at 9:07 PM Ronald Barnes via kwlug-disc <
kwlug-disc at kwlug.org> wrote:

>
> I watched a recent video about bash on YouTube channel "You Suck At
> Programming" and a comment there has me completely baffled.
>
>
> The topic was `pgrep` and `pkill` instead of `ps aux | grep ...`.
>
>
> The comment had a solution to seeing the `grep` command in the output
> when grep'ing `ps` output:
>
> This shows the grep command in the output:
>
>
> # ps aux | grep  tmux
> root        9032  0.0  0.0  23476  5632 pts/1    S+   Sep05   0:04 sudo
> tmux new -s w00
> root        9041  0.0  0.0  23476  1560 pts/9    Ss   Sep05   0:00 sudo
> tmux new -s w00
> root        9042  0.0  0.0  10916  3712 pts/9    S+   Sep05   0:00 tmux
> new -s w00
> root        9045  0.0  0.0  14236  4920 ?        Ss   Sep05   1:14 tmux
> new -s w00
> root      748047  0.0  0.0   9212  2560 pts/10   S+   17:59   0:00 grep
> --color=auto --directories=skip tmux
>
>
>
> BUT, changing what's being grep'd for by making it [t]mux:
>
> # ps aux | grep  [t]mux
> root        9032  0.0  0.0  23476  5632 pts/1    S+   Sep05   0:04 sudo
> tmux new -s w00
> root        9041  0.0  0.0  23476  1560 pts/9    Ss   Sep05   0:00 sudo
> tmux new -s w00
> root        9042  0.0  0.0  10916  3712 pts/9    S+   Sep05   0:00 tmux
> new -s w00
> root        9045  0.0  0.0  14236  4920 ?        Ss   Sep05   1:14 tmux
> new -s w00
>
>
> Now grep's output is NOT shown.
>
>
> And I cannot figure out why not?!?
>
>
> I understand that [t] is a character range (of one character), but
> without explicit anchoring, why does that work?
>
>
>
> Anyone able to explain this?
>
>
> (Also, https://www.youtube.com/@yousuckatprogramming channel is highly
> recommended - 3 to 4 minute videos, usually about `bash` topics, where
> there's always something I learn.
>
> Then check the comments for user "extrageneity", who expands on the
> topic with a Uni CS level comment.)
>
>
> Thanks,
>
> rb
>
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