how output `ps aux | grep aUser` and keeping Newline ?
from Gordon_F@lemmy.ml to linux@lemmy.ml on 02 Oct 2024 07:48
https://lemmy.ml/post/20938026

Hi,

by doing a

ps aux | grep UserName

The output do not keep the LF[^1] 😡

I’ve found some solution online by they involve 3 or more pipe | !

On my side, I’ve made this

ps -fp $(pgrep -d, -u UserName)

But still I found it not super human readable.

Is their a native way with ps to filter users ? or to grep it but the keep the LF ?

[^1]: linefeed en.wikipedia.org/wiki/Linefeed#Representation

#linux

threaded - newest

thingsiplay@beehaw.org on 02 Oct 2024 08:30 next collapse

If I do ps aux | grep root, then the newline is preserved. So I’m not sure what exactly the problem is. There is a user option for ps, but it does not work with aux, ps --user root . You can ps ax --user root, but I’m not sure if this output is what you want.

Btw if you grep, then I recommend using ^user , so it only matches the beginning of each line (the actual username), as ps aux | \grep ^root (notice the backslash). Do you have an alias for grep? Try \grep instead. The backslash in front of the command will use the actual command and ignore your alias.

thingsiplay@beehaw.org on 02 Oct 2024 08:43 collapse

Here is a little bonus to have in mind: You can convert newline characters to null, then grep with option null, and at last convert null characters back to newline. Now I don’t think its useful in this case, but its good to know; therefore its a bonus information:

ps aux | tr '\n' '\0' | \grep --null-data ^root | tr '\0' '\n'
huf@hexbear.net on 02 Oct 2024 09:04 next collapse

what do you mean the output doesnt keep the LF? what LF?

ps also has -u and -U switches to filter by users

RavuAlHemio@lemmy.world on 02 Oct 2024 09:05 next collapse

ps outputs a newline after every entry. What are you trying to accomplish?

Do you have a username that contains a newline character? If so… why?!

ogeist@lemmy.dbzer0.com on 02 Oct 2024 12:55 collapse

Security by overcomplication

RavuAlHemio@lemmy.world on 02 Oct 2024 16:12 collapse

Kinda hard to encode it in /etc/passwd, which separates entries with newlines and fields of an entry with colons.

Of course, you can activate some alternative user database in /etc/nsswitch.conf and then you can have your usernames with newlines in them, but at least half of the tools on your system that process usernames will take that personally…

blashork@hexbear.net on 02 Oct 2024 13:26 next collapse

tbh you should prolly use pgrep instead of piping ps into grep

Para_lyzed@lemmy.world on 03 Oct 2024 22:42 collapse

I’m not really sure what it is you’re asking for here. As another commenter said, ps outputs a list of newline separated entries (using \n, the standard LF character). I even ran some sanity checks to make sure it wasn’t using \r\n (CR LF) with the following:

$ ps aux | grep $USER | tr -cd "\n" | wc -m
14
$ ps aux | grep $USER | tr -cd "\r" | wc -m
0

The output of ps aux | grep $USER is consistent with the formatting of ps aux. I also found that ps aux | grep $USER was consistent with ps -fp $(pgrep -d, -u $USER) except that ps -fp $(pgrep -d, -u $USER) shows the header (UID PID PPID C STIME TTY TIME CMD), does not show the processes related to the command (entries of ps aux and grep --color=auto $USER), and does not show grep’s keyword matching by highlighting all matches within a line. It is otherwise completely identical.

Can you provide the output that you are getting that is unsatisfactory to you? I don’t think I can otherwise understand where the issue is.