The Unix `Who` Command • Hacker News Board

Re: The Unix `Who` Command

#21

Post by forgotpwd16 » Thu, Sep 03, 2020, 4:22 PM UTC

MisterTea wrote: post #14

chard_slicks_ wrote: post #5

His "who" implementation is 73 lines (21 if you remove blank lines and comments). Compare that to 836 in GNU Coreutils[0]. [0] https://github.com/coreutils/coreutils/blob/master/src/who.c

plan 9 who is a 3 line shell script that just greps the output of ps and sorts it. You could eliminate ps and just grep through /proc but why reinvent the wheel when an existing tool already does part of the job? I see some comments here citing a lack of options, most of which appear to have nothing to do with who is logged into the machine.

Source for the mentioned script: https://github.com/0intro/plan9/blob/master/rc/bin/who. Also, other utilities implemented as scripts are fshalt (P9's shutdown), kill, lookman (P9's apropos), uptime and whois.

Re: The Unix `Who` Command

#22

Post by [deleted] » Thu, Sep 03, 2020, 4:28 PM UTC

[deleted]

Re: The Unix `Who` Command

#23

Post by jf » Thu, Sep 03, 2020, 4:33 PM UTC

forgotpwd16 wrote: post #21

MisterTea wrote: post #14

Earlier quoted context omitted.

plan 9 who is a 3 line shell script that just greps the output of ps and sorts it. You could eliminate ps and just grep through /proc but why reinvent the wheel when an existing tool already does part of the job? I see some comments here citing a lack of options, most of which appear to have nothing to do with who is logged into the machine.

Source for the mentioned script: https://github.com/0intro/plan9/blob/master/rc/bin/who . Also, other utilities implemented as scripts are fshalt (P9's shutdown), kill, lookman (P9's apropos), uptime and whois.

Does anybody know why there are line breaks in the sed command?

Re: The Unix `Who` Command

#24

Post by [deleted] » Thu, Sep 03, 2020, 4:44 PM UTC

jf wrote: post #23

forgotpwd16 wrote: post #21

Earlier quoted context omitted.

Source for the mentioned script: https://github.com/0intro/plan9/blob/master/rc/bin/who . Also, other utilities implemented as scripts are fshalt (P9's shutdown), kill, lookman (P9's apropos), uptime and whois.

Does anybody know why there are line breaks in the sed command?

[deleted]

Re: The Unix `Who` Command

#25

Post by x87678r » Thu, Sep 03, 2020, 4:51 PM UTC

formerly_proven wrote: post #2

who is 66 % waste: w is 300 % shorter and shows up to 721 % more valuable information.

who shows where the session is coming from which is useful for me where random people connect with the same system account.

(OK w -f shows this)

Re: The Unix `Who` Command

#26

Post by alpb » Thu, Sep 03, 2020, 5:03 PM UTC

chard_slicks_ wrote: post #5

His "who" implementation is 73 lines (21 if you remove blank lines and comments). Compare that to 836 in GNU Coreutils[0]. [0] https://github.com/coreutils/coreutils/blob/master/src/who.c

You'll like this Rob Pike thread https://twitter.com/rob_pike/status/966896123548872705

Re: The Unix `Who` Command

#27

Post by dn3500 » Thu, Sep 03, 2020, 5:05 PM UTC

The comment "initialize the utmp structure" is wrong. You have declared the struct here but it is uninitialized.

And there is no point in setting the locale, since your program never uses it.

Re: The Unix `Who` Command

#28

Post by tptacek » Thu, Sep 03, 2020, 5:09 PM UTC

It's funny to me, because the way I came up in Unix, `utmp` was one of the first things you learned about: you were using Unix not because you installed it but because every system you might want to break into (for instance, to get to IRC through an outdial or a gateway) was running it, and they were all multi-user shell machines, and you wanted to make sure you weren't showing up in `who`. I probably knew the `utmp` format before I knew how to use `find`.

You'll find, in archives from hacking sites of the era, a whole variety of "utmp editors".

Re: The Unix `Who` Command

#29

Post by indigodaddy » Thu, Sep 03, 2020, 5:16 PM UTC

I’ve found grep to be unreliable or behave unexpectedly with strace. Even when piping to strings first, although not sure if that is of any consequence. Anyone know why that is or experienced the same?

Re: The Unix `Who` Command

#30

Post by dn3500 » Thu, Sep 03, 2020, 5:33 PM UTC

indigodaddy wrote: post #29

I’ve found grep to be unreliable or behave unexpectedly with strace. Even when piping to strings first, although not sure if that is of any consequence. Anyone know why that is or experienced the same?

You know it outputs to stderr, right? Also if you give it the option "-o -" it doesn't do what you might expect. Other than that I grep the output of strace all the time and it works for me.