C wrapper to remove users on command "ps"

Question

I have one question maybe someone here can help me. If i do "ps aux --sort user" on linux console I have one list of users and their processes runing on the machine. My question is how do I remove the users name and print that list like this in a C program:

for example:

(…)
--------------------------------------------------------------------------
user: APACHE
--------------------------------------------------------------------------
3169 0.0 1.2 39752 12352 ? S 04:10 0:00 /usr/sbin/httpd
--------------------------------------------------------------------------
user: VASCO
--------------------------------------------------------------------------
23030 0.0 0.1 4648 1536 pts/1 Ss 20:02 0:00 –bash

(…)

I print the user name then I print his processes... any ideas ?

thx

Answer 1

ps aux --sort user | perl -npe 's/^(\w+)//g; if ($user ne $1) {$user=$1; print "user: " . uc($user) . "\n";}'

Answer 2

Not really an answer to your question, but user names are case-sensitive in unix, so capitalising them all probably isn't a good idea. If you want to make them stand out visually then "USER: apache" would be better.

Apart from that bmdhacks' answer is good (but not quite right). You could do something similar in awk, but it would be rather more complicated.

Answer 3

This should work:

ps haux --sort user | perl -npe 's/^(\S+)\s+//; if ($user ne $1) {$user=$1; print "user: " . uc($user) . "\n";}'

Based on bmdhacks's answer, but with the following fixes:

a) it counts any non-whitespace as part of the user name, b) it deletes any whitespace after the user name, like your example output had, otherwise things wouldn't line up c) I had to remove the g to get it to work. I think because with the g it can potentially match lots of times, so perl doesn't set $1 as it could be ambiguous. d) Added h to the ps command so that it doesn't output a header.

Answer 4

that's command line for linux to make what i said... but that's not what i want... i want to make that in some C program... I hav to wrote C program that makes that... so i use fork() to create one process that executes ps aux --sort user... and then i want with another process to control the print of the processes and users... sry, if i explain my problem rong.

The command that i want to run is like this: ps aux --sort user | sort_by_user... this option sort_by_user doesn.t exists.. Make some process in C to run that command is simple with the commands fork() and execlp(), but create some option to that command in C i don´t hav any ideas.

Answer 5

You have a number of options depending on how much of it you want to do in C.

The simplest is to use system() to run a shell command (such as the one I posted earlier) to do the whole lot. system() will actually spawn a shell, so things like redirection will all work just as they do from the command line.

If you want to avoid using system() you could do it yourself, spawning two processes and linking them together. Look up pipe() and dup2(). Probably a waste of time.

You can run the ps program and parse its output in C. Again pipe() and dup2() are relevant. For the actual parsing, I'd just do it using the normal C string handling routines, as it's really quite straightforward. Obviously you could use a regex library instead but I think in this case it would result in more complicated code than without it.

Of course, you could do the whole lot in C by looking at files in /proc.

Answer 6

Use popen and manipulate the redirected stdout string in your C program

Answer 7

is this homework?

Answer 8

yep... i already solv the problem... redirect the stdout put and edit it... thx

Answer 9

viva a informatica no Dei. S.O é dificil!!

Answer 10

looool... moura