How to get only the user, the pid and the command run for a specific process? (Ubuntu 11.10)

I guess you are looking for the -o argument:

-o format:

user-defined format. format is a single argument in the form of a blank-separated or comma-separated list, which offers a way to specify individual output columns. The recognized keywords are described in the STANDARD FORMAT SPECIFIERS section below. Headers may be renamed (ps -o pid,ruser=RealUser -o comm=Command) as desired. If all column headers are empty (ps -o pid= -o comm=) then the header line will not be output. Column width will increase as needed for wide headers; this may be used to widen up columns such as WCHAN (ps -o pid,wchan=WIDE-WCHAN-COLUMN -o comm). Explicit width control (ps opid,wchan:42,cmd) is offered too. The behavior of ps -o pid=X,comm=Y varies with personality; output may be one column named "X,comm=Y" or two columns named "X" and "Y". Use multiple -o options when in doubt. Use the PS_FORMAT environment variable to specify a default as desired; DefSysV and DefBSD are macros that may be used to choose the default UNIX or BSD columns.

So the command you want would be (Ubuntu):

ps -o uid,pid,cmd -ef|grep python

under OpenSolaris the command is:

ps -o ruser,pid,comm -ef|grep python

The simplest would probably be:

$ ps o uid=,pid=,cmd= -C python
1000 26126 python

That way you get everything directly from ps and don't need to parse anything.

From the ps man page:

-o format

User-defined format. format is a single argument in the form of a blank-separated or comma-separated list, which offers a way to specify individual output columns. [...] Headers may be renamed (ps -o pid,ruser=RealUser -o comm=Command) as desired. If all column headers are empty (ps -o pid= -o comm=) then the header line will not be output.

-C cmdlist
     Select by command name.  This selects the processes whose executable 
     name is given in cmdlist.

The -C option will work if you are running python interactively, not if python is running a script. In that case you should use -C scriptname.py instead.

ps -eo user,pid,cmd | grep [p]ython

Example:

$ ps -eo user,pid,cmd | grep [p]ython
root      1056 /usr/bin/python3 /usr/bin/networkd-dispatcher --run-startup-triggers
root      1735 /usr/bin/python3 /usr/bin/fail2ban-server -xf start
user     16613 /usr/bin/python3 /usr/share/system-config-printer/applet.py

Explanation:

• -e all processes
• -o user-defined format
• user,pid,cmd Show user, process ID, command columns

Note: if you use -f with -o as others have suggested, you may get errors. This is because both of these parameters control the output format, and only one of them should be used:

$ ps --help | grep -A 2 "output format"
*********** output format **********
-o,o user-defined  -f full
-j,j job control   s  signal