Question

I have a need, for a python script I’m creating, to first get just the PID of a process (based on its name) and then to get from that process, usings its PID, its time duration, which, from the printout below, would be “00:00:00”

root      5686     1  0 Sep23 ?        00:00:00 process-name

I am using this to get just the PID, by the process’s name:

ps -ef |grep `whoami`| grep process-name | cut -c10-15

So, this works fine and I am assuming that the cut parameters (-c10-15) would work universally as the placement of the PID shouldn’t change (I just got this from a snippet I found)

However, when I try to do something similar to get just the TIME value, such as this it returns it differently

ps -f 5686

returns:

root      5686     1  0 Sep23 ?        S      0:00 /path/to/process

So when I try a cut, as below, I don’t think it would work properly as I’m not sure the spacing on this return is consistent and also its showing the time value differently than before (not the original “00:00:00” style of printout.

ps -f 5686 | cut -c40-47

I’m using this in my python script to record the PID of a specific process type (by name) so that I can later shut down that instance of the progra when needed. Any advice on what I can do to correct my approach is appreciated

Answer 1

Use the -o option to control what data is output and in what order.

e.g.

$ ps -o pid,time,comm
  PID     TIME COMMAND
 3029 00:00:01 zsh
22046 00:00:00 ps

or

$ ps -o pid,time,comm --no-headers
 3029 00:00:01 zsh
22046 00:00:00 ps

This will make it easier to parse. I would suggest parsing the output with python using (pid, time, cmd) = result.split(2)

Alternatively use the pgrep command to only list processes that match given criteria.