I need to make some command line calls to linux and get the return from this, however doing it as below is just returning 0 when it should return a time value, like 00:08:19, I am testing the exact same call in regular command line and it returns the time value 00:08:19 so I am confused as to what I am doing wrong as I thought this was how to do it in python.
import os
retvalue = os.system("ps -p 2993 -o time --no-headers")
print retvalue
What gets returned is the return value of executing this command. What you see in while executing it directly is the output of the command in stdout. That 0 is returned means, there was no error in execution.
Use popen etc for capturing the output .
Some thing along this line:
import subprocess as sub
p = sub.Popen(['your command', 'arg1', 'arg2', ...],stdout=sub.PIPE,stderr=sub.PIPE)
output, errors = p.communicate()
print output
or
import os
p = os.popen('command',"r")
while 1:
line = p.readline()
if not line: break
print line
ON SO : Popen and python
If you're only interested in the output from the process, it's easiest to use subprocess' check_output function:
output = subprocess.check_output(["command", "arg1", "arg2"]);
Then output holds the program output to stdout. Check the link above for more info.
The simplest way is like this:
import os
retvalue = os.popen("ps -p 2993 -o time --no-headers").readlines()
print retvalue
This will be returned as a list
Your code returns 0 if the execution of the commands passed is successful and non zero if it fails. The following program works on python2.7, haven checked 3 and versions above. Try this code.
>>> import commands
>>> ret = commands.getoutput("ps -p 2993 -o time --no-headers")
>>> print ret
Yes it's counter-intuitive and does not seem very pythonic, but it actually just mimics the unix API design, where these calld are C POSIX functions. Check man 3 popen && man 3 system
Somewhat more convenient snippet to replace os.system that I use:
from subprocess import (PIPE, Popen)
def invoke(command):
'''
Invoke command as a new system process and return its output.
'''
return Popen(command, stdout=PIPE, shell=True).stdout.read()
result = invoke('echo Hi, bash!')
# Result contains standard output (as you expected it in the first place).
I can not add a comment to IonicBurger because I do not have "50 reputation" so I will add a new entry. My apologies. os.popen() is the best for multiple/complicated commands (my opinion) and also for getting the return value in addition to getting stdout like the following more complicated multiple commands:
import os
out = [ i.strip() for i in os.popen(r"ls *.py | grep -i '.*file' 2>/dev/null; echo $? ").readlines()]
print " stdout: ", out[:-1]
print "returnValue: ", out[-1]
This will list all python files that have the word 'file' anywhere in their name. The [...] is a list comprehension to remove (strip) the newline character from each entry. The echo $? is a shell command to show the return status of the last command executed which will be the grep command and the last item of the list in this example. the 2>/dev/null says to print the stderr of the grep command to /dev/null so it does not show up in the output. The 'r' before the 'ls' command is to use the raw string so the shell will not interpret metacharacters like '*' incorrectly. This works in python 2.7. Here is the sample output:
stdout: ['fileFilter.py', 'fileProcess.py', 'file_access..py', 'myfile.py']
returnValue: 0
This is an old thread, but purely using os.system, the following's a valid way of accessing the data returned by the ps call. Note: it does use a pipe to write the data to a file on disk. And OP didn't specifically ask for a solution using os.system.
>>> os.system("ps > ~/Documents/ps.txt")
0 #system call is processed.
>>> os.system("cat ~/Documents/ps.txt")
PID TTY TIME CMD
9927 pts/0 00:00:00 bash
10063 pts/0 00:00:00 python
12654 pts/0 00:00:00 sh
12655 pts/0 00:00:00 ps
0
accordingly,
>>> os.system("ps -p 10063 -o time --no-headers > ~/Documents/ps.txt")
0
>>> os.system("cat ~/Documents/ps.txt")
00:00:00
0
No idea why they are all returning zeroes though.
For your requirement, Popen function of subprocess python module is the answer. For example,
import subprocess
..
process = subprocess.Popen("ps -p 2993 -o time --no-headers", stdout=subprocess.PIPE, stderr=subprocess.PIPE)
stdout, stderr = process.communicate()
print stdout
okey I believe the fastest way it would be
import os
print(os.popen('command').readline())
x = _
print(x)
using commands module
import commands
"""
Get high load process details
"""
result = commands.getoutput("ps aux | sort -nrk 3,3 | head -n 1")
print result -- python 2x
print (result) -- python 3x
