You can execute the command in a subshell using os.system(). This will call the Standard C function system(). This function will return the exit status of the process or command. This method is considered as old and not recommended, but presented here for historical reasons only. The subprocess module is recommended and it provides more powerful facilities for running command and retrieving their results.
os.system example (deprecated)
The syntax is:
import os os.system("command") |
In this example, execute the date command:
import os os.system("date") |
Sample outputs:
Sat Nov 10 00:49:23 IST 2012 0
In this example, execute the date command using os.popen() and store its output to the variable called now:
import os f = os.popen('date') now = f.read() print "Today is ", now |
Sample outputs:
Today is Sat Nov 10 00:49:23 IST 2012
Say hello to subprocess
The os.system has many problems and subprocess is a much better way to executing unix command. The syntax is:
import subprocess subprocess.call("command1") subprocess.call(["command1", "arg1", "arg2"]) |
In this example, execute the date command:
import subprocess subprocess.call("date") |
Sample outputs:
Sat Nov 10 00:59:42 IST 2012 0
You can pass the argument using the following syntax i.e run ls -l /etc/resolv.conf command:
import subprocess subprocess.call(["ls", "-l", "/etc/resolv.conf"]) |
Sample outputs:
<-rw-r--r-- 1 root root 157 Nov 7 15:06 /etc/resolv.conf 0
To store output to the output variable, run:
import subprocess p = subprocess.Popen("date", stdout=subprocess.PIPE, shell=True) (output, err) = p.communicate() print "Today is", output |
Sample outputs:
Today is Sat Nov 10 01:27:52 IST 2012
Another example (passing command line args):
import subprocess p = subprocess.Popen(["ls", "-l", "/etc/resolv.conf"], stdout=subprocess.PIPE) output, err = p.communicate() print "*** Running ls -l command ***\n", output |
Sample outputs:
*** Running ls -l command *** -rw-r--r-- 1 root root 157 Nov 7 15:06 /etc/resolv.conf
In this example, run ping command and display back its output:
import subprocess p = subprocess.Popen(["ping", "-c", "10", "www.cyberciti.biz"], stdout=subprocess.PIPE) output, err = p.communicate() print output |
The only problem with above code is that output, err = p.communicate() will block next statement till ping is completed i.e. you will not get real time output from the ping command. So you can use the following code to get real time output:
import subprocess cmdping = "ping -c4 www.cyberciti.biz" p = subprocess.Popen(cmdping, shell=True, stderr=subprocess.PIPE) while True: out = p.stderr.read(1) if out == '' and p.poll() != None: break if out != '': sys.stdout.write(out) sys.stdout.flush() |
Sample outputs:
PING www.cyberciti.biz (75.126.153.206) 56(84) bytes of data. 64 bytes from www.cyberciti.biz (75.126.153.206): icmp_req=1 ttl=55 time=307 ms 64 bytes from www.cyberciti.biz (75.126.153.206): icmp_req=2 ttl=55 time=307 ms 64 bytes from www.cyberciti.biz (75.126.153.206): icmp_req=3 ttl=55 time=308 ms 64 bytes from www.cyberciti.biz (75.126.153.206): icmp_req=4 ttl=55 time=307 ms --- www.cyberciti.biz ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3001ms rtt min/avg/max/mdev = 307.280/307.613/308.264/0.783 ms |
Related media
A quick video demo of above python code:
HTML 5 Video 01: Python Run External Command And Get Output On Screen or In Variable
References:
- Python 2.x: subprocess documentation.
- Python 3.x: subprocess documentation.
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307 ms?
That’s a long interval ;)
Hi, please more small and usefull examples with python like it! more code snippets!
A very comprehensive explanation, being useful to beginners to python.
where to find the command of linux
these commands are very helpfull us….please give more example like this.
Thanks!
What exactly does Shell=True does?
please tell the exact usage of the shell argumet.
Hi,
First off, enjoy all your posts and youtube videos. Recently viewed your tutorial on installing freebsd. So thank you for sharing your knowledge.
I have a query regarding launching an external bash script file (.sh) in freebsd.
For linux I used:
os.system(‘sh ‘ + filepath)
For Mac:
os.system(‘open ‘ + filepath)
And for windows:
os.startfile(filepath)
I am unable to get any of these to work for freebsd. I know startfile is only for windows, however was wondering if there was an equivalent for freebsd without using subprocess. Or if not possible at all how to use subprocess to call a external script.
Also, in freebsd, what would be the equivalent of say:
sudo chown -R user:user file.bundle
as both sudo and chown are not installed by default.
Any help would be appreciated.
Regards,
iSh0w
tnxxxxxxx
What if I want to create a variable in Python, then pass that variable to a bash command line?
Something like this:
….
celsius = sensor.read_temperature()
import subprocess
subprocess.call([“myscript.sh”, “-v”, “-t $celsius”])
Is that possible?
Of course you can. In python’s new formatting it would look like this:
subprocess.call(["myscript.sh", "-v", "-t {}".format(celsius)])I use split so I dont have to write literal arrays. Works most of the time.
I also find `”my command goes here”.split()` easier to use and maintain. To get proper handling of quoted args, use shlex.split: `shlex.split(”’this is my “quoted string” argument”’)`, which gives `[‘this’, ‘is’, ‘my’, ‘quoted string’, ‘argument’]`