Core Python Programming (2nd Edition)

from the interactive interpreter so that you can observe how system() works.
>>> import os
>>> result = os.system('cat /etc/motd')
Have a lot of fun...
>>> result
0
>>> result = os.system('uname -a')
Linux solo 2.2.13 #1 Mon Nov 8 15:08:22 CET 1999 i586 unknown
>>> result
0
You will notice the output of both commands as well as the exit status of their execution, which we
saved in the result variable. Here is an example executing a DOS command:
>>> import os
>>> result = os.system('dir')
Volume in drive C has no label
Volume Serial Number is 43D1-6C8A
Directory of C:\WINDOWS\TEMP
. 01-08-98 8:39a .
.. 01-08-98 8:39a ..
0 file(s) 0 bytes
2 dir(s) 572,588,032 bytes free
>>> result
0
14.5.2. os.popen()
The popen() function is a combination of a file object and the system() function. It works in the same
way as system() does, but in addition, it has the ability to establish a one-way connection to that
program and then to access it like a file. If the program requires input, then you would call popen() with
a mode of 'w' to "write" to that command. The data that you send to the program will then be received
through its standard input. Likewise, a mode of 'r' will allow you to spawn a command, then as it writes
to standard output, you can read that through your file-like handle using the familiar read*() methods of
file object. And just like for files, you will be a good citizen and close() the connection when you are
finished.
In one of the system() examples we used above, we called the Unix uname program to give us some
information about the machine and operating system we are using. That command produced a line of
output that went directly to the screen. If we wanted to read that string into a variable and perform
internal manipulation or store that string to a log file, we could, using popen(). In fact, the code would
look like the following:
>>> import os
>>> f = os.popen('uname -a')
>>> data = f.readline()
>>> f.close()
>>> print data,
Linux solo 2.2.13 #1 Mon Nov 8 15:08:22 CET 1999 i586 unknown