Michael Williams wrote:
Hi All,
I've recently seen the "subprocess" module and am rather confused by
it's requirements. Is it not possible to execute an entire string
without having to break them up into a list of arguments? For
instance, I'd much rather do the following:
subprocess.call("ls -al | grep -i test")
. . .than to have to:
list = ["ls", "-a", "-l" ] . . . . . . and so on and so forth.
subprocess.call(list. . .)
What is the best way to go about executing a massively complex single
line command?
Thanks,
Michael
How about a hybrid solution?:
from subprocess import Popen, PIPE
from string import strip
(stdout, stderr) = Popen(['ls','-al'], stdout=PIPE,
stderr=PIPE).communicate()
/# process spins off. Ideally, you should wait for it to complete,
or assign the resulting object of Popen
# to a variable and inquire if it's completed via the 'poll()'
operator or wait on it via the 'wait()'
# operator.
# then query the stderr via communicate()[1]; if good, i.e.
len(stderr) == 0, inspect the resulting
# stdout string (via communicate()[0]) for your 'test' result. But
I'm being lazy. I assume the call to
# ls -al will be faster then my next statement./
res = []
for line in stdout.strip():
if 'test' in line:
res.append( line )
Do the work you need done at the shell prompt, do the rest in Python.
Also I wonder if, you were looking for the word 'test' in the filename,
glob.glob wouldn't have been a bit more efficient? But if you were
looking for a 'test' owner or group then using:
glob.glob(): get the _list_ of files, with directory. Example:
*glob.glob('/bin/*') *
os.stat(): get an _object_ of stats on a file. Example:*
os.stat('/bin/ls')*
stat.ST_UID: get just the group id, as an _integer_ from the object
returned by os.stat. Example: *os.stat('/bin/ls')[stat.ST_UID]
*pwd.getpwgid(): get the _string_ translation of a UID. Example:
*pwd.getpwgid( os.stat('/bin/ls')[stat.ST_UID] )*
stat.ST_GID: get the group id, as an _integer_ from the object
returned os.stat. Example:
*os.stat('/bin/ls')[stat.ST_GID]*
grp.getgrgid(): get the _string_ translation of a UID. Example:
*grp.getgrgid( os.stat('/bin/ls')[stat.ST_UID] )*
Now I have a list, which I iterate over, getting the UID and GID, as
strings, that I can compare to. I never had to use a subprocess and
having to build up a 'wait on done loop'. Note, grp and pwd, I think,
are Python/Unix functions. What one does on Windows I don't know, but
I'll bet there are similar functions under Python/Windows. Don't get me
wrong, Subprocess is a fast and damn useful tool. I often use it to
verify a program is in my path, before creating a subprocess to run some
task python isn't built for (like mencoder functionality).
You see, the issue is: _shell,_ _python & shell_ or _python alone_. When
transitioning from one language to another, say C/C++/Java to Python, it
is often easier to use your knowledge of the shell command (bash/Bourne
for example) to get things done. But it's only a transitional issue. The
need to use the shell is a good demonstrator that either the Interpretor
is weak, or that you haven't fully explored it's abilities. With the
Python Interpretor at v2.4 going onto v2.5, it's very likely that the
desired feature exists; you have but to do some clever research to find
it. As to clever research ... I find Google a good place to start.
I had some familiarity with os.stat and glob. But the grp and pwd
functions were things I discovered from
http://docs.python.org/modindex.html and about two minutes of searching
for 'python uid to name' @ Google.
Also, os.listdir and os.path.join would have worked just as well as
glob.glob('dirname/*'). But glob.glob was faster to write. Even a better
choice would have been to use the 'os.walk' to iterate over the
directory tree.
sph.
--
HEX: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
--
http://mail.python.org/mailman/listinfo/python-list
