来自python内部的bash命令

Question

I'm looking for the best way to use bash commands from within python. What ways are there? I know of os.system and subprocess.Popen.

I have tried these:

bootfile = os.system("ls -l /jffs2/a.bin | cut -d '/' -f 4")
print bootfile

This returns a.bin as expected but also it retuns 0 afterwards and so prints:

a.bin
0

with bootfile now being set to 0. The next time I print bootfile it just shows up as 0. Which is the exit value I guess, how do i stop this value interfering?

I have also tried:

bootfile = subprocess.Popen("ls -l /jffs2/a.bin | cut -d '/' -f 4")
print bootfile

but it seems to break the script, as in I get nothing returned at all, have I done that right?

Also which of these is better and why? Are there other ways and what is the preferred way?

Answer 1

使用os.readlink （由@kojiro提出）和os.path.basename仅获取名称文件：

os.path.basename(os.readlink('/jffs2/a.bin'))

Answer 2

kojiro's comment about os.readlink is probably what you want. I am explaining what you were trying to implement.

os.system would return you exit status of the command run.

subprocess.Popen will create a pipe, so that you can capture the output of the command run.
Below line will capture output of the command run:

bootfile = subprocess.Popen(["bash","-c","ls -l /jffs2/a.bin | cut -d '/' -f 4"], stdout=subprocess.PIPE).communicate()[0]

More details at http://docs.python.org/library/subprocess.html

Answer 3

The right answer, as @kojiro says, is:

os.readlink('/jffs2/a.bin')

But if you really wanted to do this the complicated way, then in Python 2.7:

cmd = "ls -l /jffs2/a.bin | cut -d '/' -f 4"
bootfile = subprocess.check_output(cmd, shell=True)

Or on older Pythons:

cmd = "ls -l /jffs2/a.bin | cut -d '/' -f 4"
p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)
bootfile = p.communicate()[0]
if p.returncode != 0:
    raise Exception('It failed')