Bash是否在我的python命令行参数中扩展了“ *”字符？

Question

With the following command in bash :

python myscript.py filename_pattern*

I got two different sys.argv in two Linux machines:

• Machine A : sys.argv[1] = filename_pattern*
• Machine B : sys.argv[1] = filename_pattern-2013-06-30

Note : filename_pattern-2013-06-30 is a file in my current directory.

One of my colleague tell me that's the evil of bash . But I check the bash in two machines are of the same version, and I checked ~/.bashrc , /etc/bashrc , /etc/profile.d/*.sh too.

Can anyone point out how come the two same version bash act differently ?

Answer 1

It is because in one of your machine, in the folder, there in no file that could match the pattern. So when this happens, the * remains. You can test with one computer, with and without a file match the pattern. There is another reason, the shell option nullglob is disabled. You can read the GNU bash reference for this.

Answer 2

Why you see the different behavior on the two machines is either down to the files present in the directory on both machines or based on the shell options, as pointed out in the comments.

Either way, the way to avoid the problem is to simply surround the argument in quotes so that Bash treats it literally.

python myscript.py "filename_pattern*"

Answer 3

You could handle it in your python program like this example that I found in an introductory book on python. Then it won't matter if bash expands it or not.

import glob
import sys

sys.argv = [item for arg in sys.argv for item in glob.glob(arg)]