sadashiv30 February 2016

Why does not os.system("cd mydir") work and we have to use os.chdir("mydir") instead in python?

I tried doing a "pwd" or cwd, after the cd, it does not seem to work when we use os.system("cd"). Is there something going on with the way the child processes are created. This is all under Linux.

Answers


Charles Duffy February 2016

os.system('cd foo') runs /bin/sh -c "cd foo"

This does work: It launches a new shell, changes that shell's current working directory into foo, and then allows that shell to exit when it reaches the end of the script it was called with.

However, if you want to change the directory of your current process, as opposed to the copy of /bin/sh that system() creates, you need that call to be run within that same process; hence, os.chdir().


David Schwartz February 2016

The system call creates a new process. If you do system("cd .., you are creating a new process that then changes its own current working directory and terminates. It would be quite surprising if a child process changing its current working directory magically changed its parent's current working directory. A system where that happened would be very hard to use.


Linuxios February 2016

os.system (which is just a thin wrapper around the POSIX system call) runs the command in a shell launched as a child of the current process. Running a cd in that shell only changes the current directory of that process, not the parent.

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