topic Re: Can we execute more than one command with popen() ? in Operating System - Linux

Can we execute more than one command with popen() ?

Masthan — Mon, 03 Mar 2008 06:51:03 GMT

Hi All,
Can we execute more than one command by using popen() call?

I am gettign an error message When I try to execute the following command

popen("cd /sys/class/scsi_host/host0/device/../driver; pwd", "r").

I am seeing the following error message:

cd: /sys/class/scsi_host/host0/device/../driver: No such file or directory

actually the above command is succesfully executed @ shell prompt but when i try to execute the same command in .c file i am getting the above error.

Can any one debug this?

Your help is appreciated.

Regards
Masthan D

Re: Can we execute more than one command with popen() ?

Mark Grant — Mon, 03 Mar 2008 07:30:27 GMT

Any particular reason you don't just chdir() before your popen()?

However, the error you are getting suggests to me that the shell can't find your directory, not that popen() is failing.

popen() simply passes the string to "/bin/sh" and connects it's standard input and output accordingly. If the shell returns what you want then you should be able to read it through popen().

I just tried your "cd ...;pwd" string and it works fine.

Regards

Re: Can we execute more than one command with popen() ?

Masthan — Mon, 03 Mar 2008 07:33:33 GMT

Hi Mark,

Thanks for quick reply.

Can you try the following command on your linux machine?

popen("cd /sys/class/scsi_host/host0/device/../driver; pwd", "r");

FYI: I am using SLES 10 machine.

Regards
Masthan

Re: Can we execute more than one command with popen() ?

Mark Grant — Mon, 03 Mar 2008 07:37:52 GMT

Cool, I get the same error as you when I use that directory.

I'll have a little play now!

Re: Can we execute more than one command with popen() ?

Mark Grant — Mon, 03 Mar 2008 07:41:34 GMT

You'll notice this isn't a "popen" problem.

See the difference in these two commands.

sh -c "cd /tmp"

and

sh -c "cd /sys/class/scsi_host/host0/device/../driver"

It should be remembered that /sys isn't a real filesystem as such as is merely an export from the kernel. This almost certainly has something to do with it but it certainly requires further investigation.

Re: Can we execute more than one command with popen() ?

Mark Grant — Mon, 03 Mar 2008 07:46:59 GMT

Sorry to start spamming here!

Actually I think it's a combination of symbolic links and the sysfs filesystem. If you chdir() before popen() it works but you find yourself in the target directory not the symbolic link as such.

IS there another way you can get what you are trying to achieve?