Thread: C system(...) function

Hello, everybody!

Here's a part of the code from a program I'm trying to do:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void main (int argc, char* argv[]) {

.....

system("clear");
system("rm something");
system("cp something_else something");

.....
.....
.....

system("source something");

}

Now why on Earth doesn't the source command work? It works perfectly when I write it in the console. The other commands I gave using system() (clear, rm and cp) worked just fine. But when I try it through a system function I get:

sh: source: not found

And I've tried this even after I gave the bash command (to be sure I'm in bash).

I've also tried the . (dot) version but it gives me an error too. The file I need to source to is a simple plain text file without any extension to the name (as I said source <that_file> works fine in console.

Note: I'm doing this on Ubuntu and compiling with gcc -o test test.c

Thank you in advance,

Adrian Chitan

Originally Posted by achitan

First thank you for responding so quickly. Your idea about /bash/sh before executing the system() command may be the winner. I have to check that.

The thing to remember is that changes made through one call of system() (eg through the source command) don't typically persist through subsequent calls.

You would probably be better off writing the set of commands you want to execute to a script file of the form;

Code:

#!/bin/bash

clear
rm something
cp something_else something

.....
.....
.....

source something

and then use a single system() call to execute that script file (which will work if bash is installed, and the script file is executable).

If need be, your program might create the script file immediately before executing it.

It might also be worth investigating functions that allow you to perform the required actions directly in code (without relying on a script or a shell that may or may not be installed, let alone working correctly).

source is a built-in function of some shells, but not others. IIRC, it is supported by csh and bash, but not by sh (which, under unix, is the default shell executed by the system() function).

Yes, this is a unix problem, not a C problem.

And, no, it's not weird at all. What you are seeing is how the shells work and interact with the system() function.

The source command (if supported by the current shell) executes a script in the context of the current shell.

The problem is that each system() call starts a different process for the shell (sh) and things done in one system() call (eg path settings) don't stick in the next system() call.

As I mentioned in a previous post, either include all the commands needed in a single script file (so all commands are executed by the same shell process) or work out a way to achieve the same results in code, without using the system() function.

If you have an executable script file then, by convention, a comment on the first line of the form "#!/bin/bash" means that script will be executed using /bin/bash

Given a command, the call: system("/bin/bash command"); will use bash to execute the command. However, when the system() call returns to the caller, the sh shell (invoked by system()) and the bash shell (which will be invoked by sh) processes will terminate. So, if you're relying on shell settings (eg path settings) to survive between system() calls - you will be disappointed.

Executing "source" via a system() call will never work, regardless of whether it's a shell built-in or not. System() launches a shell which then changes its own environment, then exits, essentially doing a no-op. To influence your program's environment you have to use setenv() directly.