script in c

script in c

[kaushal]

Hello  all,
           Is there a way by which I can exec a shell script without
using the "system()" call?
Thanks in advance.
 
cheers-
kaushal.

RE: script in c

[Honnavalli_Sreevathsa]

You can use popen() and pclose() calls


> -----Original Message-----
> From: linux-c-programming-owner@vger.kernel.org 
> [mailto:linux-c-programming-owner@vger.kernel.org] On Behalf 
> Of kaushal
> Sent: Monday, November 08, 2004 11:09 AM
> To: linux prg
> Subject: script in c
> 
> 
> Hello  all,
>            Is there a way by which I can exec a shell script 
> without using the "system()" call? Thanks in advance.
>  
> cheers-
> kaushal.
> 
> -
> To unsubscribe from this list: send the line "unsubscribe 
> linux-c-programming" in the body of a message to 
> majordomo@vger.kernel.org More majordomo info at  
http://vger.kernel.org/majordomo-info.html

Re: script in c

[Ron Michael Khu]

or the exec functions =)

Honnavalli_Sreevathsa@emc.com wrote:

>You can use popen() and pclose() calls
>
>
>  
>
>>-----Original Message-----
>>From: linux-c-programming-owner@vger.kernel.org 
>>[mailto:linux-c-programming-owner@vger.kernel.org] On Behalf 
>>Of kaushal
>>Sent: Monday, November 08, 2004 11:09 AM
>>To: linux prg
>>Subject: script in c
>>
>>
>>Hello  all,
>>           Is there a way by which I can exec a shell script 
>>without using the "system()" call? Thanks in advance.
>> 
>>cheers-
>>kaushal.
>>
>>-
>>To unsubscribe from this list: send the line "unsubscribe 
>>linux-c-programming" in the body of a message to 
>>majordomo@vger.kernel.org More majordomo info at  
>>    
>>
>http://vger.kernel.org/majordomo-info.html
>-
>To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
>the body of a message to majordomo@vger.kernel.org
>More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
>  
>

Re: script in c

[Jan-Benedict Glaw]

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On Mon, 2004-11-08 14:32:25 +0800, Ron Michael Khu <ronkhu@ntsp.nec.co.jp>
wrote in message <418F12F9.6070701@hq.ntsp.nec.co.jp>:

[Calling a script from within a C program]

> or the exec functions =)

Which is generally preferred over system().  system() is a horrible
mess: you face a hard time to properly supply command line arguments
(think about arguments with tabs, spaces, CR or LF in them...).

Just always use the exec functions.

MfG, JBG

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Re: script in c

[linux-c-programming-owner]

--- kaushal <kaushal@rocsys.com> wrote:

> Hello  all,

Hello,

>            Is there a way by which I can exec a
> shell script without
> using the "system()" call?
> Thanks in advance.

You can use exec*() family for this purpose.

man exec

Here is a little sample:

[mbaris@zion:/tmp/code_temp]$ cat exec.c
#include <unistd.h>
#include <string.h>
#include <errno.h>

int main(void)
{
  if (execl("/bin/sh", "-c", "./script.sh", NULL)==-1)
  {
    printf("ERROR: %s\n", strerror(errno));
  }

  return 0;
}


[mbaris@zion:/tmp/code_temp]$ cat script.sh
#!/bin/bash

echo "Fired!";
exit;

[mbaris@zion:/tmp/code_temp]$ gcc -o exec exec.c
[mbaris@zion:/tmp/code_temp]$ ./exec
Fired!
[mbaris@zion:/tmp/code_temp]$

>  
> cheers-
> kaushal.
> 


=====
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spontaneous system crashes, usually just before saving a massive project. Easily cured by UNIX.  See also MS-DOS, IBM-DOS, DR-DOS.


		
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Re: script in c

[Glynn Clements]

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> >            Is there a way by which I can exec a
> > shell script without
> > using the "system()" call?
> > Thanks in advance.
> 
> You can use exec*() family for this purpose.
> 
> man exec
> 
> Here is a little sample:
> 
> [mbaris@zion:/tmp/code_temp]$ cat exec.c
> #include <unistd.h>
> #include <string.h>
> #include <errno.h>
> 
> int main(void)
> {
>   if (execl("/bin/sh", "-c", "./script.sh", NULL)==-1)
>   {
>     printf("ERROR: %s\n", strerror(errno));
>   }
> 
>   return 0;
> }

A system() replacement is somewhat more complex than that.

If the process wants to continue executing after the script has
finished, you need to fork() a child process, have the child perform
the exec(), then wait() for the child to finish. You may also need to
change the signal handling while the child is executing (system()
ignores SIGINT and SIGQUIT and blocks SIGCHLD while the child process
runs).

A more complete example is attached.

-- 
Glynn Clements <glynn@gclements.plus.com>


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#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>

int spawn(char *command, char **args)
{
	/* sample usage:
	 *	
	 *	char *args[3];
	 *	
	 *	args[0] = "sh";
	 *	args[1] = "/path/to/script";
	 *	args[2] = NULL;
	 *	spawn("/bin/sh", args);
	 */

	struct sigaction act, intr, quit;
	sigset_t block, oldmask;
	int status = -1;
	pid_t pid;

	sigemptyset(&act.sa_mask);
	act.sa_flags = SA_RESTART;

	act.sa_handler = SIG_IGN;
	if (sigaction(SIGINT, &act, &intr) < 0)
		goto error_1;
	if (sigaction(SIGQUIT, &act, &quit) < 0)
		goto error_2;

	sigemptyset(&block);
	sigaddset(&block, SIGCHLD);
	if (sigprocmask(SIG_BLOCK, &block, &oldmask) < 0)
		goto error_3;

	pid = fork();

	if (pid < 0)
	{
		fprintf(stderr, "unable to create a new process");
		goto error_4;
	}

	if (pid == 0)
	{
		sigaction(SIGINT, &intr, NULL);
		sigaction(SIGQUIT, &quit, NULL);

		execvp(command, args);
		/* if we reach this point, execvp() failed */
		fprintf(stderr, "unable to execute command");
		_exit(127);
	}
	else
	{
		pid_t n;

		do n = waitpid(pid, &status, 0);
		while (n == (pid_t) -1 && errno == EINTR);

		if (n != pid)
			status = -1;
	}

error_4:
	sigprocmask(SIG_SETMASK, &oldmask, NULL);
error_3:
	sigaction(SIGQUIT, &quit, NULL);
error_2:
	sigaction(SIGINT, &intr, NULL);
error_1:
	return status;
}