execvp("tail -1f /var/log/apache/www.cs.umu.se/access_log", args) ;

ylvawandel · 10-22-2005, 06:06 AM

Hello,

This code only gives the "ls" output.
Although running the command "tail -1f /var/log/apache/www.cs.umu.se/access_log"
directly in UNIX it is working, ie it's printing out
the logglines from that webserver...

Please Help!!

Code:

#include <stdio.h>
#include <stropts.h>
#include <poll.h>
#include <unistd.h>


int main(void)
{
	char *args[] = {"tail -1f /var/log/apache/www.cs.umu.se/access_log", NULL};
	execvp("tail -1f /var/log/apache/www.cs.umu.se/access_log", args) ;
	execvp("ls", args) ;

}

KrY

**Salem** · 10-22-2005, 06:21 AM

So why not just write a shell script?

The only reason it does "ls" is because your tail execl call fails miserably with an error. If it succeeded, you would not see the "ls" at all. execl level functions are one-way trips, if they succeed in running a new program they do not return.

Moved to linux forum

jim mcnamara · 10-24-2005, 01:32 PM

If you have to use "tail" try popen():

Code:

#include <stdio.h>
int main(void)
{
    FILE *fp=popen("tail -1f /var/log/apache/www.cs.umu.se/access_log", "r");
    char tmp[256]={0x0};
  
    while(fgets(tmp, sizeof(tmp), fp)!=NULL
    {
        fprintf(stdout,"%s",  tmp);
    }
    pclose(fp);
    return 0;
}

It would be faster to use fseek to get to the end of the log file, back pedal to the start of the last record, read it, print it. All in C.

10-22-2005, 06:06 AM	#1
ylvawandel Registered User Join Date: Oct 2005 Posts: 4	execvp("tail -1f /var/log/apache/www.cs.umu.se/access_log", args) ; Hello, This code only gives the "ls" output. Although running the command "tail -1f /var/log/apache/www.cs.umu.se/access_log" directly in UNIX it is working, ie it's printing out the logglines from that webserver... Please Help!! Code: #include <stdio.h> #include <stropts.h> #include <poll.h> #include <unistd.h> int main(void) { char *args[] = {"tail -1f /var/log/apache/www.cs.umu.se/access_log", NULL}; execvp("tail -1f /var/log/apache/www.cs.umu.se/access_log", args) ; execvp("ls", args) ; } KrY
ylvawandel is offline

10-22-2005, 06:21 AM	#2
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,710	So why not just write a shell script? The only reason it does "ls" is because your tail execl call fails miserably with an error. If it succeeded, you would not see the "ls" at all. execl level functions are one-way trips, if they succeed in running a new program they do not return. Moved to linux forum __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

10-24-2005, 01:32 PM	#3
jim mcnamara . Join Date: Nov 2003 Posts: 293	If you have to use "tail" try popen(): Code: #include <stdio.h> int main(void) { FILE *fp=popen("tail -1f /var/log/apache/www.cs.umu.se/access_log", "r"); char tmp[256]={0x0}; while(fgets(tmp, sizeof(tmp), fp)!=NULL { fprintf(stdout,"%s", tmp); } pclose(fp); return 0; } It would be faster to use fseek to get to the end of the log file, back pedal to the start of the last record, read it, print it. All in C.
jim mcnamara is offline

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