How to extract string froms system calls in c prog

[ZF]

Taken from:
crasseux.com/books/ctutorial/Programming-with-pipes.html

The following program example shows how to pipe the output of the ps -A command to the grep init command, exactly as in the GNU/Linux command line example above. The output of this program should be almost exactly the same as sample output shown above.

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

int
main ()
{
FILE *ps_pipe;
FILE *grep_pipe;

int bytes_read;
int nbytes = 100;
char *my_string;

/* Open our two pipes */
ps_pipe = popen ("ps -A", "r");
grep_pipe = popen ("grep init", "w");

/* Check that pipes are non-null, therefore open */
if ((!ps_pipe) || (!grep_pipe))
{
fprintf (stderr,
"One or both pipes failed.\n");
return EXIT_FAILURE;
}

/* Read from ps_pipe until two newlines */
my_string = (char *) malloc (nbytes + 1);
bytes_read = getdelim (&my_string, &nbytes, "\n\n", ps_pipe);

/* Close ps_pipe, checking for errors */
if (pclose (ps_pipe) != 0)
{
fprintf (stderr,
"Could not run 'ps', or other error.\n");
}

/* Send output of 'ps -A' to 'grep init', with two newlines */
fprintf (grep_pipe, "%s\n\n", my_string);

/* Close grep_pipe, cehcking for errors */
if (pclose (grep_pipe) != 0)
{
fprintf (stderr,
"Could not run 'grep', or other error.\n");
}

/* Exit! */
return 0;
}

[ZF]

To extract the fields, you can either use awk '{print $4}' or you can use strtok.


<source language="c++">
/* strtok example */
#include <stdio.h>
#include <string.h>

int main ()
{
char str[] ="- This, a sample string.";
char * pch;
printf ("Splitting string \"%s\" into tokens:\n",str);
pch = strtok (str," ,.-");
while (pch != NULL)
{
printf ("%s\n",pch);
pch = strtok (NULL, " ,.-");
}
return 0;
}
</source>