Question

My friend has an below assignment , can anyone can guide how to do this in “C”, just guidence is enough.

Write a program to store all processes list into a file and sort all the processes with UID.

For example:

./a.out processidlist.txt

it has to save the info to processidlist.txt.

In this processidlist.txt it has to sort the processes with UID.

he tried the below

ps –A –o UID > outputfile

Thanks

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

int main( int argc, char *argv[] )
{
  FILE *fp1, *fp2;
  FILE *fp;
  int status;
  char path[1035];

   fp1 = fopen( argv[1], "w" );
   if ( ! fp1 )
   {
      printf("Error opening file %s\n", argv[1]);
   }

  /* Open the command for reading. */
  fp = popen("ps -Af | sort -k1", "r");
  if (fp == NULL) {
    printf("Failed to run command\n" );
    exit;
  }

  /* Read the output a line at a time - output it. */
  while (fgets(path, sizeof(path)-1, fp) != NULL) {
    printf("%s", path);
    fputs( path, fp1 );
  }

  /* close */
  pclose(fp);
  fclose(fp1);
  return 0;
}

Answer 1

Something on these lines should work

system("ps -Af | sort -k1");

A indicates all processes
f generates full listing
k denotes sort by column
1 denotes first column which is UID of the processes

And if you don’t want the annoying header

UID        PID  PPID  C STIME TTY          TIME CMD

along with your processes list, then use sed to delete first line of ps output

system("ps -Af | sed "1 d" | sort -k1");