CODEWITHSUNDEEP
clinuxunix
Tombart
Tombart

Reputation: 32408

How to read all environment variables of a single process using C?

openproc provides API for retrieving data from /proc. But all examples I found read data about all processes. With PROC_FILLENV it should allocate environment variables:

allocate environ part of proc_t and read information from /proc/#pid/environ

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <proc/readproc.h>

int main(){
  PROCTAB* proc = openproc(PROC_FILLENV);
  proc_t proc_info;

  memset(&proc_info, 0, sizeof(proc_info));
  while (readproc(proc, &proc_info) != NULL) {
    printf("%s\n", *proc_info.environ);
  }

  closeproc(proc);
}

But it still reads information about all processes. How can I filter processes by PID?

Upvotes: 1

Views: 476

Answers (1)

Tombart
Tombart

Reputation: 32408

PROC_PID flag and list of PIDs are needed as 2nd argument:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <proc/readproc.h>

// compile with:
// gcc environ.c -lprocps -o bin/environ
int main(){
  pid_t* pidList= NULL;

  pidList = (pid_t*) malloc(sizeof(pid_t)*2 );

  // lookup only processes whose pid is contained in pidlist
  pidList[0] = 1234;
  pidList[1] = 0; // the list is terminated with 0

  PROCTAB* proc = openproc(PROC_PID | PROC_FILLENV, pidList);
  proc_t proc_info;

  memset(&proc_info, 0, sizeof(proc_info));
  while (readproc(proc, &proc_info) != NULL) {
    int i = 0;
    //environ is an array of *char
    while(proc_info.environ[i] != NULL) {
      printf("%s\n", proc_info.environ[i++]);
    }
  }
  closeproc(proc);
  free(pidList);
}

Upvotes: 1

Related Questions