Linux环境编程

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{
  char *var, *value;
  if (argc == 1 || argc >3)
  {
    fprintf(stderr, "usage: environ var[value]\n");
    exit(1);
  }
  var = argv[1];
  value = getenv(var);
  if (value)
  {
    printf("Variable %s has value %s\n",var, value);
  }
  else
  {
    printf("Variable %s has no value\n",var);
  }
  if (argc == 3)
  {
    char *string;
    value = argv[2];
    string = malloc(strlen(var) + strlen(value + 2));
    if (!string)
    {
      fprintf(stderr,"out of memory!\n");
      exit(1);
    }
    strcpy(string,var);
    strcat(string,"=");
    strcat(string,value);
    printf("Calling putenv with: %s\n", string);
    if(putenv(string)!=0)
    {
      fprintf(stderr,"putenv failed\n");
      free(string);
      exit(1);
    }
    value = getenv(var);
    if (value)
    printf("New value of %s is %s\n",var,value);
    else
    printf("New value of %d is null ??\n",var);
  }
  exit(0);
}