Linux exercises (read and change environment variables)

#include <stdlib.h>#include <stdio.h>#include <string.h>int main(int argc,char **argv){        char *var,*value;        if(argc==1||argc>3)        {                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 memoryy\n");                        exit(1);                }                strcpy(string,var);                strcat(string,"=");                strcat(string,value);                printf("Calling putenv with: %s\n",string);                if(putenv(string)!=0)                {                        free(string);                        exit(1);                }                value=getenv(var);                if(value)                        printf("New value of %s is %s\n",var,value);                else                        printf("New value of %s is null??\n",var);        }        exit(0);}

Function prototype:

# Include <stdlib. h>

Char * getenv (const char * Name); if the environment variable does not exist, null is returned.

Int putenv (const char * string);-1 is returned if an environment variable fails to be added.