Question

I have a custom shell program in which I have included signal.h, unistd.h, and stdio.h. I was originally working on this in RedHat Enterprise (not sure exactly what version, but not too old) and I was able to use gcc on my program and it compiled fine and ran fine. Now I moved it over to Ubuntu and gcc is giving me some errors, the first of which is conflicting types for 'getline()'. Some other errors say incompatible implicit declaration of built-in function strlen. I have overridden the functions in question, why was this working in RedHat but not in Ubuntu? Linux is not my thing so please speak plainly. Let me know if you need more error details.

/* define a global input buffer */
#include <signal.h>
#include <unistd.h>
#include <stdio.h>

#define MAXARG 512
#define MAXBUF 512
#define BUFFER_SIZE 50
#define MAX_COMMANDS 10
char buffer [BUFFER_SIZE];
static char *prompt = "MYSHELL>";
static char inpbuf[MAXBUF];
static char *arg[MAXARG+1];
static char tokbuf[2*MAXBUF];
static char *tok = tokbuf;
char history[MAX_COMMANDS][MAXBUF];
int cmd_num;

void getline(void);

void getline() {
int length;

length = read(0, inpbuf, MAXBUF);
if (length == 0) {
    printf("\n");
    exit(0);
}
inpbuf[length] = '\0';

}

void processline() {
char *ptr = inpbuf;
int narg;
for (narg=0;;) {    
    arg[narg] = tok;
    for (; *ptr == ' ' || *ptr == '\t'; ptr++)
        ;
    while(*ptr != ' ' && *ptr != '\t' && *ptr != '\n' && 
          *ptr != '\0' && *ptr != ';' && *ptr != '&') 
        *tok++ = *ptr++;
    *tok++ = '\0';
    if (narg < MAXARG)
        narg++;
    if (*ptr == '\n')
        break;
}
// clear the input buffer
for (ptr = inpbuf; *ptr != '\n'; ptr++)
    *ptr = ' ';
if (narg != 0) {
    arg[narg] = NULL;
}
}

void handle_SIGINT()
{
write(STDOUT_FILENO, buffer, strlen(buffer));
}

int main()
{
    int pid, exitstat, ret;
    struct sigaction handler;
    handler.sa_handler = handle_SIGINT;
    handler.sa_flags = 0;
    sigemptyset(&handler.sa_mask);
    sigaction(SIGINT, &handler, NULL);
    strcpy(buffer, "Caught Control C\n");

    while (1) {
        printf("%s ", prompt);
        fflush(stdout);
        getline();
        processline();
        if ((pid = fork()) < 0){
            fprintf(stderr, "myshell: error\n");
            return (-1);
        }

        if (pid == 0) {
            execvp(*arg, arg);
            fprintf(stderr, "%s\n", *arg);
            exit(127);
        }
        waitpid(pid, &exitstat, 0);
    }
    return 0;
}

Answer 1

Simplest solution would be to rename your getline() function, e.g. to my_getline()