why wouldn't ls work with execvp? - c

Question

I have an assignment requesting me to write a mini-shell - something that will get a command to execute, execute it, and wait for some more commands.
when I pass to this mini-shell the command ls . it prints the contest of the current directory. When I pass to it ls it prints nothing. Why?
here is my code:
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>
#include <stdlib.h>
#include <stdbool.h>
#define MAX_CMD_SIZE 40
char** parse(char*);//will parse the arguments for the execv/excevp commands.
int main(int argc, char** argv)
{
bool debug = false;
assert(argc <= 2);
if (argc == 2)
{
//check for string -debug
debug = true;
}
if (debug)
printf("INFO: Father started PID[%d]\n", getpid());
char *command = malloc(MAX_CMD_SIZE);
while(true)
{
printf("minishell> ");
fgets(command, MAX_CMD_SIZE, stdin);
if (strcmp(command, "exit\n") == 0)
return 0;
pid_t pid = fork();
assert(pid >= 0);
if (pid == 0) //child
{
if (debug)
printf("INFO: Child started PID[%d]\n", getpid());
char** buf = parse(command);
if (debug)
{
int i;
for (i = 0; buf[i]; i++)
printf("INFO: buf[%d] = %s\n",i,buf[i]);
}
execvp(buf[0],buf);
return 0;
}
else //father
{
int status;
wait(&status);
if (debug)
printf("INFO: Child with PID[%d]terminated, continue waiting commands\n", pid);
}
}
}
char** parse(char *string)
{
char** ret = malloc(sizeof(char*));
ret[0] = strtok(string, " ");
int i = 0;
for (; ret[i]; ret[i] = strtok(NULL, " \n"))
{
ret = realloc(ret, sizeof(char*) * ++i);
}
return ret;
}

Answer 1

Your parse() command includes a \n in the last argument :)
So with a single ls, you're actually executing ls\n, which is not in the PATH (of course)
The problem is that on the first strtok() call, you only pass " " as a delimiter. Use " \n" (like in the subsequent calls) and the problem goes away.
You could also fix it by chomping the \n:
int l = strlen (string);
if (l > 0 && string [l - 1] == '\n') string [l - 1] = '\0';
and only using " " as a delimiter.