Weird behavior of fork() and execvp() in C
- by ron
After some remarks from my previous post , I made the following modifications :
int main()
{
char errorStr[BUFF3];
while (1)
{
int i , errorFile;
char *line = malloc(BUFFER);
char *origLine = line;
fgets(line, 128, stdin); // get a line from stdin
// get complete diagnostics on the given string
lineData info = runDiagnostics(line);
char command[20];
sscanf(line, "%20s ", command);
line = strchr(line, ' '); // here I remove the command from the line , the command is stored in "commmand" above
printf("The Command is: %s\n", command);
int currentCount = 0; // number of elements in the line
int *argumentsCount = ¤tCount; // pointer to that
// get the elements separated
char** arguments = separateLineGetElements(line,argumentsCount);
printf("\nOutput after separating the given line from the user\n");
for (i = 0; i < *argumentsCount; i++) {
printf("Argument %i is: %s\n", i, arguments[i]);
}
// here we call a method that would execute the commands
pid_t pid ;
if (-1 == (pid = fork()))
{
sprintf(errorStr,"fork: %s\n",strerror(errno));
write(errorFile,errorStr,strlen(errorStr + 1));
perror("fork");
exit(1);
}
else if (pid == 0) // fork was successful
{
printf("\nIn son process\n");
// if (execvp(arguments[0],arguments) < 0) // for the moment I ignore this line
if (execvp(command,arguments) < 0) // execute the command
{
perror("execvp");
printf("ERROR: execvp failed\n");
exit(1);
}
}
else // parent
{
int status = 0;
pid = wait(&status);
printf("Process %d returned with status %d.", pid, status);
}
// print each element of the line
for (i = 0; i < *argumentsCount; i++) {
printf("Argument %i is: %s\n", i, arguments[i]);
}
// free all the elements from the memory
for (i = 0; i < *argumentsCount; i++) {
free(arguments[i]);
}
free(arguments);
free(origLine);
}
return 0;
}
When I enter in the Console :
ls out.txt
I get :
The Command is: ls
execvp: No such file or directory
In son process
ERROR: execvp failed
Process 4047 returned with status 256.Argument 0 is: >
Argument 1 is: out.txt
So I guess that the son process is active , but from some reason the execvp fails .
Why ?
Regards
REMARK :
The ls command is just an example . I need to make this works with any given command .
EDIT 1 :
User input : ls > qq.out
Program output :
The Command is: ls
Output after separating the given line from the user
Argument 0 is: >
Argument 1 is: qq.out
In son process
>: cannot access qq.out: No such file or directory
Process 4885 returned with status 512.Argument 0 is: >
Argument 1 is: qq.out
