Using execvp in C to copy files under linux - c

Question

Ladies and gentlemen. I have a problem when using execvp inside a C program to copy files, it just doesn't want to work. The tar and mv commands do not work as well, and i presume that anything that has to do with creating files has some kind of problem as well. The weird thing is that commands like ls (with its options) and echo work as well when called with execvp.
Here is the code in question:
int main () {
char *curr_working_dir, *input, *inputCpy, *command, **args;
struct timeval start, end, duration;
system("clear");
while(1) {
curr_working_dir = getcwd(NULL, 0);
printf("%s $ ", curr_working_dir);
free(curr_working_dir);
fgets(input, 200, stdin);
input[strlen(input) - 1] = '\0';
inputCpy = cpyInput(input);
command = strtok(input, " ");
if(!(strcmp(command, "exit"))) {
break;
}
else if(!(strcmp(command, "cd"))) {
command = strtok(NULL, " ");
struct stat s;
if(!stat(command, &s) && S_ISDIR(s.st_mode)) {
chdir(command);
}
else {
chdir(getenv("HOME"));
}
free(inputCpy);
command = NULL;
}
else {
int pid = fork();
if(pid < 0) {
printf("Error al crear el proceso hijo\n");
}
else if(pid == 0) {
args = constructArgs(inputCpy);
execvp(command, args);
printf("execvp fallo: %s\n", strerror(errno));
}
else {
gettimeofday(&start, NULL);
wait((int*)NULL);
gettimeofday(&end, NULL);
timersub(&end, &start, &duration);
printf("Duracion del comando: %ld.%06ld\n", (long int)duration.tv_sec, (long int)duration.tv_usec);
free(inputCpy);
command = NULL;
}
}
}
return 0;
}
Here are some helper functions that i use in my program:
char **constructArgs(char *input) {
int i = 0;
char *argActual, **args;
argActual = strtok(input, " ");
args = malloc(sizeof(char *));
while(argActual != NULL) {
args[i] = malloc((strlen(argActual) + 1) * sizeof(char));
strcpy(args[i], argActual);
i += 1;
args = realloc(args, (i + 1) * sizeof(char *));
argActual = strtok(NULL, " ");
}
args[i] = NULL;
return args;
}
char *cpyInput(char *input) {
char *cpy;
cpy = malloc((strlen(input) + 1) * sizeof(char));
strcpy(cpy, input);
return cpy;
}
I use constructArgs to build an array of args to a particular program that i will call through execvp by parsing an input string containing the commands with its arguments. I can change directories, call echo, list the contents of directories, but when i try to run cp, or mv, or tar it doesn't do anything.
I have checked that i am sending the correct info to execvp; have a look at this for example:
let's say i have a file in /home/john/r1.sav and i want to copy this to another folder located in /home/john/anotherfolder. I debugged my program and this is what i am getting as the content for both the command and args arguments right before the call to execvp:
command = cp
args[0] = cp
args[1] = /home/john/r1.sav
args[2] = /home/john/anotherfolder
These are the expected inputs for execvp if you want to use cp through it. But it refuses to do anything. execvp receives as its first argument the name of the program to be executed, and an array of the arguments that the program is going to need, with the first argument in the array of arguments having the name of the program as well, which is what i'm doing. Everything works just fine with ls, or echo, but not with cp, or mv or tar.
Thank you in advance for any help you can shed on this peculiar problem.

Answer 1

I came across this post because I had the same issue. I don't know what the issue is, but once I declared an int for the return value it worked!
char *cmd = "cp";
char *argv[3];
argv[0] = "cp";
argv[1] = "source.c";
argv[2] = "destination.c;
int value = execvp(cmd, argv);
//Unreachable