`execvp()` seems to not be completing the path search - c

Question

TL;DR -- what sorts of things might cause an execvp call to not fully function/ search the path properly?
I'm on the tail end of building a rudimentary shell with some quality of life features that I've added over time e.g. history, alias's, and completions. I built those features on top of a functional shell that had a working $PATH search for execution e.g. typing in "ls -la" produced the desired behavior. As you might imagine, I accomplished this just using execvp. (This is written in C if it's not already clear)
I have not changed any of my tokenizing logic and have ensured that the file name is correct; in particular, execvp was producing the desired behavior before I had added these features to my REPL. echo "hello" still produces a tokenized char **xyz and the first token is indeed echo, null-terminated, and so on. That is, my call still looks like, with variables filled-in, ... execvp("echo", argv); after which I call perror, which should only trigger when something has gone awry. Each time I just run the above command, though, since I've added in these features, it returns a failure with the no such file or directory --- before I added these features in though, the behavior was as desired. I'll note, though, that running /bin/echo "hello" runs as expected. Examples are WLOG.
I'm not sure where I should even start looking for errors, and my Google-fu has been mostly fruitless: any suggestions?
I'm initially going to omit code because it totals to several hundred lines and a MWE would not be particularly minimal in addition to my desires to keep this general rather than very particular to my code, though I'm not sure what's causing this. My repository is public and up-to-date, and I'm happy to post any code here.
EDIT:
I knew I wasn't explicitly editing the PATH variable, etc., but this block of code was the problem:
// Grab $PATH from env
char *pathvar = getenv("PATH");
if (pathvar) {
char *path;
int i;
// tokenize on colon to get paths
// then use that immediately to
// scandir, and add everything in
// there to the completions system
path = strtok(pathvar, ":");
while (path) {
struct dirent **fListTemp;
int num_files = scandir(path, &fListTemp, NULL, alphasort);
// only adding the names that are completely composed of
// lower case letters; completions are done using a naive
// Trie Node structure that only supports lowercase letters
// for now... e.g. g++ does not work, and the '+' leads to
// a seg-fault. Same holds for . and ..
for (i = 0; i < num_files; i++) {
char *curr = fListTemp[i]->d_name;
if (strcmp(curr, ".")==0 || strcmp(curr, "..")==0){
continue;
} else if (notalpha(curr)) {
continue;
} else {
str_tolower(curr);
tn_insert(completions, curr);
}
}
for (i = 0; i < num_files; i++) {
free(fListTemp[i]);
}
free (fListTemp);
path = strtok(NULL, ":");
}
} else {
fprintf(stderr, "{wsh # init} -- $PATH variable could not be found?");
}

Answer 1

Note that
The getenv() function returns a pointer to the value in the
environment, or NULL if there is no match.
so my original code was indeed tampering with the PATH variable. The solution I came up with quickly was just to create a copy of that string and use that to parse through the PATH instead:
// Grab $PATH from env
char *pathvar = getenv("PATH");
char *pathvar_cpy = strcpy(pathvar_cpy, pathvar);
if (pathvar_cpy) {
char *path;
int i;
path = strtok(pathvar_cpy, ":");
while (path) {
// Scan directory
struct dirent **fListTemp;
int num_files = scandir(path, &fListTemp, NULL, alphasort);
for (i = 0; i < num_files; i++) {
char *curr = fListTemp[i]->d_name;
if (strcmp(curr, ".")==0 || strcmp(curr, "..")==0){
continue;
} else if (notalpha(curr)) {
continue;
} else {
str_tolower(curr);
tn_insert(completions, curr);
}
}
for (i = 0; i < num_files; i++) {
free(fListTemp[i]);
}
free (fListTemp);
path = strtok(NULL, ":");
}
} else {
fprintf(stderr, "{wsh # init} -- $PATH variable could not be found?");
}