pathsearch.c

#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
 
#define COUNTOF(arr) (sizeof(arr) / sizeof(arr[0]))
 
char* pathsearch(const char* program)
{
    char buffer[4096];
    char* path = strdup(getenv("PATH"));
    char* path_start = path;
    int path_length = strlen(path);
    char* colon = NULL;
    char* found_path = NULL;
 
    while (path - path_start < path_length)
    {
        colon = strchr(path, ':');
 
        if (colon != NULL)
            *colon = '\0';
 
        buffer[0] = '\0';
 
        if (strlen(path) != 0)
            snprintf(buffer, COUNTOF(buffer), "%s/%s", path, program);
 
        if (colon != NULL) {
            path = colon + 1;
        } else {
            break;
        }
 
        if (buffer[0] == '\0')
            continue;
 
        if(access(buffer, X_OK) == 0) {
            found_path = buffer;
            break;
        }
    }
 
    free(path_start);
 
    return found_path == NULL ? found_path : strdup(found_path);
}
 
int main()
{
    char* fullpath = pathsearch("ls");
    printf("%s\n", fullpath == 0 ? "<none>" : fullpath);
    free(fullpath);
    return 0;
}