expandpath.c

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>

#define EXPANDPATH_MAX 256
char *expandpath(const char *cmd)
{
        struct stat st;
        char *pathele, *clpt;   /* path element, colon pointer */
        static char apath[EXPANDPATH_MAX];

        pathele = getenv("PATH");
        assert(pathele);
        for (clpt = strchr(pathele, ':'); clpt; pathele = clpt + 1, clpt = strchr(pathele, ':')) {
                snprintf(apath, EXPANDPATH_MAX, "%.*s/%s", (int)(clpt - pathele), pathele, cmd);
                if (!stat(apath, &st))
                        return apath;
        }
        snprintf(apath, EXPANDPATH_MAX, "%s/%s", pathele, cmd);
        if (!stat(apath, &st))
            return apath;

        return NULL;
}

int main(int argc, char **argv)
{
        char *ptr;

        assert(argv[1]);
        ptr = expandpath(argv[1]);
        printf("%s\n", (ptr ? ptr : "Not found"));
        return 0;
}