Add logname util

src/logname.c

@@ -0,0 +1,26 @@
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+
+int usage(char *argv0) {
+  printf("Usage: %s\n", argv0);
+  return 1;
+}
+
+int main(int argc, char *argv[]){
+  int opt;
+  while ((opt = getopt(argc, argv, ":")) != -1) {
+    switch (opt) {
+      case '?':
+        fprintf(stderr, "%s: invalid option -- '%c'\n", argv[0], optopt);
+        return usage(argv[0]);
+    }
+  }
+
+  if (getlogin() != NULL) {
+    printf("%s\n", getlogin());
+  } else {
+    perror(argv[0]);
+  }
+  return errno;
+}