dj(1), mm(1), npc(1), scrut(1), str(1): consistent argv[0] handling

src/dj.c

@@ -30,7 +30,7 @@
 
 extern int errno;
 
-char *program_name = "dj";
+static char *program_name = "dj";
 
 /* dj uses two structures that respectively correspond to the reading and
  * writing ends of its jockeyed "pipe". User-configurable members are noted
@@ -150,7 +150,7 @@ usage(char *s) {
 	fprintf(
 		stderr, "Usage: %s [-Hn] [-a byte] [-c count]\n"
 		"\t[-i file] [-b block_size] [-s offset]\n"
-		"\t[-o file] [-B block_size] [-S offset]\n", program_name
+		"\t[-o file] [-B block_size] [-S offset]\n", s
 	);
 
 	return EX_USAGE;
@@ -163,6 +163,7 @@ int main(int argc, char *argv[]) {
 	size_t i;     /* side of io being modified */
 	char noerror; /* 0=exits (default) 1=retries on partial reads or writes */
 	struct Io io[2 /* { in, out } */];
+	char *s = (argv[0] == NULL ? program_name : argv[0]);
 
 	/* Set defaults. */
 	align = -1;
@@ -233,7 +234,7 @@ int main(int argc, char *argv[]) {
 
 					/* FALLTHROUGH */
 				default:
-					return usage(program_name);
+					return usage(s);
 			}
 		}
 	}
@@ -241,7 +242,7 @@ int main(int argc, char *argv[]) {
 	assert(io->fd != STDIN_FILENO  || io->fl == read_flags);
 	assert(io->fd != STDOUT_FILENO || io->fl == write_flags);
 
-	if (argc > optind) { return usage(program_name); }
+	if (argc > optind) { return usage(s); }
 
 	for (i = 0; i < (sizeof io) / (sizeof *io); ++i) {
 		/* buffer allocation */