peek(1): fix erroring on stdin/stdout redirection

src/peek.c

@@ -62,6 +62,9 @@ usage(char *argv0) {
 }
 
 int main(int argc, char *argv[]){
+	bool is_term; /* Is stdin a terminal? */
+	bool must_be_term = 1; /* Must it be? */
+
 #ifdef __OpenBSD__
 	if (pledge("stdio tty unveil", "") != 0 || unveil(NULL, NULL) != 0) {
 		/* This isn't fatal; these return values could be cast to void just as
@@ -70,58 +73,63 @@ int main(int argc, char *argv[]){
 	}
 #endif
 
+	is_term = isatty(STDIN_FILENO);
+
 	if (argc > 0) { /* option parsing */
-		bool allow_nonterminals;
 		int c;
 
 		program_name = argv[0];
 
-		allow_nonterminals = 0;
 		while ((c = getopt(argc, argv, "i")) != -1) {
 			switch (c) {
-				case 'i':	allow_nonterminals = 1; break;
+				case 'i':	must_be_term = 0; break;
 				default:	return usage(argv[0]);
 			}
 		}
 
 		if (argc > optind) { return usage(argv[0]); }
-
-		if (!allow_nonterminals && isatty(STDIN_FILENO) != 1) {
-			(void)fprintf(
-			    stderr,
-			    "%s: Must be run in a terminal (specify -i to skip this"
-			    " check)\n",
-			    argv[0]
-			);
-			return EX_USAGE;
-		}
 	}
 
-	{ /* Install signal handler */
+	if (!is_term && must_be_term) {
-		/* There isn't a difference in functionality between the signal(2) and
+		(void)fprintf(
-		 * sigaction(2) methods. sigaction(2) is vastly preferred for
+		    stderr,
-		 * portability but some configurations can only use signal(2). */
+		    "%s: Must be run in a terminal (specify -i to skip this check)\n",
-		/* Errors aren't terminating because the worst that happens is some
+		    argv[0]
-		 * terminal phooeyness if things go awry. */
+		);
+		return EX_USAGE;
+	}
+
+	if (is_term) {
+		{ /* Install signal handler */
+			/* There isn't a difference in functionality between the signal(2)
+			 * and sigaction(2) methods. sigaction(2) is vastly preferred for
+			 * portability but some older systems only have signal(2). */
+			/* Errors aren't terminating because the worst that happens is some
+			 * terminal phooeyness if things go awry. */
 #if defined _POSIX_C_SOURCE
-		struct sigaction act = { 0 };
+			struct sigaction act = { 0 };
 
-		act.sa_handler = restore_echo;
+			act.sa_handler = restore_echo;
-		if (sigaction(SIGINT, &act, NULL) != 0) { perror(program_name); }
+			if (sigaction(SIGINT, &act, NULL) != 0) { perror(program_name); }
 #else
-		if (signal(SIGINT, restore_echo) == SIG_ERR) { perror(program_name); }
+			if (signal(SIGINT, restore_echo) == SIG_ERR) {
+				perror(program_name);
+			}
 #endif
-	}
+		}
 
-	/* Banish terminal echo; this terminates when it fails, because it's the
+		{ /* Banish terminal echo */
-	 * whole point of the program. */
+			/* This terminates when it fails because it's the whole point of
-	{
+			 * the program. */
-		struct termios t;
+			struct termios t;
 
-		if (tcgetattr(STDIN_FILENO, &t) != 0) { return ioerr(program_name); }
+			if (tcgetattr(STDIN_FILENO, &t) != 0) {
-		t.c_lflag ^= ECHO;
+				return ioerr(program_name);
-		if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &t) != 0) {
+			}
-			return ioerr(program_name);
+			t.c_lflag ^= ECHO;
+			if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &t) != 0) {
+				return ioerr(program_name);
+			}
 		}
 	}
 
@@ -133,7 +141,7 @@ int main(int argc, char *argv[]){
 		}
 	}
 
-	restore_echo(0);
+	if (is_term) { restore_echo(0); }
 
 	return EX_OK;
 }