Reinstate revision 1.11:

BDECFLAGS; ANSIfy; use EXEC instead of "exec " where appropriate; use
proper types (size_t, int); use proper variable names for certain things;
get rid of static 'cache' style stuff by moving and sanitizing the
original SHELL checking code to main(), this also makes it easier to
free() the string; rename file-scope system() to exec_shell(); use
snprintf() everywhere instead of sprintf(); actually remember to free()
other malloc()'d char pointers in main().

I left out the -s option in this revision along with getusershell()
checking because of objections made by Warner Losh <imp> and Garrett
Wollman <wollman>.  I agreed with their assertions that such code was
unnecessary in a program like this.

I dare people to make this coredump now.

Some suggestions:	nectar (snprintf() truncate checking)
Reviewed by:		markm, eivind, jedgar
Tortured by:		examples in apply(1), fuzz(1),
			and a lot of random ideas I came up with

usr.bin/apply/apply.c

@@ -55,16 +55,16 @@ static const char rcsid[] =
 #include <string.h>
 #include <unistd.h>
 
-void	usage __P((void));
-int	system __P((const char *));
+void			usage(void);
+static int		exec_shell(char *, char *, const char *);
+
+#define	EXEC	"exec "
 
 int
-main(argc, argv)
-	int argc;
-	char *argv[];
-{
-	int ch, clen, debug, i, l, magic, n, nargs, rval;
-	char *c, *cmd, *p, *q;
+main(int argc, char **argv) {
+	int ch, debug, i, magic, n, nargs, rval, offset;
+	size_t clen, l, cmdsize;
+	char *c, *cmd, *p, *q, *shell, *name, *tmpshell, *slashp;
 
 	debug = 0;
 	magic = '%';		/* Default magic char is `%'. */
@@ -108,14 +108,32 @@ main(argc, argv)
 				n = p[0] - '0';
 		}
 
+	/*
+	 * Figure out the shell and name arguments to pass to execl()
+	 * in exec_shell().  Always malloc() shell and just set name
+	 * to point at the last part of shell if there are any backslashes,
+	 * otherwise just set it to point at the space malloc()'d.  If
+	 * SHELL environment variable exists, replace contents of
+	 * shell with it.
+	 */
+	shell = name = NULL;
+	tmpshell = getenv("SHELL");
+	shell = (tmpshell != NULL) ? strdup(tmpshell) : strdup(_PATH_BSHELL);
+	if (shell == NULL)
+		err(1, "strdup() failed");
+	slashp = strrchr(shell, '/');
+	name = (slashp != NULL) ? slashp + 1 : shell;
+
 	/*
 	 * If there were any %digit references, then use those, otherwise
 	 * build a new command string with sufficient %digit references at
 	 * the end to consume (nargs) arguments each time round the loop.
-	 * Allocate enough space to hold the maximum command.
+	 * Allocate enough space to hold the maximum command.  Save the
+	 * size to pass to snprintf().
 	 */
-	if ((cmd = malloc(sizeof("exec ") - 1 +
-	    strlen(argv[0]) + 9 * (sizeof(" %1") - 1) + 1)) == NULL)
+	cmdsize = sizeof(EXEC) - 1 + strlen(argv[0]) + 9 *
+		(sizeof(" %1") - 1) + 1;
+	if ((cmd = malloc(cmdsize)) == NULL)
 		err(1, NULL);
 
 	if (n == 0) {
@@ -124,9 +142,16 @@ main(argc, argv)
 			nargs = 1;
 
 		p = cmd;
-		p += sprintf(cmd, "exec %s", argv[0]);
-		for (i = 1; i <= nargs; i++)
-			p += sprintf(p, " %c%d", magic, i);
+		offset = snprintf(cmd, cmdsize, EXEC "%s", argv[0]);
+		if ((size_t)offset >= cmdsize)
+			err(1, "snprintf() failed");
+		p += offset;
+		for (i = 1; i <= nargs; i++) {
+			offset = snprintf(p, cmdsize, " %c%d", magic, i);
+			if ((size_t)offset >= cmdsize)
+				err(1, "snprintf() failed");
+			p += offset;
+		}
 
 		/*
 		 * If nargs set to the special value 0, eat a single
@@ -135,7 +160,9 @@ main(argc, argv)
 		if (nargs == 0)
 			nargs = 1;
 	} else {
-		(void)sprintf(cmd, "exec %s", argv[0]);
+		offset = snprintf(cmd, cmdsize, EXEC "%s", argv[0]);
+		if ((size_t)offset >= cmdsize)
+			err(1, "snprintf() failed");
 		nargs = n;
 	}
 
@@ -164,9 +191,13 @@ main(argc, argv)
 
 		/* Expand command argv references. */
 		for (p = cmd, q = c; *p != '\0'; ++p)
-			if (p[0] == magic && isdigit(p[1]) && p[1] != '0')
-				q += sprintf(q, "%s", argv[(++p)[0] - '0']);
-			else
+			if (p[0] == magic && isdigit(p[1]) && p[1] != '0') {
+				offset = snprintf(q, l, "%s",
+				    argv[(++p)[0] - '0']);
+				if ((size_t)offset >= l)
+					err(1, "snprintf() failed");
+				q += offset;
+			} else
 				*q++ = *p;
 
 		/* Terminate the command string. */
@@ -176,38 +207,32 @@ main(argc, argv)
 		if (debug)
 			(void)printf("%s\n", c);
 		else
-			if (system(c))
+			if (exec_shell(shell, name, c))
 				rval = 1;
 	}
 
 	if (argc != 1)
 		errx(1, "expecting additional argument%s after \"%s\"",
-		    (nargs - argc) ? "s" : "", argv[argc - 1]);
+	    (nargs - argc) ? "s" : "", argv[argc - 1]);
+	
+	free(cmd);
+	free(c);
+	free(shell);
 	exit(rval);
 }
 
 /*
- * system --
- * 	Private version of system(3).  Use the user's SHELL environment
- *	variable as the shell to execute.
+ * exec_shell --
+ * 	Execute a shell command using passed use_shell and use_name
+ * 	arguments.
  */
-int
-system(command)
-	const char *command;
+static int
+exec_shell(char *use_shell, char *use_name, const char *command)
 {
-	static char *name, *shell;
 	pid_t pid;
 	int omask, pstat;
 	sig_t intsave, quitsave;
 
-	if (shell == NULL) {
-		if ((shell = getenv("SHELL")) == NULL)
-			shell = _PATH_BSHELL;
-		if ((name = strrchr(shell, '/')) == NULL)
-			name = shell;
-		else
-			++name;
-	}
 	if (!command)		/* just checking... */
 		return(1);
 
@@ -217,8 +242,8 @@ system(command)
 		err(1, "vfork");
 	case 0:				/* child */
 		(void)sigsetmask(omask);
-		execl(shell, name, "-c", command, NULL);
-		warn("%s", shell);
+		execl(use_shell, use_name, "-c", command, NULL);
+		warn("%s", use_shell);
 		_exit(1);
 	}
 	intsave = signal(SIGINT, SIG_IGN);