Audit readlink(1)

1) Properly document e, f and m-flags in the manpage.
2) Clear up the code for the m-flag-handling. Add idiomatic
   '/'-path-traversal as already seen in mkdir(1).
3) Unwrap the SWAP_BUF()-macro.
4) BUGFIX: Actually handle the f-flag properly. Only resolve
   the dirname and append the basename later.
5) Use fputs() instead of printf("%s", ...).

README

@@ -55,7 +55,7 @@ The following tools are implemented ('*' == finished, '#' == UTF-8 support,
 =*| printenv        non-posix                    none
 #*| printf          yes                          none
 =*| pwd             yes                          none
-=   readlink        non-posix                    none
+=*| readlink        non-posix                    none
 =*| renice          yes                          none
 =*| rm              yes                          none (-i)
 =*| rmdir           yes                          none

readlink.1

@@ -1,4 +1,4 @@
-.Dd January 31, 2015
+.Dd March 20, 2015
 .Dt READLINK 1
 .Os sbase
 .Sh NAME
@@ -6,30 +6,27 @@
 .Nd print symbolic link target or canonical file name
 .Sh SYNOPSIS
 .Nm
-.Op Fl fn
+.Op Fl e | Fl f | Fl m
-.Ar name
+.Op Fl n
+.Ar path
 .Sh DESCRIPTION
-If
-.Ar name
-is a symbolic link,
 .Nm
-writes its target to stdout.
+writes the target of
-If
+.Ar path ,
-.Fl f
+if it is a symbolic link, to stdout.
-is not set and
+If not,
-.Ar name
-is not a symbolic link,
 .Nm
-exits with a nonzero exit code without printing anything.
+exits with a non-zero return value.
 .Sh OPTIONS
 .Bl -tag -width Ds
-.It Fl f
+.It Fl e | Fl f | Fl m
 Canonicalize
 .Ar name ,
-which does not need to be a symlink,
+which needn't be a symlink,
-by recursively following every symlink in its components.
+by recursively following every symlink in its path components.
+All | All but the last | No path components must exist.
 .It Fl n
-Do not output the trailing newline.
+Do not print the terminating newline.
 .El
 .Sh SEE ALSO
 .Xr readlink 2 ,

readlink.c

@@ -1,6 +1,7 @@
 /* See LICENSE file for copyright and license details. */
 #include <sys/stat.h>
 
+#include <libgen.h>
 #include <unistd.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -11,18 +12,17 @@
 static void
 usage(void)
 {
-	eprintf("usage: %s [-efmn] name\n", argv0);
+	eprintf("usage: %s [-e | -f | -m] [-n] path\n", argv0);
 }
 
 int
 main(int argc, char *argv[])
 {
-	char buf1[PATH_MAX], buf2[PATH_MAX], arg[PATH_MAX];
-	int nflag = 0;
-	int mefflag = 0;
-	ssize_t n;
 	struct stat st;
-	char *p = arg, *lp = NULL, *b = buf1;
+	ssize_t n;
+	int nflag = 0, mefflag = 0;
+	char buf1[PATH_MAX], buf2[PATH_MAX], arg[PATH_MAX],
+	     *p, *slash, *prefix, *lp, *b = buf1;
 
 	ARGBEGIN {
 	case 'm':
@@ -40,57 +40,54 @@ main(int argc, char *argv[])
 	if (argc != 1)
 		usage();
 
-	if (strlen(argv[0]) > PATH_MAX - 1)
+	if (strlen(argv[0]) >= PATH_MAX)
 		eprintf("path too long\n");
 
-#define SWAP_BUF() (b = (b == buf1 ? buf2 : buf1));
 	switch (mefflag) {
 	case 'm':
-		if (argv[0][0] == '/') { /* case when path is on '/' */
+		slash = strchr(argv[0], '/');
-			arg[0] = '/';
+		prefix = (slash == argv[0]) ? "/" : (!slash) ? "./" : "";
-			arg[1] = '\0';
+
-			p++;
+		estrlcpy(arg, prefix, sizeof(arg));
-		} else if (!strchr(argv[0], '/')) { /* relative path */
-			arg[0] = '.';
-			arg[1] = '/';
-			arg[2] = '\0';
-		} else
-			arg[0] = '\0';
 		estrlcat(arg, argv[0], sizeof(arg));
-		while ((p = strchr(p, '/'))) {
+
+		for (lp = "", p = arg + (argv[0][0] == '/'); *p; p++) {
+			if (*p != '/')
+				continue;
 			*p = '\0';
 			if (!realpath(arg, b)) {
 				*p = '/';
 				goto mdone;
 			}
-			SWAP_BUF();
+			b = (b == buf1) ? buf2 : buf1;
 			lp = p;
-			*p++ = '/';
+			*p = '/';
 		}
 		if (!realpath(arg, b)) {
 mdone:
-			SWAP_BUF();
+			b = (b == buf1) ? buf2 : buf1;
-			if (lp) {
+			estrlcat(b, lp, sizeof(arg));
-				/* drop the extra '/' on root */
-				lp += (argv[0][0] == '/' &&
-				       lp - arg == 1);
-				estrlcat(b, lp, sizeof(arg));
-			}
 		}
 		break;
 	case 'e':
 		if (stat(argv[0], &st) < 0)
 			eprintf("stat %s:", argv[0]);
-	case 'f': /* fallthrough */
 		if (!realpath(argv[0], b))
 			eprintf("realpath %s:", argv[0]);
 		break;
+	case 'f':
+		p = dirname(estrdup(argv[0]));
+		if (!realpath(p, b))
+			eprintf("realpath %s:", p);
+		estrlcat(b, "/", sizeof(arg));
+		estrlcat(b, basename(estrdup(argv[0])), sizeof(arg));
+		break;
 	default:
 		if ((n = readlink(argv[0], b, PATH_MAX - 1)) < 0)
 			eprintf("readlink %s:", argv[0]);
 		b[n] = '\0';
 	}
-	printf("%s", b);
+	fputs(b, stdout);
 	if (!nflag)
 		putchar('\n');