symbolic chmod, thanks pancake

LICENSE

@@ -5,6 +5,7 @@ MIT/X Consortium License
 © 2011 stateless <stateless@archlinux.us>
 © 2011 Rob Pilling <robpilling@gmail.com>
 © 2011 Hiltjo Posthuma <hiltjo@codemadness.org>
+© 2011 pancake <pancake@youterm.com>
 
 Permission is hereby granted, free of charge, to any person obtaining a
 copy of this software and associated documentation files (the "Software"),

chmod.1

@@ -4,18 +4,65 @@ chmod \- change file mode
 .SH SYNOPSIS
 .B chmod
 .RB [ \-Rr ]
-.RI mode
+.I octal
+.RI [ file ...]
+.P
+.B chmod
+.RB [ \-Rr ]
+.RB [ ugoa ][ +-= ][ rwxs ]
 .RI [ file ...]
 .SH DESCRIPTION
 .B chmod
-changes the file mode for the given files.  The
+changes the file mode for the given files.
-.I mode
-is a four digit octal number derived from its comprising bits.
 .P
-The first digit defines the setuid (4) and setgid (2) attributes.  The second
+If the mode is an
-digit defines the owner's permissions: read (4), write (2), and execute (1); the
+.I octal
-third defines permissions for others in the file's group; and the fourth for all
+number, the modes are set according to that number's comprising bits. The first
-other users. Leading zeroes may be omitted.
+digit defines the setuid (4) and setgid (2) attributes.  The second digit
+defines the owner's permissions: read (4), write (2), and execute (1); the third
+defines permissions for others in the file's group; and the fourth for all other
+users. Leading zeroes may be omitted.
+.P
+Alternatively the mode may be symbolic. The symbol meanings are:
+.TP
+.B u
+modifies owner permissions.
+.PD 0
+.TP
+.B g
+modifies group permissions.
+.TP
+.B o
+modifies other user permissions.
+.TP
+.B a
+modifies all user permissions.
+.PD
+.TP
+.B +
+adds the given permissions to the mode.
+.PD 0
+.TP
+.B -
+removes the given permissions from the mode.
+.TP
+.B =
+sets the mode to the given permissions.
+.PD
+.TP
+.B r
+read permissions.
+.PD 0
+.TP
+.B w
+write permissions.
+.TP
+.B x
+execute permissions.
+.TP
+.B s
+setuid and setgid attributes.
+.PD
 .SH OPTIONS
 .TP
 .B \-R, \-r

chmod.c

@@ -7,15 +7,16 @@
 #include "util.h"
 
 static void chmodr(const char *);
+static void parsemode(const char *);
 
 static bool rflag = false;
+static char oper = '=';
 static mode_t mode = 0;
 
 int
 main(int argc, char *argv[])
 {
 	char c;
-	int octal;
 
 	while((c = getopt(argc, argv, "Rr")) != -1)
 		switch(c) {
@@ -28,9 +29,45 @@ main(int argc, char *argv[])
 		}
 	if(optind == argc)
 		eprintf("usage: %s [-Rr] mode [file...]\n", argv[0]);
-	octal = estrtol(argv[optind++], 8);
 
-	/* posix doesn't specify modal bits */
+	parsemode(argv[optind++]);
+	for(; optind < argc; optind++)
+		chmodr(argv[optind]);
+	return EXIT_SUCCESS;
+}
+
+void
+chmodr(const char *path)
+{
+	struct stat st;
+
+	if(stat(path, &st) == -1)
+		eprintf("stat %s:", path);
+
+	switch(oper) {
+	case '+':
+		st.st_mode |= mode;
+		break;
+	case '-':
+		st.st_mode &= ~mode;
+		break;
+	}
+	if(chmod(path, st.st_mode) == -1)
+		eprintf("chmod %s:", path);
+	if(rflag)
+		recurse(path, chmodr);
+}
+
+void
+parsemode(const char *str)
+{
+	char *end;
+	const char *p;
+	int octal;
+	mode_t mask = 0;
+
+	octal = strtol(str, &end, 8);
+	if(*end == '\0') {
 		if(octal & 04000) mode |= S_ISUID;
 		if(octal & 02000) mode |= S_ISGID;
 		if(octal & 00400) mode |= S_IRUSR;
@@ -42,17 +79,46 @@ main(int argc, char *argv[])
 		if(octal & 00004) mode |= S_IROTH;
 		if(octal & 00002) mode |= S_IWOTH;
 		if(octal & 00001) mode |= S_IXOTH;
-
+		return;
-	for(; optind < argc; optind++)
-		chmodr(argv[optind]);
-	return EXIT_SUCCESS;
 	}
-
+	for(p = str; *p; p++)
-void
+		switch(*p) {
-chmodr(const char *path)
+		/* masks */
-{
+		case 'u':
-	if(chmod(path, mode) == -1)
+			mask |= S_IRWXU;
-		eprintf("chmod %s:", path);
+			break;
-	if(rflag)
+		case 'g':
-		recurse(path, chmodr);
+			mask |= S_IRWXG;
+			break;
+		case 'o':
+			mask |= S_IRWXO;
+			break;
+		case 'a':
+			mask |= S_IRWXU|S_IRWXG|S_IRWXO;
+			break;
+		/* opers */
+		case '+':
+		case '-':
+		case '=':
+			oper = *p;
+			break;
+		/* modes */
+		case 'r':
+			mode |= S_IRUSR|S_IRGRP|S_IROTH;
+			break;
+		case 'w':
+			mode |= S_IWUSR|S_IWGRP|S_IWOTH;
+			break;
+		case 'x':
+			mode |= S_IXUSR|S_IXGRP|S_IXOTH;
+			break;
+		case 's':
+			mode |= S_ISUID|S_ISGID;
+			break;
+		/* error */
+		default:
+			eprintf("%s: invalid mode\n", str);
+		}
+	if(mask)
+		mode &= mask;
 }