Look for full command names instead of substrings

like "un", "cat", and "lz" when determining if
xz is run as unxz, xzcat, lzma, unlzma, or lzcat.

This is to ensure that if xz is renamed (e.g. via
--program-transform-name), it doesn't so easily
work in wrong mode.

src/xz/args.c

@@ -465,19 +465,23 @@ args_parse(args_info *args, int argc, char **argv)
 		// NOTE: It's possible that name[0] is now '\0' if argv[0]
 		// is weird, but it doesn't matter here.
 
-		// If the command name contains "lz",
-		// it implies --format=lzma.
-		if (strstr(name, "lz") != NULL)
-			opt_format = FORMAT_LZMA;
-
-		// Operation mode
-		if (strstr(name, "cat") != NULL) {
-			// Imply --decompress --stdout
+		// Look for full command names instead of substrings like
+		// "un", "cat", and "lz" to reduce possibility of false
+		// positives when the programs have been renamed.
+		if (strstr(name, "xzcat") != NULL) {
 			opt_mode = MODE_DECOMPRESS;
 			opt_stdout = true;
-		} else if (strstr(name, "un") != NULL) {
-			// Imply --decompress
+		} else if (strstr(name, "unxz") != NULL) {
 			opt_mode = MODE_DECOMPRESS;
+		} else if (strstr(name, "lzcat") != NULL) {
+			opt_format = FORMAT_LZMA;
+			opt_mode = MODE_DECOMPRESS;
+			opt_stdout = true;
+		} else if (strstr(name, "unlzma") != NULL) {
+			opt_format = FORMAT_LZMA;
+			opt_mode = MODE_DECOMPRESS;
+		} else if (strstr(name, "lzma") != NULL) {
+			opt_format = FORMAT_LZMA;
 		}
 	}