separate out rot13(1)

rot13/Makefile

@@ -0,0 +1,26 @@
+all: rot13
+
+clean:
+	rm -rf ../dist/rot13 ../dist/rot13.tar ../dist/rot13.tar.gz rot13
+
+dist: ../dist/rot13.tar.gz
+
+sane: rot13.c ../include/sysexits.h
+	$(CC) -DDONT_USE_SYSTEM_SYSEXITS -o rot13 rot13.c
+rot13: rot13.c
+	$(CC) -o rot13 rot13.c
+
+../dist/rot13: rot13
+	mkdir -p ../dist/rot13.tmp/bin/
+	cp rot13 ../dist/rot13.tmp/bin/rot13
+	mv ../dist/rot13.tmp ../dist/rot13
+
+../dist/rot13.tar: ../dist/rot13
+	cd ../dist/rot13 && pax -w -x ustar . >../rot13.tar.tmp
+	mv ../dist/rot13.tar.tmp ../dist/rot13.tar
+
+../dist/rot13.tar.gz: ../dist/rot13.tar
+	gzip -c <../dist/rot13.tar >../dist/rot13.tar.gz.tmp
+	mv ../dist/rot13.tar.gz.tmp ../dist/rot13.tar.gz
+
+.PHONY: all clean sane

rot13/rot13.c

@@ -0,0 +1,68 @@
+#include <stddef.h> /* stdin, stdout */
+
+/* When rot13(1) is a part of ~trinity/src, which doesn't assume the system has
+ * <sysexits.h> and generates it out of a table. */
+#ifdef DONT_USE_SYSTEM_SYSEXITS
+#	include "../include/sysexits.h" /* EX_OK, EX_USAGE */
+#else
+#	include <sysexits.h> /* EX_OK, EX_USAGE */
+#endif
+
+#ifdef U_UNICODE_VERSION /* libicu Unicode support */
+#	define CHARACTER UChar32
+
+#	include <uchar.h> /* u_isupper(3) */
+#	define ISUPPER u_isupper
+
+#	include <ustdio.h> /* U_EOF */
+#	define ENDOFFILE U_EOF
+#else /* ifdef U_UNICODE_VERSION */
+#	define CHARACTER int
+
+#	include <ctype.h> /* isalpha(3), isupper(3) */
+#	define ISALPHA isalpha
+#	define ISUPPER isupper
+
+#	include <stdio.h> /* getc(3), putc(3) */
+#	define ENDOFFILE EOF
+#	define GETC getc
+#	define PUTC putc
+#endif /* ifdef U_UNICODE_VERSION */
+
+static char *program_name = "rot13";
+
+// /* Assumes this is a character in the provided glyph system.
+//  * Probably not Unicode-capable but doesn't assume Alphabet.
+//  * Returns `c` rotated around `a` by `r` characters. */
+// #include <string.h> /* strchr(3), strlen(3) */
+// static int
+// caesar(char c, int r, const char *a){
+// 	return a[(strchr(a, c) - a + r) % strlen(a)];
+// }
+
+/* Or... make some static arrays of the alphabet * 1.5, so c + '\0' + 13 is
+ * always a valid index and always reflects the correct rotation (13 places).
+ */
+static char alpha_upper[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLM";
+static char alpha_lower[] = "abcdefghijklmnopqrstuvwxyzabcdefghijklm";
+
+int main(int argc, char *argv[]){
+	char *a; /* easier than doing freaky math */
+	CHARACTER c;
+
+	if(argc > 1){
+		fprintf(stderr, "Usage: %s\n",
+			argv[0] == NULL ? program_name : argv[0]
+		);
+		return EX_USAGE;
+	}
+
+	while((c = getc(stdin)) != EOF)
+		if(isalpha(c)){
+			a = isupper(c) ? alpha_upper : alpha_lower;
+			putc(a[c - a[0] + 13], stdout);
+		}else
+			putc(c, stdout);
+
+	return EX_OK;
+}