first usable version of kernel and commands

After an year of hard work, this is a first "usable" version of Jehanne.

sys/src/lib/regexp/regsub.c

@@ -0,0 +1,72 @@
+/*
+ * This file is part of the UCB release of Plan 9. It is subject to the license
+ * terms in the LICENSE file found in the top-level directory of this
+ * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
+ * part of the UCB release of Plan 9, including this file, may be copied,
+ * modified, propagated, or distributed except according to the terms contained
+ * in the LICENSE file.
+ */
+
+#include <u.h>
+#include <libc.h>
+#include "regexp.h"
+
+/* substitute into one string using the matches from the last regexec() */
+extern	void
+regsub(char *sp,	/* source string */
+	char *dp,	/* destination string */
+	int dlen,
+	Resub *mp,	/* subexpression elements */
+	int ms)		/* number of elements pointed to by mp */
+{
+	char *ssp, *ep;
+	int i;
+
+	ep = dp+dlen-1;
+	while(*sp != '\0'){
+		if(*sp == '\\'){
+			switch(*++sp){
+			case '0':
+			case '1':
+			case '2':
+			case '3':
+			case '4':
+			case '5':
+			case '6':
+			case '7':
+			case '8':
+			case '9':
+				i = *sp-'0';
+				if(mp!=0 && mp[i].sp != 0 && ms>i)
+					for(ssp = mp[i].sp;
+					     ssp < mp[i].ep;
+					     ssp++)
+						if(dp < ep)
+							*dp++ = *ssp;
+				break;
+			case '\\':
+				if(dp < ep)
+					*dp++ = '\\';
+				break;
+			case '\0':
+				sp--;
+				break;
+			default:
+				if(dp < ep)
+					*dp++ = *sp;
+				break;
+			}
+		}else if(*sp == '&'){
+			if(mp!=0 && mp[0].sp != 0 && ms>0)
+				for(ssp = mp[0].sp;
+				     ssp < mp[0].ep; ssp++)
+					if(dp < ep)
+						*dp++ = *ssp;
+		}else{
+			if(dp < ep)
+				*dp++ = *sp;
+		}
+		sp++;
+	}
+	*dp = '\0';
+}