Index: parser.c
===================================================================
RCS file: /cvsroot/src/bin/sh/parser.c,v
retrieving revision 1.54
diff -u -u -r1.54 parser.c
--- parser.c	2002/11/24 22:35:42	1.54
+++ parser.c	2003/01/18 10:38:58
@@ -46,6 +46,7 @@
 #endif /* not lint */
 
 #include <stdlib.h>
+#include <unistd.h>
 
 #include "shell.h"
 #include "parser.h"
@@ -1608,21 +1609,89 @@
 		out2str(getprompt(NULL));
 }
 
+/* used by getprompt */
+#define STR_REALLOC(str,actual,add) \
+	if (actual < strlen(str) + add) { \
+		str = (char *) realloc(str, actual + add); \
+		actual += add; \
+	}
+
 /*
  * called by editline -- any expansions to the prompt
  *    should be added here.
  */
 const char *
 getprompt(void *unused)
-	{
+{
+	const char *unexp;			/* Unexpanded path */
+	static char *exp = NULL;		/* Expanded path */
+	static int alloclen = 0;		/* Allocated memory in exp */
+	unsigned long pos = 0;			/* Current position in exp */
+	int err;
+	char hostname[MAXHOSTNAMELEN + 1];
+	char *cwd;
+
+	/* Set unexp to the requested prompt if it requires expansion,
+	 * otherwise return its value directly. */
 	switch (whichprompt) {
 	case 0:
 		return "";
 	case 1:
-		return ps1val();
+		unexp = ps1val();
+		break;
 	case 2:
-		return ps2val();
+		unexp = ps2val();
+		break;
 	default:
 		return "<internal prompt error>";
 	}
+
+	if (alloclen == 0) {
+		alloclen = strlen(unexp) + 1;
+		exp = (char *) malloc(alloclen);
+	}
+	*exp = '\0';
+
+	while (*unexp != '\0') {
+		err = 0;
+
+		if (*unexp == '\\') {
+			unexp++;	/* Skip backslash */
+			switch (*unexp) {
+			case 'm':	/* Short hostname */
+				gethostname(hostname, MAXHOSTNAMELEN);
+				STR_REALLOC(exp, alloclen, strlen(hostname)+1);
+				strcat(exp, hostname);
+				pos += strlen(hostname);
+				break;
+			case 'w':	/* Current working directory */
+				cwd = getcwd(NULL, 0);
+				if (cwd == NULL) {
+					err = 1;
+					cwd = "<cwd disappeared>";
+				}
+				STR_REALLOC(exp, alloclen, strlen(cwd)+1);
+				strcat(exp, cwd);
+				pos += strlen(cwd);
+				if (!err)
+					free(cwd);
+				break;
+			case '#':	/* # for root, $ for user */
+				if (geteuid())
+					exp[pos++] = '$';
+				else
+					exp[pos++] = '#';
+				break;
+			default:
+				exp[pos++] = *unexp;
+				break;
+			}
+		} else
+			exp[pos++] = *unexp;
+
+		unexp++;
+		exp[pos] = '\0';
+	}
+
+	return exp;
 }
Index: sh.1
===================================================================
RCS file: /cvsroot/src/bin/sh/sh.1,v
retrieving revision 1.55
diff -u -u -r1.55 sh.1
--- sh.1	2002/12/28 05:08:27	1.55
+++ sh.1	2003/01/18 10:38:58
@@ -1031,6 +1031,30 @@
 patterns used for both Pathname Expansion and the
 .Ic case
 command.
+.Ss Prompt expansion
+Prompt variables,
+.Va PS1
+and
+.Va PS2 ,
+are subject to prompt expansion each time they are shown.
+The following sequences are recognized, and can appear any number of
+times inside prompt variables:
+.Bl -tag -width indent
+.It \em
+Machine's hostname, up to the first dot.
+.It \ew
+Full path of the current working directory.
+.It \e#
+A
+.Ql $
+sign if the shell is running as a regular user, or a
+.Ql #
+sign if running as root.
+.El
+.Pp
+Note that backslashes must be quoted with another backslash, like
+.Ql \e\e ,
+in order to avoid parsing of escape sequences.
 .Ss Shell Patterns
 A pattern consists of normal characters, which match themselves,
 and meta-characters.