Make sh(1) support \u in PS1. This removes one fork/exec on interactive

shell startup.

Reviewed by:	0mp (man page), jilles
MFC after:	2 weeks
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D18790

bin/sh/parser.c

@@ -40,6 +40,8 @@ static char sccsid[] = "@(#)parser.c	8.7 (Berkeley) 5/16/95";
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <sys/param.h>
+#include <pwd.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <stdio.h>
@@ -130,6 +132,7 @@ static void synexpect(int) __dead2;
 static void synerror(const char *) __dead2;
 static void setprompt(int);
 static int pgetc_linecont(void);
+static void getusername(char *, size_t);
 
 
 static void *
@@ -1969,6 +1972,53 @@ pgetc_linecont(void)
 	return (c);
 }
 
+
+static struct passwd *
+getpwlogin(void)
+{
+	const char *login;
+
+	login = getlogin();
+	if (login == NULL)
+		return (NULL);
+
+	return (getpwnam(login));
+}
+
+
+static void
+getusername(char *name, size_t namelen)
+{
+	static char cached_name[MAXLOGNAME];
+	struct passwd *pw;
+	uid_t euid;
+
+	if (cached_name[0] == '\0') {
+		euid = geteuid();
+
+		/*
+		 * Handle the case when there is more than one
+		 * login with the same UID, or when the login
+		 * returned by getlogin(2) does no longer match
+		 * the current UID.
+		 */
+		pw = getpwlogin();
+		if (pw == NULL || pw->pw_uid != euid)
+			pw = getpwuid(euid);
+
+		if (pw != NULL) {
+			strlcpy(cached_name, pw->pw_name,
+			    sizeof(cached_name));
+		} else {
+			snprintf(cached_name, sizeof(cached_name),
+			    "%u", euid);
+		}
+	}
+
+	strlcpy(name, cached_name, namelen);
+}
+
+
 /*
  * called by editline -- any expansions to the prompt
  *    should be added here.
@@ -2026,6 +2076,17 @@ getprompt(void *unused __unused)
 				--i;
 				break;
 
+				/*
+				 * User name.
+				 */
+			case 'u':
+				ps[i] = '\0';
+				getusername(&ps[i], PROMPTLEN - i);
+				/* Skip to end of username. */
+				while (ps[i + 1] != '\0')
+					i++;
+				break;
+
 				/*
 				 * Working directory.
 				 *

bin/sh/sh.1

@@ -32,7 +32,7 @@
 .\"	from: @(#)sh.1	8.6 (Berkeley) 5/4/95
 .\" $FreeBSD$
 .\"
-.Dd December 8, 2018
+.Dd January 24, 2019
 .Dt SH 1
 .Os
 .Sh NAME
@@ -1402,6 +1402,8 @@ which are replaced by the given information:
 This system's fully-qualified hostname (FQDN).
 .It Li \eh
 This system's hostname.
+.It Li \eu
+User name.
 .It Li \eW
 The final component of the current working directory.
 .It Li \ew

share/skel/dot.shrc

@@ -33,7 +33,7 @@ alias g='egrep -i'
 
 
 # set prompt: ``username@hostname:directory $ '' 
-PS1="`whoami`@\h:\w \\$ "
+PS1="\u@\h:\w \\$ "
 
 # search path for cd(1)
 # CDPATH=:$HOME