sh: Add kill builtin.

This allows specifying a %job (which is equivalent to the corresponding
process group).

Additionally, it improves reliability of kill from sh in high-load
situations and ensures "kill" finds the correct utility regardless of PATH,
as required by POSIX (unless the undocumented %builtin mechanism is used).

Side effect: fatal errors (any error other than kill(2) failure) now return
exit status 2 instead of 1. (This is consistent with other sh builtins, but
not in NetBSD.)

Code size increases about 1K on i386.

Obtained from:	NetBSD

2 files changed, 33 insertions, 11 deletions

diff --git a/bin/kill/kill.1 b/bin/kill/kill.1
index c666ef5..6e77c59 100644
--- a/bin/kill/kill.1
+++ b/bin/kill/kill.1
@@ -134,6 +134,7 @@ Terminate the process group with PGID 117:
 .Xr csh 1 ,
 .Xr killall 1 ,
 .Xr ps 1 ,
+.Xr sh 1 ,
 .Xr kill 2 ,
 .Xr sigaction 2
 .Sh STANDARDS
diff --git a/bin/kill/kill.c b/bin/kill/kill.c
index f4ab2df..edfc928 100644
--- a/bin/kill/kill.c
+++ b/bin/kill/kill.c
@@ -49,6 +49,12 @@ __FBSDID("$FreeBSD$");
 #include <stdlib.h>
 #include <string.h>
 
+#ifdef SHELL
+#define main killcmd
+#include "bltin/bltin.h"
+#include "error.h"
+#endif
+
 static void nosig(const char *);
 static void printsignals(FILE *);
 static int signame_to_signum(const char *);
@@ -75,16 +81,16 @@ main(int argc, char *argv[])
 				usage();
 			numsig = strtol(*argv, &ep, 10);
 			if (!**argv || *ep)
-				errx(1, "illegal signal number: %s", *argv);
+				errx(2, "illegal signal number: %s", *argv);
 			if (numsig >= 128)
 				numsig -= 128;
 			if (numsig <= 0 || numsig >= sys_nsig)
 				nosig(*argv);
 			printf("%s\n", sys_signame[numsig]);
-			exit(0);
+			return (0);
 		}
 		printsignals(stdout);
-		exit(0);
+		return (0);
 	}
 
 	if (!strcmp(*argv, "-s")) {
@@ -107,7 +113,7 @@ main(int argc, char *argv[])
 		} else if (isdigit(**argv)) {
 			numsig = strtol(*argv, &ep, 10);
 			if (!**argv || *ep)
-				errx(1, "illegal signal number: %s", *argv);
+				errx(2, "illegal signal number: %s", *argv);
 			if (numsig < 0)
 				nosig(*argv);
 		} else
@@ -122,16 +128,23 @@ main(int argc, char *argv[])
 		usage();
 
 	for (errors = 0; argc; argc--, argv++) {
-		pid = strtol(*argv, &ep, 10);
-		if (!**argv || *ep)
-			errx(1, "illegal process id: %s", *argv);
-		else if (kill(pid, numsig) == -1) {
+#ifdef SHELL
+		if (**argv == '%')
+			pid = getjobpgrp(*argv);
+		else
+#endif
+		{
+			pid = strtol(*argv, &ep, 10);
+			if (!**argv || *ep)
+				errx(2, "illegal process id: %s", *argv);
+		}
+		if (kill(pid, numsig) == -1) {
 			warn("%s", *argv);
 			errors = 1;
 		}
 	}
 
-	exit(errors);
+	return (errors);
 }
 
 static int
@@ -154,7 +167,11 @@ nosig(const char *name)
 
 	warnx("unknown signal %s; valid signals:", name);
 	printsignals(stderr);
-	exit(1);
+#ifdef SHELL
+	error(NULL);
+#else
+	exit(2);
+#endif
 }
 
 static void
@@ -180,5 +197,9 @@ usage(void)
 		"       kill -l [exit_status]",
 		"       kill -signal_name pid ...",
 		"       kill -signal_number pid ...");
-	exit(1);
+#ifdef SHELL
+	error(NULL);
+#else
+	exit(2);
+#endif
 }