Add and document support for handling comments and blank lines

in /etc/sysctl.conf.

Reviewed by:	imp, jkh

etc/rc.d/sysctl

@@ -4,10 +4,13 @@
 #
 # $FreeBSD$
 if [ -f /etc/sysctl.conf ]; then
-	3< /etc/sysctl.conf
-	while read 0<&3 var;
+	sed '
+		/^[  	]*#/d
+		/^[ 	]*$/d
+		s/#.*$//g
+	' /etc/sysctl.conf |
+	while read var
 	do
 		sysctl -w ${var}
 	done
-	3<&-
 fi

etc/rc.sysctl

@@ -4,10 +4,13 @@
 #
 # $FreeBSD$
 if [ -f /etc/sysctl.conf ]; then
-	3< /etc/sysctl.conf
-	while read 0<&3 var;
+	sed '
+		/^[  	]*#/d
+		/^[ 	]*$/d
+		s/#.*$//g
+	' /etc/sysctl.conf |
+	while read var
 	do
 		sysctl -w ${var}
 	done
-	3<&-
 fi

share/man/man5/sysctl.conf.5

@@ -42,6 +42,13 @@ command, i.e.
 .Bd -literal -offset indent
 sysctl_mib=value
 .Ed
+.Pp
+Comments are denoted by a
+.Dq #
+at the beginning of a line.  Comments can also exist at the end of a line,
+as seen in the
+.Sx EXAMPLES
+section, below.
 .Sh FILES
 .Bl -tag -width /etc/sysctl.conf -compact
 .It Pa /etc/sysctl.conf
@@ -52,7 +59,8 @@ To turn off logging of programs that exit due to fatal signals, as well as
 telling Linux programs that you are running FreeBSD 3.4-STABLE, you may use
 a configuration like
 .Bd -literal -offset indent
-kern.logsigexit=0
+# Configure logging and Linux execution.
+kern.logsigexit=0	# Do not log fatal signal exits (e.g. sig 11)
 compat.linux.osname=FreeBSD
 compat.linux.osrelease=3.4-STABLE
 .Ed