From 4cc57221daee92b488db80dd8fb728a05d8042ea Mon Sep 17 00:00:00 2001
From: Devin Teske <dteske@FreeBSD.org>
Date: Thu, 7 Nov 2013 23:00:11 +0000
Subject: [PATCH] Add a `-c' option for `check only' to determine if a value is
 set (get command) or if the current value is the same as what is desired (set
 command). In those cases, the return status is success. Otherwise, if the
 variable is unset (get command) or set to a different value that what is
 desired (set command), returns with error status. This is useful for puppet
 integration as well as everyday scripting.

---
 usr.sbin/sysrc/sysrc   | 47 ++++++++++++++++++++++++++++++++++++------
 usr.sbin/sysrc/sysrc.8 | 10 +++++++--
 2 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/usr.sbin/sysrc/sysrc b/usr.sbin/sysrc/sysrc
index 01ea31f8115a..70676e2e8683 100644
--- a/usr.sbin/sysrc/sysrc
+++ b/usr.sbin/sysrc/sysrc
@@ -45,6 +45,7 @@ SYSRC_VERSION="6.0 Nov-07,2013"
 #
 # Options
 #
+CHECK_ONLY=
 DELETE=
 DESCRIBE=
 IGNORE_UNKNOWNS=
@@ -100,6 +101,8 @@ help()
 	      "Dump a list of all non-default configuration variables."
 	f_err "$optfmt" "-A" \
 	      "Dump a list of all configuration variables (incl. defaults)."
+	f_err "$optfmt" "-c" \
+	      "Check. Return success if no changes needed, else error."
 	f_err "$optfmt" "-d" \
 	      "Print a description of the given variable."
 	f_err "$optfmt" "-D" \
@@ -222,10 +225,11 @@ jail_depend()
 #
 # Process command-line flags
 #
-while getopts aAdDef:Fhij:nNqR:vxX flag; do
+while getopts aAcdDef:Fhij:nNqR:vxX flag; do
 	case "$flag" in
 	a) SHOW_ALL=${SHOW_ALL:-1};;
 	A) SHOW_ALL=2;;
+	c) CHECK_ONLY=1;;
 	d) DESCRIBE=1;;
 	D) RC_CONFS=;;
 	e) SHOW_EQUALS=1;;
@@ -286,6 +290,12 @@ if [ "$DELETE" -a "$SHOW_ALL" ]; then
 	[ "$DELETE" = "2" ] || die "$errmsg"
 fi
 
+#
+# Pre-flight for `-c' command-line option
+#
+[ "$CHECK_ONLY" -a "$SHOW_ALL" ] &&
+	die "$pgm: \`-c' option incompatible with \`-a'/\`-A' options"
+
 #
 # Process `-e', `-n', and `-N' command-line options
 #
@@ -312,6 +322,7 @@ if [ "$JAIL" -o "$ROOTDIR" ]; then
 		$( [ "$DELETE" = "2" ] && echo \ -X )
 		$( [ "$SHOW_ALL" = "1" ] && echo \ -a )
 		$( [ "$SHOW_ALL" = "2" ] && echo \ -A )
+		${CHECK_ONLY:+-c}
 		${DESCRIBE:+-d}
 		${SHOW_EQUALS:+-e}
 		${IGNORE_UNKNOWNS:+-i}
@@ -422,7 +433,7 @@ if [ "$SHOW_ALL" ]; then
 		EXCEPT="IFS|EXCEPT|PATH|RC_DEFAULTS|OPTIND|DESCRIBE|SEP"
 		EXCEPT="$EXCEPT|DELETE|SHOW_ALL|SHOW_EQUALS|SHOW_NAME"
 		EXCEPT="$EXCEPT|SHOW_VALUE|SHOW_FILE|SYSRC_VERBOSE|RC_CONFS"
-		EXCEPT="$EXCEPT|pgm|SUCCESS|FAILURE"
+		EXCEPT="$EXCEPT|pgm|SUCCESS|FAILURE|CHECK_ONLY"
 		EXCEPT="$EXCEPT|f_sysrc_desc_awk|f_sysrc_delete_awk"
 
 		#
@@ -515,6 +526,7 @@ fi
 #
 # Process command-line arguments
 #
+costatus=$SUCCESS
 while [ $# -gt 0 ]; do
 	NAME="${1%%=*}"
 
@@ -528,7 +540,7 @@ while [ $# -gt 0 ]; do
 		# first describe, then attempt to set
 		#
 
-		if [ "$SYSRC_VERBOSE" ]; then
+		if [ "$SYSRC_VERBOSE" -a ! "$CHECK_ONLY" ]; then
 			file=$( f_sysrc_find "$NAME" )
 			[ "$file" = "$RC_DEFAULTS" -o ! "$file" ] && \
 				file=$( f_sysrc_get 'rc_conf_files%%[$IFS]*' )
@@ -545,6 +557,20 @@ while [ $# -gt 0 ]; do
 			continue
 		fi
 
+		#
+		# If `-c' is passed, simply compare and move on
+		#
+		if [ "$CHECK_ONLY" ]; then
+			if ! IGNORED=$( f_sysrc_get "$NAME?" ); then
+				costatus=$FAILURE
+			else
+				value=$( f_sysrc_get "$NAME" )
+				[ "$value" = "${1#*=}" ] || costatus=$FAILURE
+			fi
+			shift 1
+			continue
+		fi
+
 		#
 		# If `-N' is passed, simplify the output
 		#
@@ -572,9 +598,16 @@ while [ $# -gt 0 ]; do
 		fi
 		;;
 	*)
-		if ! IGNORED="$( f_sysrc_get "$NAME?" )"; then
-			[ "$IGNORE_UNKNOWNS" ] \
-				|| echo "$pgm: unknown variable '$NAME'"
+		if ! IGNORED=$( f_sysrc_get "$NAME?" ); then
+			[ "$IGNORE_UNKNOWNS" ] ||
+				echo "$pgm: unknown variable '$NAME'"
+			shift 1
+			costatus=$FAILURE
+			continue
+		fi
+
+		# The above check told us what we needed for `-c'
+		if [ "$CHECK_ONLY" ]; then
 			shift 1
 			continue
 		fi
@@ -623,3 +656,5 @@ while [ $# -gt 0 ]; do
 	esac
 	shift 1
 done
+
+[ ! "$CHECK_ONLY" ] || exit $costatus
diff --git a/usr.sbin/sysrc/sysrc.8 b/usr.sbin/sysrc/sysrc.8
index 0a4aace2e861..6d53e19665cd 100644
--- a/usr.sbin/sysrc/sysrc.8
+++ b/usr.sbin/sysrc/sysrc.8
@@ -32,13 +32,13 @@
 .Nd safely edit system rc files
 .Sh SYNOPSIS
 .Nm
-.Op Fl dDeFhinNqvx
+.Op Fl cdDeFhinNqvx
 .Op Fl f Ar file
 .Op Fl j Ar jail | Fl R Ar dir
 .Ar name Ns Op = Ns Ar value
 .Ar ...
 .Nm
-.Op Fl dDeFhinNqvx
+.Op Fl cdDeFhinNqvx
 .Op Fl f Ar file
 .Op Fl j Ar jail | Fl R Ar dir
 .Fl a | A
@@ -57,6 +57,12 @@ Dump a list of all non-default configuration variables.
 .It Fl A
 Dump a list of all configuration variables
 .Pq incl. defaults .
+.It Fl c
+Check if the value will change when assigning a new value.
+If verbose
+.Pq see Dq Fl v
+prints a message stating whether a change would occur.
+Exits with success if no change is necessary, else returns error status.
 .It Fl d
 Print a description of the given variable.
 .It Fl D