[__group] Fall back to /etc files if getent(1) is not available

Some (embedded) systems (and Mac OS X) don't provide getent(1). The workaround
parses /etc/group under the assumption that the system only uses local users and
groups.

cdist/conf/type/__group/explorer/group

@@ -1,6 +1,7 @@
 #!/bin/sh
 #
 # 2011-2015 Steven Armstrong (steven-cdist at armstrong.cc)
+# 2019 Dennis Camera (dennis.camera at ssrq-sds-fds.ch)
 #
 # This file is part of cdist.
 #
@@ -21,7 +22,21 @@
 # Get an existing groups group entry.
 #
 
+not_supported() {
+	echo "Your operating system ($("$__explorer/os")) is currently not supported." >&2
+	echo "Cannot extract group information." >&2
+	echo "Please contribute an implementation for it if you can." >&2
+	exit 1
+}
+
 name=$__object_id
 
-getent group "$name" || true
-
+if command -v getent >/dev/null
+then
+	getent group "$name" || true
+elif [ -f /etc/group ]
+then
+	grep "^${name}:" /etc/group || true
+else
+	not_supported
+fi

cdist/conf/type/__group/explorer/gshadow

@@ -1,6 +1,7 @@
 #!/bin/sh
 #
 # 2011-2015 Steven Armstrong (steven-cdist at armstrong.cc)
+# 2019 Dennis Camera (dennis.camera at ssrq-sds-fds.ch)
 #
 # This file is part of cdist.
 #
@@ -22,13 +23,28 @@
 #
 
 name=$__object_id
-os="$("$__explorer/os")"
+os=$("$__explorer/os")
 
-case "$os" in
-    "freebsd"|"netbsd")
-	echo "$os does not have getent gshadow"
-	exit 0
-    ;;
+not_supported() {
+	echo "Your operating system ($os) is currently not supported." >&2
+	echo "Cannot extract group information." >&2
+	echo "Please contribute an implementation for it if you can." >&2
+	exit 1
+}
+
+case $os in
+	"freebsd"|"netbsd")
+		echo "$os does not have getent gshadow" >&2
+		exit 0
+	;;
 esac
 
-getent gshadow "$name" || true
+if command -v getent >/dev/null
+then
+	getent gshadow "$name" || true
+elif [ -f /etc/gshadow ]
+then
+	grep "^${name}:" /etc/gshadow || true
+else
+	not_supported
+fi