Added 'spec --property' option

README.md

@@ -77,7 +77,7 @@ SEARCH_TERM and only matching items are shown.
 This is an alias for `agner list -s`
 
     agner spec PACKAGE [-v/--version package_version] [-b/--browser] 
-                       [-h/--homepage]
+                       [-h/--homepage] [-p/--property PROPERTY]
 
 Will print a specification of a given package on stdout. If the
 optional version constraint is given (for example `agner spec gproc -v
@@ -90,6 +90,9 @@ file in its respective `.agner` repository.
 If `-h` or `--homepage` is present, it will also open browser with the package's
 homepage.
 
+If `-p` or `--property` is supplied, agner will only render particular PROPERTY value
+instead of a full specification (example: `agner spec -p rebar_compatible yaws`).
+
     agner fetch PACKAGE [DESTDIR] [-v/--version package_version] [-c/--compile]
                                   [-a/--add-path]
 

src/agner_main.erl

@@ -25,7 +25,8 @@ arg_proplist() ->
 		{package, undefined, undefined, string, "Package name"},
 		{browser, $b, "browser", boolean, "Show specification in the browser"},
 		{homepage, $h, "homepage", boolean, "Show package homepage in the browser"},
-		{version, $v, "version", {string, "@master"}, "Version"}
+		{version, $v, "version", {string, "@master"}, "Version"},
+        {property, $p, "property", string, "Particular property to render instead of a full spec"}
 	   ]}},
 	 {"versions",
 	  {versions,
@@ -133,7 +134,12 @@ handle_command(spec, Opts) ->
                 _ ->
                     ignore
             end,
-            io:format("~p~n",[Spec])
+            case proplists:get_value(property, Opts) of
+                undefined ->
+                    io:format("~p~n",[Spec]);
+                Property ->
+                    io:format("~s~n",[agner_spec:property_to_list(lists:keyfind(list_to_atom(Property), 1, Spec))])
+            end
     end;
 
 handle_command(versions, Opts) ->

src/agner_spec.erl

@@ -1,7 +1,7 @@
 %% -*- Mode: Erlang; tab-width: 4 -*-
 -module(agner_spec).
 -include_lib("agner.hrl").
--export([parse/1, list_to_version/2, version_to_list/1]).
+-export([parse/1, list_to_version/2, version_to_list/1, property_to_list/1]).
 
 -type agner_spec_source() :: string().
 
@@ -45,3 +45,14 @@ version_to_list({flavour, Version}) ->
     "@" ++ Version;
 version_to_list({release, Version}) ->
     Version.
+
+-spec property_to_list(agner_spec_property()) -> string().
+
+property_to_list({_,V}) when is_list(V) ->
+    io_lib:format("~s", [V]);
+property_to_list(Prop) when is_tuple(Prop) ->
+    io_lib:format("~p",[list_to_tuple(tl(tuple_to_list(Prop)))]);
+property_to_list(undefined) ->
+    "".
+
+