metadata: Add --get (from bremner)

CmdLine/Usage.hs

@@ -73,6 +73,8 @@ paramNumRange :: String
 paramNumRange = "NUM|RANGE"
 paramRemote :: String
 paramRemote = "REMOTE"
+paramField :: String
+paramField = "FIELD"
 paramGlob :: String
 paramGlob = "GLOB"
 paramName :: String

Command/MetaData.hs

@@ -18,7 +18,7 @@ import qualified Data.Set as S
 import Data.Time.Clock.POSIX
 
 def :: [Command]
-def = [withOptions [setOption, tagOption, untagOption, jsonOption] $
+def = [withOptions [setOption, tagOption, untagOption, getOption, jsonOption] $
 	command "metadata" paramPaths seek
 	SectionMetaData "sets metadata of a file"]
 
@@ -31,6 +31,9 @@ setOption = Option ['s'] ["set"] (ReqArg mkmod "FIELD[+-]=VALUE") "set metadata"
   where
 	mkmod = either error storeModMeta . parseModMeta
 
+getOption :: Option
+getOption = fieldOption ['g'] "get" paramField "get single metadata field"
+
 tagOption :: Option
 tagOption = Option ['t'] ["tag"] (ReqArg mkmod "TAG") "set a tag"
   where
@@ -44,13 +47,20 @@ untagOption = Option ['u'] ["untag"] (ReqArg mkmod "TAG") "remove a tag"
 seek :: CommandSeek
 seek ps = do
 	modmeta <- Annex.getState Annex.modmeta
+	getfield <- getOptionField getOption $ \ms ->
+		return $ either error id . mkMetaField <$> ms
 	now <- liftIO getPOSIXTime
-	withFilesInGit (whenAnnexed $ start now modmeta) ps
+	withFilesInGit (whenAnnexed $ start now getfield modmeta) ps
 
-start :: POSIXTime -> [ModMeta] -> FilePath -> (Key, Backend) -> CommandStart
-start now ms file (k, _) = do
+start :: POSIXTime -> Maybe MetaField -> [ModMeta] -> FilePath -> (Key, Backend) -> CommandStart
+start now Nothing ms file (k, _) = do
 	showStart "metadata" file
 	next $ perform now ms k
+start _ (Just f) _ _ (k, _) = do
+	l <- S.toList . currentMetaDataValues f <$> getCurrentMetaData k
+	liftIO $ forM_ l $
+		putStrLn . fromMetaValue
+	stop
 
 perform :: POSIXTime -> [ModMeta] -> Key -> CommandPerform
 perform _ [] k = next $ cleanup k

debian/changelog

@@ -22,6 +22,7 @@ git-annex (5.20140307) UNRELEASED; urgency=medium
   * Avoid encoding errors when using the unused log file.
   * vicfg: Allows editing preferred content expressions for groups.
   * groupwanted can be used in preferred content expressions.
+  * metadata: Add --get
 
  -- Joey Hess <joeyh@debian.org>  Thu, 06 Mar 2014 16:17:01 -0400
 

doc/git-annex.mdwn

@@ -705,12 +705,20 @@ subdirectories).
 
 # METADATA COMMANDS
 
-* `metadata [path ...] [-s field=value -s field+=value -s field-=value ...]`
+* `metadata [path ...] [-s field=value -s field+=value -s field-=value ...] [-g field]`
 
   Each file can have any number of metadata fields attached to it,
-  which each in turn have any number of values. This sets metadata
-  for the specified file or files, or if run without any values, shows
-  the current metadata.
+  which each in turn have any number of values. 
+  
+  This command can be used to set metadata, or show the currently set
+  metadata.
+  
+  To show current metadata, run without any -s parameters. The --json
+  option will enable json output.
+
+  To only get the value(s) of a single field, use -g field.
+  The values will be output one per line, with no other output, so
+  this is suitable for use in a script.
 
   To set a field's value, removing any old value(s), use -s field=value.