Don't suggest grep -c when used with -o

ShellCheck/ASTLib.hs

@@ -211,14 +211,19 @@ braceExpand (T_NormalWord id list) = take 1000 $ do
         braceExpand item
     part x = return x
 
--- Maybe get the command name of a token representing a command
-getCommandName t =
+-- Maybe get a SimpleCommand from immediate wrappers like T_Redirections
+getCommand t =
     case t of
-        T_Redirecting _ _ w -> getCommandName w
-        T_SimpleCommand _ _ (w:_) -> getLiteralString w
-        T_Annotation _ _ t -> getCommandName t
+        T_Redirecting _ _ w -> getCommand w
+        T_SimpleCommand _ _ (w:_) -> return t
+        T_Annotation _ _ t -> getCommand t
         otherwise -> Nothing
 
+-- Maybe get the command name of a token representing a command
+getCommandName t = do
+    (T_SimpleCommand _ _ (w:_)) <- getCommand t
+    getLiteralString w
+
 -- If a command substitution is a single command, get its name.
 --  $(date +%s) = Just "date"
 getCommandNameFromExpansion :: Token -> Maybe String

ShellCheck/Analytics.hs

@@ -371,6 +371,8 @@ prop_checkPipePitfalls4 = verifyNot checkPipePitfalls "find . -print0 | xargs -0
 prop_checkPipePitfalls5 = verifyNot checkPipePitfalls "ls -N | foo"
 prop_checkPipePitfalls6 = verify checkPipePitfalls "find . | xargs foo"
 prop_checkPipePitfalls7 = verifyNot checkPipePitfalls "find . -printf '%s\\n' | xargs foo"
+prop_checkPipePitfalls8 = verify checkPipePitfalls "foo | grep bar | wc -l"
+prop_checkPipePitfalls9 = verifyNot checkPipePitfalls "foo | grep -o bar | wc -l"
 checkPipePitfalls _ (T_Pipeline id _ commands) = do
     for ["find", "xargs"] $
         \(find:xargs:_) ->
@@ -390,8 +392,12 @@ checkPipePitfalls _ (T_Pipeline id _ commands) = do
     for' ["ps", "grep"] $
         \x -> info x 2009 "Consider using pgrep instead of grepping ps output."
 
-    for' ["grep", "wc"] $
-        \x -> style x 2126 "Consider using grep -c instead of grep|wc."
+    for ["grep", "wc"] $
+        \(grep:wc:_) ->
+            let flags = fromMaybe [] $ map snd <$> getAllFlags <$> getCommand grep
+            in
+                unless (any (`elem` ["o", "only-matching"]) flags) $
+                    style (getId grep) 2126 "Consider using grep -c instead of grep|wc."
 
     didLs <- liftM or . sequence $ [
         for' ["ls", "grep"] $