Added checks for multiple pipe combinations.

ShellCheck/Analytics.hs

@@ -40,6 +40,7 @@ checkList l t m = foldl (\x f -> f t x) m l
 runBasicAnalysis f t m = snd $ runState (doAnalysis f t) m
 basicChecks = [
     checkUuoc
+    ,checkPipePitfalls
     ,checkForInQuoted
     ,checkForInLs
     ,checkUnquotedExpansions
@@ -115,6 +116,35 @@ checkUuoc (T_Pipeline _ (T_Redirecting _ _ f@(T_SimpleCommand id _ _):_:_)) =
                          _ -> return ()
 checkUuoc _ = return ()
 
+prop_checkPipePitfalls1 = verify checkPipePitfalls "foo | grep foo | awk bar"
+prop_checkPipePitfalls2 = verifyNot checkPipePitfalls "foo | awk bar | grep foo"
+prop_checkPipePitfalls3 = verify checkPipePitfalls "ls | grep -v mp3"
+checkPipePitfalls (T_Pipeline id commands) = do
+    for [["grep"], ["awk"]] $  \id -> style id "You don't need grep | awk, awk can filter lines by itself."
+    for [["ls"], ["?"]] $      \id -> warn id "Don't parse ls output; it mangles filenames."
+    for [["ls"], ["grep"]] $   \id -> warn id "Don't use ls | grep. Use a for loop with a condition in it."
+    for [["ls"], ["xargs"]] $  \id -> warn id "Don't use ls | xargs. Use find -exec .. +"
+    for [["find"], ["xargs"]]$ \id -> warn id "Don't use find | xargs cmd. find -exec cmd {} + handles whitespace."
+    for [["?"], ["echo"]] $    \id -> info id "echo doesn't read from stdin, are you sure you should be piping to it?"
+  where
+    for l f =
+        let indices = indexOfSublists l (map (take 1 . deadSimple) commands)
+        in mapM_ f (map (\n -> getId $ commands !! n) indices)
+checkPipePitfalls _ = return ()
+
+indexOfSublists sub all = f 0 all
+  where
+    f _ [] = []
+    f n a@(r:rest) =
+        let others = f (n+1) rest in
+            if match sub (take (length sub) a)
+              then n:others
+              else others
+    match [] [] = True
+    match (["?"]:r1) (_:r2) = match r1 r2
+    match (x1:r1) (x2:r2) | x1 == x2 = match r1 r2
+    match _ _ = False
+
 
 isMagicInQuotes (T_DollarBraced _ s) | '@' `elem` s = True
 isMagicInQuotes _ = False