diff --git a/src/ShellCheck/ASTLib.hs b/src/ShellCheck/ASTLib.hs
index 6cf48cb..aa73c79 100644
--- a/src/ShellCheck/ASTLib.hs
+++ b/src/ShellCheck/ASTLib.hs
@@ -544,33 +544,18 @@ getCommandNameAndToken direct t = fromMaybe (Nothing, t) $ do
                     return t
                 _ -> fail ""
 
--- If a command substitution is a single command, get its name.
---  $(date +%s) = Just "date"
-getCommandNameFromExpansion :: Token -> Maybe String
-getCommandNameFromExpansion t =
+-- If a command substitution is a single SimpleCommand, return it.
+getSimpleCommandFromExpansion :: Token -> Maybe Token
+getSimpleCommandFromExpansion t =
     case t of
         T_DollarExpansion _ [c] -> extract c
         T_Backticked _ [c] -> extract c
         T_DollarBraceCommandExpansion _ [c] -> extract c
         _ -> Nothing
   where
-    extract (T_Pipeline _ _ [cmd]) = getCommandName cmd
+    extract (T_Pipeline _ _ [c]) = getCommand c
     extract _ = Nothing
 
--- If a command substitution is a single command, get its argument Tokens.
--- Return an empty list if there are no arguments or the token is not a command substitution.
--- $(date +%s) = ["+%s"]
-getArgumentsFromExpansion :: Token -> [Token]
-getArgumentsFromExpansion t =
-    case t of
-        T_DollarExpansion _ [c] -> extract c
-        T_Backticked _ [c] -> extract c
-        T_DollarBraceCommandExpansion _ [c] -> extract c
-        _ -> []
-  where
-    extract (T_Pipeline _ _ [cmd]) = arguments cmd
-    extract _ = []
-
 -- Get the basename of a token representing a command
 getCommandBasename = fmap basename . getCommandName
 
@@ -928,5 +913,20 @@ getEnableDirectives root =
         T_Annotation _ list _ -> [s | EnableComment s <- list]
         _ -> []
 
+
+commandExpansionShouldBeSplit t = do
+    cmd <- getSimpleCommandFromExpansion t
+    name <- getCommandName cmd
+    case () of
+        -- Should probably be split
+        _ | name `elem` ["seq", "pgrep"] -> return True
+        -- Portage macros that return a single word or nothing
+        _ | name `elem` ["usev", "use_with", "use_enable"] -> return True
+        -- Portage macros that are fine as long as the arguments have no spaces
+        _ | name `elem` ["usex", "meson_use", "meson_feature"] -> do
+            return . not $ any (' ' `elem`) $ map (getLiteralStringDef " ") $ arguments cmd
+        _ -> Nothing
+
+
 return []
 runTests = $quickCheckAll
diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index 58c3310..51015d2 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -792,6 +792,11 @@ prop_checkUnquotedExpansions8 = verifyNot checkUnquotedExpansions "set -- $(seq
 prop_checkUnquotedExpansions9 = verifyNot checkUnquotedExpansions "echo foo `# inline comment`"
 prop_checkUnquotedExpansions10 = verify checkUnquotedExpansions "#!/bin/sh\nexport var=$(val)"
 prop_checkUnquotedExpansions11 = verifyNot checkUnquotedExpansions "ps -p $(pgrep foo)"
+prop_checkUnquotedExpansions12 = verify checkUnquotedExpansions "#!/bin/sh\nexport var=$(val)"
+prop_checkUnquotedExpansions13 = verifyNot checkUnquotedExpansions "echo $(usev X)"
+prop_checkUnquotedExpansions14 = verifyNot checkUnquotedExpansions "echo $(usex X \"\" Y)"
+prop_checkUnquotedExpansions15 = verify checkUnquotedExpansions "echo $(usex X \"Y Z\" W)"
+
 checkUnquotedExpansions params =
     check
   where
@@ -801,12 +806,9 @@ checkUnquotedExpansions params =
     check _ = return ()
     tree = parentMap params
     examine t contents =
-        unless (null contents || shouldBeSplit t || isQuoteFree (shellType params) tree t || usedAsCommandName tree t) $
+        unless (null contents || commandExpansionShouldBeSplit t == Just True || isQuoteFree (shellType params) tree t || usedAsCommandName tree t) $
             warn (getId t) 2046 "Quote this to prevent word splitting."
 
-    shouldBeSplit t =
-        getCommandNameFromExpansion t `elem` [Just "seq", Just "pgrep"]
-
 
 prop_checkRedirectToSame = verify checkRedirectToSame "cat foo > foo"
 prop_checkRedirectToSame2 = verify checkRedirectToSame "cat lol | sed -e 's/a/b/g' > lol"
@@ -1037,9 +1039,6 @@ checkStderrRedirect params redir@(T_Redirecting _ [
 
 checkStderrRedirect _ _ = return ()
 
-lt x = trace ("Tracing " ++ show x) x -- STRIP
-ltt t = trace ("Tracing " ++ show t)  -- STRIP
-
 
 prop_checkSingleQuotedVariables  = verify checkSingleQuotedVariables "echo '$foo'"
 prop_checkSingleQuotedVariables2 = verify checkSingleQuotedVariables "echo 'lol$1.jpg'"
@@ -1070,6 +1069,10 @@ prop_checkSingleQuotedVariables22 = verifyNot checkSingleQuotedVariables "jq '$_
 prop_checkSingleQuotedVariables23 = verifyNot checkSingleQuotedVariables "command jq '$__loc__'"
 prop_checkSingleQuotedVariables24 = verifyNot checkSingleQuotedVariables "exec jq '$__loc__'"
 prop_checkSingleQuotedVariables25 = verifyNot checkSingleQuotedVariables "exec -c -a foo jq '$__loc__'"
+prop_checkSingleQuotedVariablesCros1 = verifyNot checkSingleQuotedVariables "python_gen_any_dep 'dev-python/pyyaml[${PYTHON_USEDEP}]'"
+prop_checkSingleQuotedVariablesCros2 = verifyNot checkSingleQuotedVariables "python_gen_cond_dep 'dev-python/unittest2[${PYTHON_USEDEP}]' python2_7 pypy"
+prop_checkSingleQuotedVariablesCros3 = verifyNot checkSingleQuotedVariables "version_format_string '${PN}_source_$1_$2-$3_$4'"
+
 
 
 checkSingleQuotedVariables params t@(T_SingleQuoted id s) =
@@ -1109,6 +1112,9 @@ checkSingleQuotedVariables params t@(T_SingleQuoted id s) =
                 ,"git filter-branch"
                 ,"mumps -run %XCMD"
                 ,"mumps -run LOOP%XCMD"
+                ,"python_gen_any_dep"
+                ,"python_gen_cond_dep"
+                ,"version_format_string"
                 ]
             || "awk" `isSuffixOf` commandName
             || "perl" `isPrefixOf` commandName
@@ -3509,6 +3515,7 @@ prop_checkSplittingInArrays5 = verifyNot checkSplittingInArrays "a=( $! $$ $# )"
 prop_checkSplittingInArrays6 = verifyNot checkSplittingInArrays "a=( ${#arr[@]} )"
 prop_checkSplittingInArrays7 = verifyNot checkSplittingInArrays "a=( foo{1,2} )"
 prop_checkSplittingInArrays8 = verifyNot checkSplittingInArrays "a=( * )"
+prop_checkSplittingInArrays9 = verifyNot checkSplittingInArrays "a=( $(use_enable foo) )"
 checkSplittingInArrays params t =
     case t of
         T_Array _ elements -> mapM_ check elements
@@ -3518,6 +3525,7 @@ checkSplittingInArrays params t =
         T_NormalWord _ parts -> mapM_ checkPart parts
         _ -> return ()
     checkPart part = case part of
+        _ | commandExpansionShouldBeSplit part == Just True -> return ()
         T_DollarExpansion id _ -> forCommand id
         T_DollarBraceCommandExpansion id _ -> forCommand id
         T_Backticked id _ -> forCommand id
diff --git a/src/ShellCheck/AnalyzerLib.hs b/src/ShellCheck/AnalyzerLib.hs
index 3ceb245..28cbf1b 100644
--- a/src/ShellCheck/AnalyzerLib.hs
+++ b/src/ShellCheck/AnalyzerLib.hs
@@ -604,6 +604,17 @@ getReferencedVariableCommand base@(T_SimpleCommand _ _ (T_NormalWord _ (T_Litera
                 head:_ -> map (\x -> (base, head, x)) $ getVariablesFromLiteralToken head
                 _ -> []
         "alias" -> [(base, token, name) | token <- rest, name <- getVariablesFromLiteralToken token]
+
+        -- tc-export makes a list of toolchain variables available, similar to export.
+        -- Usage tc-export CC CXX
+        "tc-export" -> concatMap getReference rest
+
+        -- tc-export_build_env exports the listed variables plus a bunch of BUILD_XX variables.
+        -- Usage tc-export_build_env BUILD_CC
+        "tc-export_build_env" ->
+            concatMap getReference rest
+                ++ [ (base, base, v) | v <- portageBuildEnvVariables ]
+
         _ -> []
   where
     forDeclare =
@@ -675,6 +686,16 @@ getModifiedVariableCommand base@(T_SimpleCommand id cmdPrefix (T_NormalWord _ (T
         "DEFINE_integer" -> maybeToList $ getFlagVariable rest
         "DEFINE_string" -> maybeToList $ getFlagVariable rest
 
+        "tc-export" -> concatMap getModifierParamString rest
+
+        -- tc-export_build_env exports the listed variables plus a bunch of BUILD_XX variables.
+        -- Usage tc-export_build_env BUILD_CC
+        "tc-export_build_env" ->
+            concatMap getModifierParamString rest
+                ++ [ (base, base, var, DataString $ SourceExternal) |
+                        var <- ["BUILD_" ++ x, x ++ "_FOR_BUILD" ],
+                        x <- portageBuildEnvVariables ]
+
         _ -> []
   where
     flags = map snd $ getAllFlags base
diff --git a/src/ShellCheck/Data.hs b/src/ShellCheck/Data.hs
index 550ff87..fff27be 100644
--- a/src/ShellCheck/Data.hs
+++ b/src/ShellCheck/Data.hs
@@ -62,8 +62,92 @@ internalVariables = [
     , "FLAGS_ARGC", "FLAGS_ARGV", "FLAGS_ERROR", "FLAGS_FALSE", "FLAGS_HELP",
     "FLAGS_PARENT", "FLAGS_RESERVED", "FLAGS_TRUE", "FLAGS_VERSION",
     "flags_error", "flags_return"
+  ] ++ portageManualInternalVariables
+
+
+portageManualInternalVariables = [
+    -- toolchain settings
+    "CFLAGS", "CXXFLAGS", "CPPFLAGS", "LDFLAGS", "FFLAGS", "FCFLAGS",
+    "CBUILD", "CHOST", "MAKEOPTS",
+    -- TODO: Delete these if we can handle `tc-export CC` implicit export.
+    "CC", "CPP", "CXX",
+
+    -- portage internals
+    "EBUILD_PHASE", "EBUILD_SH_ARGS", "EMERGE_FROM", "FILESDIR",
+    "MERGE_TYPE", "PM_EBUILD_HOOK_DIR", "PORTAGE_ACTUAL_DISTDIR",
+    "PORTAGE_ARCHLIST", "PORTAGE_BASHRC", "PORTAGE_BINPKG_FILE",
+    "PORTAGE_BINPKG_TAR_OPTS", "PORTAGE_BINPKG_TMPFILE", "PORTAGE_BIN_PATH",
+    "PORTAGE_BUILDDIR", "PORTAGE_BUILD_GROUP", "PORTAGE_BUILD_USER",
+    "PORTAGE_BUNZIP2_COMMAND", "PORTAGE_BZIP2_COMMAND", "PORTAGE_COLORMAP",
+    "PORTAGE_CONFIGROOT", "PORTAGE_DEBUG", "PORTAGE_DEPCACHEDIR",
+    "PORTAGE_EBUILD_EXIT_FILE", "PORTAGE_ECLASS_LOCATIONS", "PORTAGE_GID",
+    "PORTAGE_GRPNAME", "PORTAGE_INST_GID", "PORTAGE_INST_UID",
+    "PORTAGE_INTERNAL_CALLER", "PORTAGE_IPC_DAEMON", "PORTAGE_IUSE",
+    "PORTAGE_LOG_FILE", "PORTAGE_MUTABLE_FILTERED_VARS",
+    "PORTAGE_OVERRIDE_EPREFIX", "PORTAGE_PYM_PATH", "PORTAGE_PYTHON",
+    "PORTAGE_PYTHONPATH", "PORTAGE_READONLY_METADATA", "PORTAGE_READONLY_VARS",
+    "PORTAGE_REPO_NAME", "PORTAGE_REPOSITORIES", "PORTAGE_RESTRICT",
+    "PORTAGE_SAVED_READONLY_VARS", "PORTAGE_SIGPIPE_STATUS", "PORTAGE_TMPDIR",
+    "PORTAGE_UPDATE_ENV", "PORTAGE_USERNAME", "PORTAGE_VERBOSE",
+    "PORTAGE_WORKDIR_MODE", "PORTAGE_XATTR_EXCLUDE", "REPLACING_VERSIONS",
+    "REPLACED_BY_VERSION", "__PORTAGE_HELPER", "__PORTAGE_TEST_HARDLINK_LOCKS",
+
+    -- generic ebuilds
+    "A", "ARCH", "BDEPEND", "BOARD_USE", "BROOT", "CATEGORY", "D",
+    "DEFINED_PHASES", "DEPEND", "DESCRIPTION", "DISTDIR", "DOCS", "EAPI",
+    "ECLASS", "ED", "EPREFIX", "EROOT", "ESYSROOT", "EXTRA_ECONF",
+    "EXTRA_EINSTALL", "EXTRA_MAKE", "FEATURES", "FILESDIR", "HOME", "HOMEPAGE",
+    "HTML_DOCS", "INHERITED", "IUSE", "KEYWORDS", "LICENSE", "P", "PATCHES",
+    "PDEPEND", "PF", "PKG_INSTALL_MASK", "PKGUSE", "PN", "PR", "PROPERTIES",
+    "PROVIDES_EXCLUDE", "PV", "PVR", "QA_AM_MAINTAINER_MODE",
+    "QA_CONFIGURE_OPTIONS", "QA_DESKTOP_FILE", "QA_DT_NEEDED", "QA_EXECSTACK",
+    "QA_FLAGS_IGNORED", "QA_MULTILIB_PATHS", "QA_PREBUILT", "QA_PRESTRIPPED",
+    "QA_SONAME", "QA_SONAME_NO_SYMLINK", "QA_TEXTRELS", "QA_WX_LOAD", "RDEPEND",
+    "REPOSITORY", "REQUIRED_USE", "REQUIRES_EXCLUDE", "RESTRICT", "ROOT", "S",
+    "SLOT", "SRC_TEST", "SRC_URI", "STRIP_MASK", "SUBSLOT", "SYSROOT", "T",
+    "WORKDIR",
+
+    -- autotest.eclass declared incorrectly
+    "AUTOTEST_CLIENT_TESTS", "AUTOTEST_CLIENT_SITE_TESTS",
+    "AUTOTEST_SERVER_TESTS", "AUTOTEST_SERVER_SITE_TESTS", "AUTOTEST_CONFIG",
+    "AUTOTEST_DEPS", "AUTOTEST_PROFILERS", "AUTOTEST_CONFIG_LIST",
+    "AUTOTEST_DEPS_LIST", "AUTOTEST_PROFILERS_LIST",
+
+    -- cros-board.eclass declared incorrectly
+    "CROS_BOARDS",
+
+    -- Undeclared cros-kernel2 vars
+    "AFDO_PROFILE_VERSION",
+
+    -- haskell-cabal.eclass declared incorrectly
+    "CABAL_FEATURES",
+
+    -- Undeclared haskell-cabal.eclass vars
+    "CABAL_CORE_LIB_GHC_PV",
+
+    -- Undeclared readme.gentoo.eclass vars
+    "DOC_CONTENTS",
+
+    -- Backwards compatibility perl-module.eclass vars
+    "MODULE_AUTHOR", "MODULE_VERSION",
+
+    -- Undeclared perl-module.eclass vars
+    "mydoc",
+
+    -- python-utils-r1.eclass declared incorrectly
+    "RESTRICT_PYTHON_ABIS", "PYTHON_MODNAME",
+
+    -- ABI variables
+    "ABI", "DEFAULT_ABI",
+
+    -- AFDO variables
+    "AFDO_LOCATION",
+
+    -- Linguas
+    "LINGUAS"
   ]
 
+
 specialIntegerVariables = [
     "$", "?", "!", "#"
   ]
@@ -90,7 +174,9 @@ unbracedVariables = specialVariables ++ [
 arrayVariables = [
     "BASH_ALIASES", "BASH_ARGC", "BASH_ARGV", "BASH_CMDS", "BASH_LINENO",
     "BASH_REMATCH", "BASH_SOURCE", "BASH_VERSINFO", "COMP_WORDS", "COPROC",
-    "DIRSTACK", "FUNCNAME", "GROUPS", "MAPFILE", "PIPESTATUS", "COMPREPLY"
+    "DIRSTACK", "FUNCNAME", "GROUPS", "MAPFILE", "PIPESTATUS", "COMPREPLY",
+    -- For Portage
+    "PATCHES"
   ]
 
 commonCommands = [
@@ -150,6 +236,11 @@ unaryTestOps = [
     "-o", "-v", "-R"
   ]
 
+-- Variables inspected by Portage tc-export_build_env
+portageBuildEnvVariables = [
+    "CFLAGS", "CXXFLAGS", "CPPFLAGS", "LDFLAGS"
+  ]
+
 shellForExecutable :: String -> Maybe Shell
 shellForExecutable name =
     case name of