Add warnings for 'exit' similar to 'return' (fixes #1388)

CHANGELOG.md

@@ -2,14 +2,17 @@
 ### Added
 - Command line option --severity/-S for filtering by minimum severity
 - Command line option --wiki-link-count/-W for showing wiki links
+- SC2152/SC2151: Warn about bad `exit` values like `1234` and `"foo"`
 - SC2236/SC2237: Suggest -n/-z instead of ! -z/-n
 - SC2238: Warn when redirecting to a known command name, e.g. ls > rm
 - SC2239: Warn if the shebang is not an absolute path, e.g. #!bin/sh
 - SC2240: Warn when passing additional arguments to dot (.) in sh/dash
 - SC1133: Better diagnostics when starting a line with |/||/&&
+
 ### Changed
 - Most warnings now have useful end positions
 - SC1117 about unknown double-quoted escape sequences has been retired
+
 ### Fixed
 - SC2021 no longer triggers for equivalence classes like '[=e=]'
 - SC2221/SC2222 no longer mistriggers on fall-through case branches

src/ShellCheck/Checks/Commands.hs

@@ -61,6 +61,7 @@ commandChecks = [
     ,checkGrepRe
     ,checkTrapQuotes
     ,checkReturn
+    ,checkExit
     ,checkFindExecWithSingleArgument
     ,checkUnusedEchoEscapes
     ,checkInjectableFindSh
@@ -281,15 +282,28 @@ prop_checkReturn4 = verifyNot checkReturn "return $((a|b))"
 prop_checkReturn5 = verify checkReturn "return -1"
 prop_checkReturn6 = verify checkReturn "return 1000"
 prop_checkReturn7 = verify checkReturn "return 'hello world'"
-checkReturn = CommandCheck (Exactly "return") (f . arguments)
+checkReturn = CommandCheck (Exactly "return") (returnOrExit
+        (\c -> err c 2151 "Only one integer 0-255 can be returned. Use stdout for other data.")
+        (\c -> err c 2152 "Can only return 0-255. Other data should be written to stdout."))
+
+prop_checkExit1 = verifyNot checkExit "exit"
+prop_checkExit2 = verifyNot checkExit "exit 1"
+prop_checkExit3 = verifyNot checkExit "exit $var"
+prop_checkExit4 = verifyNot checkExit "exit $((a|b))"
+prop_checkExit5 = verify checkExit "exit -1"
+prop_checkExit6 = verify checkExit "exit 1000"
+prop_checkExit7 = verify checkExit "exit 'hello world'"
+checkExit = CommandCheck (Exactly "exit") (returnOrExit
+        (\c -> err c 2241 "The exit status can only be one integer 0-255. Use stdout for other data.")
+        (\c -> err c 2242 "Can only exit with status 0-255. Other data should be written to stdout/stderr."))
+
+returnOrExit multi invalid = (f . arguments)
   where
     f (first:second:_) =
-        err (getId second) 2151
+        multi (getId first)
-            "Only one integer 0-255 can be returned. Use stdout for other data."
     f [value] =
         when (isInvalid $ literal value) $
-            err (getId value) 2152
+            invalid (getId value)
-                "Can only return 0-255. Other data should be written to stdout."
     f _ = return ()
 
     isInvalid s = s == "" || any (not . isDigit) s || length s > 5