Add SC2239: shebang is not absolute path.

CHANGELOG.md

@@ -4,6 +4,7 @@
 - Command line option --wiki-link-count/-W for showing wiki links
 - 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
 ### Changed
 - Most warnings now have useful end positions
 - SC1117 about unknown double-quoted escape sequences has been retired

src/ShellCheck/Analytics.hs

@@ -432,17 +432,22 @@ prop_checkShebang4 = verifyNotTree checkShebang "#shellcheck shell=sh\nfoo"
 prop_checkShebang5 = verifyTree checkShebang "#!/usr/bin/env ash"
 prop_checkShebang6 = verifyNotTree checkShebang "#!/usr/bin/env ash\n# shellcheck shell=dash\n"
 prop_checkShebang7 = verifyNotTree checkShebang "#!/usr/bin/env ash\n# shellcheck shell=sh\n"
+prop_checkShebang8 = verifyTree checkShebang "#!bin/sh\ntrue"
+prop_checkShebang9 = verifyNotTree checkShebang "# shellcheck shell=sh\ntrue"
+prop_checkShebang10= verifyNotTree checkShebang "#!foo\n# shellcheck shell=sh ignore=SC2239\ntrue"
 checkShebang params (T_Annotation _ list t) =
     if any isOverride list then [] else checkShebang params t
   where
     isOverride (ShellOverride _) = True
     isOverride _ = False
-checkShebang params (T_Script id sb _) = execWriter $
+checkShebang params (T_Script id sb _) = execWriter $ do
     unless (shellTypeSpecified params) $ do
         when (sb == "") $
             err id 2148 "Tips depend on target shell and yours is unknown. Add a shebang."
         when (executableFromShebang sb == "ash") $
             warn id 2187 "Ash scripts will be checked as Dash. Add '# shellcheck shell=dash' to silence."
+    unless (null sb || "/" `isPrefixOf` sb) $
+        err id 2239 "Ensure the shebang uses an absolute path to the interpreter."
 
 
 prop_checkForInQuoted = verify checkForInQuoted "for f in \"$(ls)\"; do echo foo; done"