Check for multiline shebang script hacks

Fixes #8

lib/linguist/blob_helper.rb

@@ -308,7 +308,7 @@ module Linguist
       # Fail fast if blob isn't viewable?
       return unless viewable?
 
-      if data && (match = data.match(/(.+)\n?/)) && (bang = match[0]) =~ /^#!/
+      if data && (match = lines[0].match(/(.+)\n?/)) && (bang = match[0]) =~ /^#!/
         bang.sub!(/^#! /, '#!')
         tokens = bang.split(' ')
         pieces = tokens.first.split('/')
@@ -325,6 +325,16 @@ module Linguist
           script.sub! $1, ''
         end
 
+        # Check for multiline shebang hacks that exec themselves
+        #
+        #   #!/bin/sh
+        #   exec foo "$0" "$@"
+        #
+        if script == 'sh' &&
+            lines[0...5].any? { |l| l.match(/exec (\w+).+\$0.+\$@/) }
+          script = $1
+        end
+
         script
       end
     end

test/fixtures/script.rkt

@@ -0,0 +1,7 @@
+#!/bin/sh
+#| -*- scheme -*-
+exec racket -um "$0" "$@"
+|#
+
+(require racket/file racket/path racket/list racket/string
+         (for-syntax racket/base))

test/fixtures/script.scala

@@ -0,0 +1,9 @@
+#!/bin/sh
+exec scala "$0" "$@"
+!#
+
+object HelloWorld {
+  def main(args: Array[String]) {
+    println("Hello, world!")
+  }
+}

test/test_blob.rb

@@ -286,6 +286,8 @@ class TestBlob < Test::Unit::TestCase
     assert_equal 'rake', blob("script.rake").shebang_script
     assert_equal 'foo', blob("script.foo").shebang_script
     assert_equal 'nush', blob("script.nu").shebang_script
+    assert_equal 'scala', blob("script.scala").shebang_script
+    assert_equal 'racket', blob("script.rkt").shebang_script
     assert_equal nil, blob("foo.rb").shebang_script
   end
 
@@ -301,6 +303,8 @@ class TestBlob < Test::Unit::TestCase
     assert_equal Language['Ruby'], blob("script.mrb").shebang_language
     assert_equal Language['Ruby'], blob("script.rake").shebang_language
     assert_equal Language['Nu'], blob("script.nu").shebang_language
+    assert_equal Language['Scala'], blob("script.scala").shebang_language
+    assert_equal Language['Racket'], blob("script.rkt").shebang_language
     assert_equal nil, blob("script.foo").shebang_language
     assert_equal nil, blob("foo.rb").shebang_language
   end