add script-interpreter

script-interpreter.nix

@@ -0,0 +1,14 @@
+with builtins;
+
+let file-lines = import ./file-lines.nix; in
+
+f: ( let n = head (split-filename f); in
+    let
+      lines = file-lines f;
+      firstLine = head lines;
+      shebangMatch = match ''#! *(.*[/])?(([\][ ]|[^ /])*)( (.*))?'' firstLine;
+    in
+      if shebangMatch == null
+        then rec { interpreter = "sh"; args = "";}
+        else rec { interpreter = (elemAt shebangMatch 1); args = (elemAt shebangMatch 4);}
+  )