mailcap: add update script

pkgs/data/misc/mailcap/default.nix

@@ -1,4 +1,15 @@
-{ lib, stdenv, fetchurl }:
+{ lib
+, stdenv
+, fetchurl
+
+# updater
+, git
+, coreutils
+, gawk
+, gnused
+, writeScript
+, nix-update
+}:
 
 stdenv.mkDerivation rec {
   pname = "mailcap";
@@ -22,6 +33,17 @@ stdenv.mkDerivation rec {
     runHook postInstall
   '';
 
+  passthru.updateScript = writeScript "update-mailcap" ''
+    export PATH=${lib.makeBinPath [ git coreutils gawk gnused nix-update ]}:$PATH
+    VERSION="$(git ls-remote --tags --sort="v:refname" https://pagure.io/mailcap.git | \
+      awk '{ print $2 }' | \
+      grep "refs/tags/r" | \
+      sed -E -e "s,refs/tags/r(.*)$,\1," -e "s/-/./g" | \
+      sort --version-sort --reverse | \
+      head -n1)"
+    exec nix-update --version "$VERSION" "$@"
+  '';
+
   meta = with lib; {
     description = "Helper application and MIME type associations for file types";
     homepage = "https://pagure.io/mailcap";