Make pkg expressions more idiomatic, store scripts in separate files

packages/journalctl-last-invocation/package.nix

@@ -1,30 +1,32 @@
-{ pkgs, stdenvNoCC }:
+{
+	# Build tools.
+	installShellFiles, stdenvNoCC,
+
+	# Packages.
+	systemd, zsh,
+}:
 
-with pkgs;
 with stdenvNoCC;
 
 mkDerivation {
-	pname = "journalctl-last-invocation";
-	version = "2026-04-29";
+	name = "journalctl-last-invocation";
 
-	phases = [ "createSourcesPhase" "installPhase" ];
+	src = ./.;
 
-	createSourcesPhase = ''
-		# Same directory structure that `unpackPhase` would use.
-		mkdir -p /build/source
-
-		cat <<- EOF > /build/source/journalctl-last-invocation
-			#!${bash}/bin/sh
-
-			exec ${systemd}/bin/journalctl _SYSTEMD_INVOCATION_ID=\$(${systemd}/bin/systemctl show --value --property=InvocationID \$1)
-		EOF
-	'';
+	nativeBuildInputs = [ installShellFiles ];
+	buildInputs = [ zsh ];
 
 	installPhase = ''
-		mkdir -p $out/bin
+		runHook preInstall
 
-		cp /build/source/journalctl-last-invocation $out/bin/
+		installBin journalctl-last-invocation
 
-		chmod +x $out/bin/journalctl-last-invocation
+		runHook postInstall
+	'';
+
+	preFixup = ''
+		substituteInPlace $out/bin/journalctl-last-invocation \
+			--replace-fail journalctl ${systemd}/bin/journalctl \
+			--replace-fail systemctl ${systemd}/bin/systemctl
 	'';
 }