Create new erlang .rel, .boot, .script files given an existing .rel file. Will create new files based on erlang VM this script is run in.

new_rel_file.escript

#!/usr/bin/env escript
%% -*- erlang -*-
%% Author: Drew Gulino
-module(new_rel_file).

-export([main/1]).

write_terms(Filename, List) ->
    Format = fun(Term) -> io_lib:format("~tp.~n", [Term]) end,
    Text = lists:map(Format, List),
    file:write_file(Filename, Text).

main([]) ->
  io:format("get_rel_update OLD_REL_FILENAME");
main(Args) ->
  OldRelFile = Args,
  %20.0+: Appname = hd(string:split(OldRelFile,"_")),
  Appname = lists:nth(1,string:tokens(OldRelFile,".")),
  io:format("Appname: ~p~n",[Appname]),
  {ok, Rel} = file:consult(OldRelFile),
  [{release,_,_Erts,Mods}] = Rel,
  L = lists:map(fun(M) -> element(1,M) end, Mods),
  lists:foreach(fun(M) -> application:load(M) end, L),
  Apps = application:loaded_applications(),
  As = [{Name,Version} || {Name,_,Version} <- Apps],
  NewErtsVersion = erlang:system_info(version),
  NewOtpRelease = erlang:system_info(otp_release),
  NewRel = {release, {"release",NewOtpRelease}, {erts,NewErtsVersion}, As},
  NewFilenameBase = Appname ++ "_" ++ NewErtsVersion,
  NewFilename = NewFilenameBase ++ ".rel",
  io:format("New Rel File: ~p~n",[NewFilename]),
  write_terms(NewFilename, [NewRel]),
  io:format("Creating .boot, .script~n"),
  Result = systools:make_script(NewFilenameBase, [local]),
  io:format("Result: ~p~n", [Result]).