Optionally ignore missing files from CLI

This is particularly useful for wrapper scripts (like a `bin/dev`
https://stevenharman.net/bin-dev-for-heroku-local) trying to mimic
`dotenv-rails`'s ordered loading of multiple files.

README.md

@@ -76,12 +76,18 @@ Alternatively, you can use the `dotenv` executable to launch your application:
 $ dotenv ./script.rb
 ```
 
-The `dotenv` executable also accepts a single flag, `-f`. Its value should be a comma-separated list of configuration files, in the order of most important to least. All of the files must exist. There _must_ be a space between the flag and its value.
+The `dotenv` executable also accepts the flag `-f`. Its value should be a comma-separated list of configuration files, in the order of most important to least. All of the files must exist. There _must_ be a space between the flag and its value.
 
 ```console
 $ dotenv -f ".env.local,.env" ./script.rb
 ```
 
+The `dotenv` executable can optionally ignore missing files with the `-i` or `--ignore` flag. For example, if the `.env.local` file does not exist, the following will ignore the missing file and only load the `.env` file.
+
+```console
+$ dotenv -i -f ".env.local,.env" ./script.rb
+```
+
 To ensure `.env` is loaded in rake, load the tasks:
 
 ```ruby

lib/dotenv/cli.rb

@@ -11,6 +11,7 @@ class CLI < OptionParser
     def initialize(argv = [])
       @argv = argv.dup
       @filenames = []
+      @ignore = false
       @overload = false
 
       super "Usage: dotenv [options]"
@@ -20,6 +21,10 @@ def initialize(argv = [])
         @filenames = list
       end
 
+      on("-i", "--ignore", "ignore missing env files") do
+        @ignore = true
+      end
+
       on("-o", "--overload", "override existing ENV variables") do
         @overload = true
       end
@@ -43,11 +48,11 @@ def initialize(argv = [])
     end
 
     def run
-      if @overload
-        Dotenv.overload!(*@filenames)
-      else
-        Dotenv.load!(*@filenames)
-      end
+      meth = "load"
+      meth = "overload" if @overload
+      meth = "#{meth}!" unless @ignore
+
+      Dotenv.public_send(meth, *@filenames)
     rescue Errno::ENOENT => e
       abort e.message
     else

spec/dotenv/cli_spec.rb

@@ -28,6 +28,12 @@ def run(*args)
     end.to raise_error(SystemExit, /No such file/)
   end
 
+  it "ignores missing files when --ignore flag given" do
+    expect do
+      run "--ignore", "-f", ".doesnotexist"
+    end.not_to raise_error
+  end
+
   it "loads from multiple files specified by -f" do
     expect(ENV).not_to have_key("PLAIN")
     expect(ENV).not_to have_key("QUOTED")