cat: Use CLI::Parser to parse args

Library/Homebrew/cmd/cat.rb

@@ -1,16 +1,29 @@
 #:  * `cat` <formula>:
 #:    Display the source to <formula>.
 
+require "cli_parser"
+
 module Homebrew
   module_function
 
+  def cat_args
+    Homebrew::CLI::Parser.new do
+      usage_banner <<~EOS
+        `cat` <formula>
+
+        Display the source to <formula>.
+      EOS
+    end
+  end
+
   def cat
+    cat_args.parse
     # do not "fix" this to support multiple arguments, the output would be
     # unparsable, if the user wants to cat multiple formula they can call
     # brew cat multiple times.
     formulae = ARGV.formulae
     raise FormulaUnspecifiedError if formulae.empty?
-    raise "`brew cat` doesn't support multiple arguments" if formulae.size > 1
+    raise "`brew cat` doesn't support multiple arguments" if args.remaining.size > 1
 
     cd HOMEBREW_REPOSITORY
     exec "cat", formulae.first.path, *ARGV.options_only

Library/Homebrew/test/cmd/help_spec.rb

@@ -14,7 +14,7 @@ describe "brew", :integration_test do
 
     it "prints help for a documented Ruby command" do
       expect { brew "help", "cat" }
-        .to output(/^brew cat/).to_stdout
+        .to output(/^Usage: brew cat/).to_stdout
         .and be_a_success
     end
 
@@ -40,7 +40,7 @@ describe "brew", :integration_test do
   describe "cat" do
     it "prints help when no argument is given" do
       expect { brew "cat" }
-        .to output(/^brew cat/).to_stderr
+        .to output(/^Usage: brew cat/).to_stderr
         .and be_a_failure
     end
   end