diff --git a/Library/Homebrew/cask/lib/hbc/system_command.rb b/Library/Homebrew/cask/lib/hbc/system_command.rb
index e5a7d9202b..0c6f0eb367 100644
--- a/Library/Homebrew/cask/lib/hbc/system_command.rb
+++ b/Library/Homebrew/cask/lib/hbc/system_command.rb
@@ -25,11 +25,11 @@ module Hbc
       each_output_line do |type, line|
         case type
         when :stdout
+          puts line.chomp if print_stdout?
           processed_output[:stdout] << line
-          ohai line.chomp if print_stdout?
         when :stderr
+          $stderr.puts Formatter.error(line.chomp) if print_stderr?
           processed_output[:stderr] << line
-          ohai line.chomp if print_stderr?
         end
       end
 
@@ -100,17 +100,23 @@ module Hbc
 
     def each_line_from(sources)
       loop do
-        readable_sources = IO.select(sources)[0]
-        readable_sources.delete_if(&:eof?).first(1).each do |source|
-          type = ((source == sources[0]) ? :stdout : :stderr)
+        readable_sources, = IO.select(sources)
+
+        readable_sources = readable_sources.reject(&:eof?)
+
+        break if readable_sources.empty?
+
+        readable_sources.each do |source|
           begin
-            yield(type, source.readline_nonblock || "")
+            line = source.readline_nonblock || ""
+            type = (source == sources[0]) ? :stdout : :stderr
+            yield(type, line)
           rescue IO::WaitReadable, EOFError
             next
           end
         end
-        break if readable_sources.empty?
       end
+
       sources.each(&:close_read)
     end
 
diff --git a/Library/Homebrew/rubocops/extend/formula_cop.rb b/Library/Homebrew/rubocops/extend/formula_cop.rb
index 02bbb7c6d9..362a5134c0 100644
--- a/Library/Homebrew/rubocops/extend/formula_cop.rb
+++ b/Library/Homebrew/rubocops/extend/formula_cop.rb
@@ -460,7 +460,7 @@ module RuboCop
         when :str
           node.str_content
         when :dstr
-          node.each_child_node(:str).map(&:str_content).join("")
+          node.each_child_node(:str).map(&:str_content).join
         when :const
           node.const_name
         when :sym
diff --git a/Library/Homebrew/test/cask/download_strategy_spec.rb b/Library/Homebrew/test/cask/download_strategy_spec.rb
index ed8cd01ef6..3a69edaaf4 100644
--- a/Library/Homebrew/test/cask/download_strategy_spec.rb
+++ b/Library/Homebrew/test/cask/download_strategy_spec.rb
@@ -148,7 +148,7 @@ describe "download strategies", :cask do
           "DBw2KdR24q9t1wfjS9LUzelf5TWk6ojj8p9%2FHjl%2Fi%2FVCXN",
           "N4o1mW%2FMayy2tTY1qcC%2FTmqI1ulZS8SNuaSgr9Iys9oDF1%2",
           "BPK%2B4Sg==",
-        ].join("")
+        ].join
       end
 
       describe "#tarball_path" do
diff --git a/Library/Homebrew/test/cask/dsl_spec.rb b/Library/Homebrew/test/cask/dsl_spec.rb
index 67fcb027a8..2500a53fa3 100644
--- a/Library/Homebrew/test/cask/dsl_spec.rb
+++ b/Library/Homebrew/test/cask/dsl_spec.rb
@@ -20,7 +20,7 @@ describe Hbc::DSL, :cask do
     }
 
     it "prints a warning that it has encountered an unexpected method" do
-      expected = Regexp.compile(<<~EOS.lines.map(&:chomp).join(""))
+      expected = Regexp.compile(<<~EOS.lines.map(&:chomp).join)
         (?m)
         Warning:
         .*
diff --git a/Library/Homebrew/test/cask/pkg_spec.rb b/Library/Homebrew/test/cask/pkg_spec.rb
index f92d6854e2..6a7247058e 100644
--- a/Library/Homebrew/test/cask/pkg_spec.rb
+++ b/Library/Homebrew/test/cask/pkg_spec.rb
@@ -134,7 +134,7 @@ describe Hbc::Pkg, :cask do
           <string>#{volume}</string>
           <key>paths</key>
           <dict>
-            #{(pkg_files + pkg_directories).map { |f| "<key>#{f}</key><dict></dict>" }.join("")}
+            #{(pkg_files + pkg_directories).map { |f| "<key>#{f}</key><dict></dict>" }.join}
           </dict>
         </dict>
         </plist>
diff --git a/Library/Homebrew/test/cask/system_command_spec.rb b/Library/Homebrew/test/cask/system_command_spec.rb
index ba5ea03fcb..6e7397931f 100644
--- a/Library/Homebrew/test/cask/system_command_spec.rb
+++ b/Library/Homebrew/test/cask/system_command_spec.rb
@@ -66,10 +66,10 @@ describe Hbc::SystemCommand, :cask do
 
     describe "with default options" do
       it "echoes only STDERR" do
-        expected = [2, 4, 6].map { |i| "==> #{i}\n" }.join("")
+        expected = [2, 4, 6].map { |i| "#{i}\n" }.join
         expect {
           described_class.run(command, options)
-        }.to output(expected).to_stdout
+        }.to output(expected).to_stderr
       end
 
       include_examples("it returns '1 2 3 4 5 6'")
@@ -80,12 +80,10 @@ describe Hbc::SystemCommand, :cask do
         options.merge!(print_stdout: true)
       end
 
-      it "echoes both STDOUT and STDERR" do
-        (1..6).each do |i|
-          expect {
-            described_class.run(command, options)
-          }.to output(/==> #{ i }/).to_stdout
-        end
+      it "echoes both STDOUT and STDERR", :focus do
+        expect { described_class.run(command, options) }
+          .to output("1\n3\n5\n").to_stdout
+          .and output("2\n4\n6\n").to_stderr
       end
 
       include_examples("it returns '1 2 3 4 5 6'")
@@ -111,7 +109,7 @@ describe Hbc::SystemCommand, :cask do
       end
 
       it "echoes only STDOUT" do
-        expected = [1, 3, 5].map { |i| "==> #{i}\n" }.join("")
+        expected = [1, 3, 5].map { |i| "#{i}\n" }.join
         expect {
           described_class.run(command, options)
         }.to output(expected).to_stdout
diff --git a/Library/Homebrew/utils/tty.rb b/Library/Homebrew/utils/tty.rb
index 6e321b2f9b..eb6f02746f 100644
--- a/Library/Homebrew/utils/tty.rb
+++ b/Library/Homebrew/utils/tty.rb
@@ -6,10 +6,12 @@ module Tty
   end
 
   def width
-    width = `/bin/stty size 2>/dev/null`.split[1]
-    width = `/usr/bin/tput cols 2>/dev/null`.split[0] if width.to_i.zero?
-    width ||= 80
-    width.to_i
+    @width ||= begin
+      width = `/bin/stty size 2>/dev/null`.split[1]
+      width = `/usr/bin/tput cols 2>/dev/null`.split[0] if width.to_i.zero?
+      width ||= 80
+      width.to_i
+    end
   end
 
   def truncate(string)