1 files changed, 88 insertions, 0 deletions
diff --git a/lib/rubygems/commands/which_command.rb b/lib/rubygems/commands/which_command.rb
new file mode 100644
index 0000000000..5ed4d9d142
--- /dev/null
+++ b/lib/rubygems/commands/which_command.rb
@@ -0,0 +1,88 @@
+# frozen_string_literal: true
+
+require_relative "../command"
+
+class Gem::Commands::WhichCommand < Gem::Command
+  def initialize
+    super "which", "Find the location of a library file you can require",
+          search_gems_first: false, show_all: false
+
+    add_option "-a", "--[no-]all", "show all matching files" do |show_all, options|
+      options[:show_all] = show_all
+    end
+
+    add_option "-g", "--[no-]gems-first",
+               "search gems before non-gems" do |gems_first, options|
+      options[:search_gems_first] = gems_first
+    end
+  end
+
+  def arguments # :nodoc:
+    "FILE          name of file to find"
+  end
+
+  def defaults_str # :nodoc:
+    "--no-gems-first --no-all"
+  end
+
+  def description # :nodoc:
+    <<-EOF
+The which command is like the shell which command and shows you where
+the file you wish to require lives.
+
+You can use the which command to help determine why you are requiring a
+version you did not expect or to look at the content of a file you are
+requiring to see why it does not behave as you expect.
+    EOF
+  end
+
+  def execute
+    found = true
+
+    options[:args].each do |arg|
+      arg = arg.sub(/#{Regexp.union(*Gem.suffixes)}$/, "")
+      dirs = $LOAD_PATH
+
+      spec = Gem::Specification.find_by_path arg
+
+      if spec
+        if options[:search_gems_first]
+          dirs = spec.full_require_paths + $LOAD_PATH
+        else
+          dirs = $LOAD_PATH + spec.full_require_paths
+        end
+      end
+
+      paths = find_paths arg, dirs
+
+      if paths.empty?
+        alert_error "Can't find Ruby library file or shared library #{arg}"
+        found = false
+      else
+        say paths
+      end
+    end
+
+    terminate_interaction 1 unless found
+  end
+
+  def find_paths(package_name, dirs)
+    result = []
+
+    dirs.each do |dir|
+      Gem.suffixes.each do |ext|
+        full_path = File.join dir, "#{package_name}#{ext}"
+        if File.exist?(full_path) && !File.directory?(full_path)
+          result << full_path
+          return result unless options[:show_all]
+        end
+      end
+    end
+
+    result
+  end
+
+  def usage # :nodoc:
+    "#{program_name} FILE [FILE ...]"
+  end
+end