有没有办法在 Rails 控制台内的输出上实现类似 grep 的功能

Question

在 shell 中，我可以在 Rails Console 内执行

$ cat name_of_file_with_a_lot_of_text | grep "What I am looking for"

，我可以实现类似的功能吗，比如当我运行命令并且输出很大时，尤其是数据库查询。

我知道将其输出为 YAML，但这不是我想要的。

谢谢。

Answer 1

是的，你可以。该方法称为gr...wait it...ep。 Ruby 的 grep 适用于 String、Array 和许多其他内置对象。例如，要获取某个数字的所有 to_xxx 方法，只需执行以下操作：

 1.methods.grep(/to_/)

Answer 2

我也有同样的问题，并且对 ream88 的有点尖刻的回答不太满意，所以我决定尝试一下。

# Allows you to filter output to the console using grep
# Ex:
#   def foo
#     puts "Some debugging output here"
#     puts "The value of x is y"
#     puts "The value of foo is bar"
#   end
# 
#   grep_stdout(/value/) { foo }
#   # => The value of x is y
#   # => The value of foo is bar
#   # => nil
def grep_stdout(expression)
  # First we need to create a ruby "pipe" which is two sets of IO subclasses
  # the first is read only (which represents a fake $stdin) and the second is
  # write only (which represents a fake $stdout).
  placeholder_in, placeholder_out = IO.pipe

  # This child process handles the grep'ing.  Its done in a child process so that
  # it can operate in parallel with the main process.
  pid = fork {
    # sync $stdout so we can report any matches asap
    $stdout.sync

    # replace $stdout with placeholder_out
    $stdin.reopen(placeholder_in)

    # we have to close both placeholder_out and placeholder_in because all instances
    # of an IO stream must be closed in order for it to ever reach EOF.  There's two
    # in this method; one in the child process and one in the main process.
    placeholder_in.close
    placeholder_out.close

    # loop continuously until we reach EOF (which happens when all
    # instances of placeholder_out have closed)
    read_buffer = ''
    loop do
      begin
        read_buffer << $stdin.readpartial(4096)
        if line_match = read_buffer.match(/(.*\n)(.*)/)
          print line_match[1].grep(expression)  # grep complete lines
          read_buffer = line_match[2]           # save remaining partial line for the next iteration
        end
      rescue EOFError
        print read_buffer.grep(expression)  # grep any remaining partial line at EOF
        break
      end
    end
  }

  # Save the original stdout out to a variable so we can use it again after this
  # method is done
  original_stdout = $stdout

  # Redirect stdout to our pipe
  $stdout = placeholder_out

  # sync $stdout so that we can start operating on it as soon as possible
  $stdout.sync

  # allow the block to execute and save its return value
  return_value = yield

  # Set stdout back to the original so output will flow again
  $stdout = original_stdout

  # close the main instances of placeholder_in and placeholder_out
  placeholder_in.close
  placeholder_out.close

  # Wait for the child processes to finish
  Process.wait pid

  # Because the connection to the database has a tendency to go away when calling this, reconnect here
  # if we're using ActiveRecord
  if defined?(ActiveRecord)
    suppress_stdout { ActiveRecord::Base.verify_active_connections! }
  end

  # return the value of the block
  return_value
end

我的解决方案的明显缺点是输出丢失。我不知道如何在不调用 yield 两次的情况下解决这个问题。

编辑我已将答案更改为仅调用fork一次，这使我可以保留块的输出并在最后返回它。赢。

编辑2您现在可以在这个gem中获得所有这些功能（以及更多！）https: //github.com/FutureAdvisor/console_util