File.open('file.rb', 'r') do |f|
  while line = f.gets # f.getc 获取一个字符
    puts line
  end
end

File.open('test.rb','r') do |f|
  lines = f.readlines
end

File.readlines('file_util.rb') # 读取所有行
File.read('file_util.rb')  # 读取所有内容

File.open('test','w') do |f|
  f << 'hello'  # 追加
  f << 'world'
  f.puts 'hello'
  f.puts 'world'
end

irb(main):053:0> full_name="/mnt/d/code/ruby/r1.rb"
=> "/mnt/d/code/ruby/r1.rb"
irb(main):054:0> File.basename(full_name) # 文件名
=> "r1.rb"
irb(main):055:0> File.basename(full_name,'.rb')  # 去年后缀的文件名
=> "r1"
irb(main):056:0> File.dirname(full_name)  # 文件夹路径
=> "/mnt/d/code/ruby"
irb(main):057:0> File.extname(full_name)  # 后缀名
=> ".rb"
irb(main):058:0> File.join('/mnt/d','code')  # 拼接
=> "/mnt/d/code"
irb(main):059:0> File.expand_path("~/ruyb")  # 
=> "/home/andy/ruyb"
irb(main):064:0> File.exist?('.zshrc') # 是否存在
=> true
irb(main):066:0> File.directory?('/home/andy')  # 是否是文件夹
=> true
irb(main):067:0> File.file?('.bashrc')  # 是否文件
=> true
irb(main):068:0> File.size('.bashrc')  # 文件大小
=> 3772
File.rename('oldname','newname')  # 重命名
File.delete('test.rb')  # 删除
File.symlink('test','old_test')