ruby文件操作

1、文件的打开与关闭
    ``r'' Read-only, starts at beginning of file (default mode).
    ``r+'' Read-write, starts at beginning of file.
    ``w'' Write-only, truncates existing file to zero length or creates a new file for writing.
    ``w+'' Read-write, truncates existing file to zero length or creates a new file for reading and writing.
    ``a'' Write-only, starts at end of file if file exists, otherwise creates a new file for writing.
    ``a+'' Read-write, starts at end of file if file exists, otherwise creates a new file for reading and writing.
    ``b'' (DOS/Windows only) Binary file mode (may appear with any of the key letters listed above).
     使用file.new方法获取一个文件句柄来对文件操作，操作结束后file.close来关闭文件。
     file.open方法是new方法的扩充，该方法可有代码块，该代码块结束后自动close，而且在操作过程中发生错误时能够自动收集错误并推出
    如    
    file.open("filepath") do |file|
        file.each do |line| ... end
    end
    一些文件的常用命令：
    File.open(dir+"/read.txt","w") do |file|
    file.puts("djkjsadlkjdkdsfdsee")
end puts File.exists?(dir+"/read.txt")       文件是否存在
puts File.directory?(dir+"/read.txt")    文件是否是目录路径
puts File.file?(dir+"/read.txt")        是否是文件
puts File.zero?(dir+"/read.txt")        文件内容长度是否为0
puts File.size(dir+"/read.txt")        获取文件大小
put