如何在Mac OS X上模拟'cp --update'行为？

Question

的GNU/Linux version of cp有一个很好的--update标志：

-u，--update只 拷贝当源文件比目标文件或当目标文件丢失

新Mac OS X version of cp缺少这个标志。

通过使用内置系统命令行程序来获取cp --update行为的最佳方法是什么？我想避免安装任何额外的工具（包括GNU版本cp）。

Answer 1

rsync有一个-u/--update选项，作品就像GNU cp：

$ rsync -u src dest 

Answer 2

而且看的rsync的其他选项，这可能是你真正想要的东西：

-l, --links     copy symlinks as symlinks 
    -H, --hard-links   preserve hard links 
    -p, --perms     preserve permissions 
     --executability   preserve executability 
    -o, --owner     preserve owner (super-user only) 
    -g, --group     preserve group 
     --devices    preserve device files (super-user only) 
     --specials    preserve special files 
    -D       same as --devices --specials 
    -t, --times     preserve times 

    -a, --archive 
      This is equivalent to -rlptgoD. It is a quick way of saying you want recursion 
      and want to preserve almost everything (with -H being a notable omission). The 
      only exception to the above equivalence is when --files-from is specified, in which 
      case -r is not implied. 

      Note that -a does not preserve hardlinks, because finding multiply-linked files is 
      expensive. You must separately specify -H.