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I am a very beginner of unix, and working on putty shell environment.

I know standard input, output, and error are streams and related to file descriptors, but I did not understand clearly what /dev/stdin does.

  1. What is '/dev/stdin/ and how to use?

  2. Is it a special (block or character) file of a device?

Godpoong
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  • What have you done for this question? – 炸鱼薯条德里克 Apr 21 '19 at 01:32
  • I did $ echo hello | cp /dev/stdin /dev/stdout and $ cat /dev/stdin >resultfile to figure out what is the role of /dev/stdin – Godpoong Apr 21 '19 at 02:39
  • For the 2nd question, do file /dev/stdin. Your path is wrong, the trailing slash is redundant. – Weijun Zhou Apr 21 '19 at 04:30
  • If you want to copy the content of /dev/stdin to /dev/stdout, you should use dd if=/dev/stdin of=/dev/stdout, cp copies the special file itself, it requires superuser privilege to do this cp. After all, it does not make sense to copy the file itself and you should not try sudo cp /dev/stdin /dev/stdout. Please also check man dup2. – Weijun Zhou Apr 21 '19 at 04:39
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    @WeijunZhou cp /dev/stdin /dev/stdout works fine. example: echo yup | cp /dev/stdin /dev/stdout. And this works with both BSD's dup-like /dev/std{in,out} and with Linux's fake symlinks and quirks. Where did you get that superuser privilege idea from? –  Apr 21 '19 at 16:26
  • I get the idea from the permission of /dev/, but now I realize it's wrong. Also I have an aliased cp when I did the tests. – Weijun Zhou Apr 21 '19 at 16:37

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