无法重定向bas​​h中的stdin

Question

I am playing with file descriptors. A common practice is to redirect stdout and stderr using file descriptors, like this:

$ ls >files.txt 2>errors.txt

another example might be:

$ echo 'Hello there' > message.txt 2> errors.txt

however the following does not work:

$ echo 'Hello There' 0> input_message.txt > output_message.txt 2> errors.txt

It seems like the file descriptor 0 is not working as input_message.txt is empty, I'd expect to find the text message Hello There instead.

Why is that ?

Answer 1

You use < (or 0< ) to redirect stdin, like:

command <file

or:

command <&fd

where fd is a file descriptor opened for reading.

As for your example, since echo ignores stdin, this correction won't change the behavior.

See Bash Reference Manual § 3.6 Redirections .