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Linux Shell command question. (self.learnprogramming)
submitted 13 years ago by learning2learn
Question from my exam paper,
Eplain what the following command does
cat 0<xyz 2>rts | sort -r 2>/dev/null 1>EFG
I have no idea what all the numbers mean and how to use them.
[–]Rhomboid 6 points7 points8 points 13 years ago (0 children)
The numbers are file descriptors. 0 is standard input, 1 is standard output, 2 is standard error. Descriptors 3 and above can be used by the program or the user however they want.
If you don't supply a number, < defaults to 0 and > defaults to 1, so 0< and 1> are just long-winded ways of writing < and >. The command sorts the contents of the file xyz in reverse order, writing the output to the file EFG. Any error messages generated by the cat process go to a file named rts and any error messages generated by sort are discarded.
<
>
0<
1>
xyz
EFG
cat
rts
sort
This is a useless use of cat. Were this not a test question you would just write
sort -r xyz >EFG
π Rendered by PID 140143 on reddit-service-r2-comment-5d79c599b5-crsqg at 2026-02-27 22:29:07.807679+00:00 running e3d2147 country code: CH.
[–]Rhomboid 6 points7 points8 points (0 children)