Why isn't `which ls | file` working?

Question

I would like to use the result of which ls and see the file type using file. However, when I type in which ls | file it doesn't work. When I try to do file < which ls, that doesn't work either.

Any pointers would be appreciated.

Use `type -a ls` instead. Which is not reliable to use for what you wanr — Valentin Bajrami, Dec 19 '22 at 07:24
@ValentinBajrami Thank you for trying to answer, but I was looking for the result of `file /usr/bin/ls`... Except, I would like to to check for `which` at the same time, and then use the result with `file`. — Grateful, Dec 19 '22 at 07:29
Does this answer your question? [whereis, pipline and ls](https://unix.stackexchange.com/questions/364079/whereis-pipline-and-ls) — muru, Dec 19 '22 at 07:43

score 2 · Accepted Answer · edited Dec 19 '22 at 07:39

2

This does not work because file takes the file to examine as commandline parameter (see man file).

You are piping the output of which to the stdin of the process executing ls.

What you should do is something like file "$(which ls)".

edited Dec 19 '22 at 07:39

Stephen Kitt

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answered Dec 19 '22 at 07:26

gerhard d.

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Aaaah... Perfect! – Grateful Dec 19 '22 at 07:31
But then, why is it that I am able to do something like `man ls | head`... Although, `head` would also be expecting command line arguments ? – Grateful Dec 19 '22 at 07:40
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From `man head`: `With no FILE, or when FILE is -, read standard input.`. This means, that `head` takes *stdin* if no FILE is given. – gerhard d. Dec 19 '22 at 07:55
Aaaah! That makes sense, thank you so much!! – Grateful Dec 19 '22 at 08:17

Why isn't `which ls | file` working?

1 Answers1