LINUX: Send the last 3 lines of the output of the who command to a file called out1?

deathgripping · 12-01-2016, 02:37 PM

I recently learned about Filters in my Linux class. However this is throwing me off. I know what the who command is and about the tail command but how do I send it to a out1? And where does who fit into this?

is it

who tail +3 > out1 ?

Any help is appreciated.

suicidaleggroll · 12-01-2016, 03:05 PM

Close

As written, you're passing "tail" and "+3" as arguments to "who". What you need instead is to run "who" by itself, and redirect its output to the input of "tail". In Linux there are two types of I/O redirection, ">" and ">>" redirects output to a file, which you have done correctly, while "|" redirects output to the input of another process. You need to stick a "|" between "who" and "tail" so that the "tail" program can process the output of "who", rather than passing the literal string "tail" as an argument to "who".

Habitual · 12-01-2016, 03:06 PM

Code:

tail -3 who >> out1

spews error.
Did you notice?

Code:

who

and

Code:

who | tail -3

output are essentially equal result here, so unless the who utility is somehow 'different' on your system,

Code:

who >> out1

should do it.
Never ever saw

Code:

tail -3 who #whatever

before now.

See http://www.tldp.org/LDP/abs/html/io-redirection.html