The first command to know is cat;. To use it,
type cat, and then :
If you now have a cursor on a line by itself, you've done the correct thing. There are several variances you could have typed--some would work, some wouldn't.
Thus, the shell informs you that it couldn't find a program named ``ct'' and gives you another prompt to work with. Remember, Unix is case sensitive: CAT is a misspelling.
This produces the correct result and runs the cat program.
I assume you are now in cat;. Hopefully, you're wondering what it is doing. For all you hopefuls, no, it is not a game. cat is a useful utility that won't seem useful at first. Type anything, and hit return. What you should have seen is:
(The slanted text indicates what the user types.) What cat seems to do is echo the text right back at yourself. This is useful at times, but isn't right now. So let's get out of this program and move onto commands that have more obvious benefits.
To end many Unix commands, type
.
is the end-of-file character, or EOF for short.; Alternatively, it stands for end-of-text, depending on what book you
read. I'll refer to it as an end-of-file. It is a control character
that tells Unix programs that you (or another program) is done
entering data. When cat sees you aren't typing anything else,
it terminates.
For a similar idea, try the program sort.; As its
name indicates, it is a sorting program. If you type a couple of
lines, then press
, it will output those lines in a sorted order.
By the way, these types of programs are called
filtersfilter, because they take in text, filter it, and
output the text slightly differently. (Well, cat is a very basic
filter and doesn't change the input.) We will talk more about filters
later.