12.2. What Good Is a cat?
may well be the first command new users hear about, if only because
of its odd name. cat stands for
concatenate or, as some
would say, catenate. Both words mean the same thing: to connect in a
series. The cat command takes its filename
arguments and strings their contents together. Essentially,
cat takes its input and spits it out again.
cat has many uses, but the four most basic
applications are described in the following list. In many ways, they
don't illustrate cat so much as
they illustrate the shell's output redirection (Section 43.1) mechanism.
% cat file
% cat file1 file2 file...
Use this form to display one or more files on the screen. The output
doesn't pause when the screen is full. As a result,
if your files are more than one screenful long, the output will whiz
by without giving you a chance to read it. To read output by
screenfuls, use a pager such as less
% cat file(s) > new_file
Use this form when you want to combine several smaller files into one
large file. Be sure the destination file does not already exist;
otherwise, it will be replaced by the new contents (effectively
destroying the original). For example, the command:
% cat chap1 chap2 chap3 > book
creates a new file, book, composed of three
files, one after the other. The three component files still exist as
chap1, chap2, and
% cat file >> existing_file
% cat files >> existing_file
Use this form to add one or more files to the end of an existing
file. For example:
% cat note1 note2 > note_list
% cat note3 >> note_list
% cat > newfile
Use this form as a quick-and-dirty way to create a new file. This is
useful when you aren't yet familiar with any of the
standard text editors. With this command, everything you type at the
keyboard goes into the new file. (You won't be able
to back up to a previous line.) To finish your input, enter CTRL-d on
a line by itself.
Well, that was just in case there are some beginners on board.
Section 12.4, Section 12.7,
and Section 12.13 give some more useful tips about
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