cat(1) is short for “concatenate”. It
was originally designed to merge text files into one, but can be used for
many other purposes.
To merge two or more files into one, you simply list the files after the
cat command and then redirect the new output to a file.
cat works with standard input and standard output, so
you have to use the shell redirection characters. For example:
$ cat file1 file2 file3 > bigfile
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This command takes the contents of file1,
file2, and file3 and merges it
all together. The new output is sent to standard out.
One can also use cat to display files. Many people
“cat” text files through the more or
less commands, like this:
That will display the file1 file and pipe it through
the more command so that you only get one screen
at a time.
Another common use for cat is copying files. You can
copy any file around with cat, like this:
$ cat /bin/bash > ~/mybash
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The /bin/bash program is copied to your home
directory and named “mybash”.
cat has many uses and the ones discussed here are just a
few. Since cat makes extensive use of standard input
and standard output, it is ideal for use in shell scripts or part of other
complex commands.