Cat is a fairly simple tool designed to concatenate and write file(s) to your screen, which is known as standard output (stdout). It is part of the GNU Core Utils released under the GPLv3+ license. You can expect to find it in just about any Linux distribution or other Unix operating environment, such as FreeBSD or Solaris. The simplest use of cat is to show the contents of a file. Here is an example with a file named hello.world:
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