"cat" is the 'concatenate' program and its purpose is to display the contents of one or more file. Add the '-' flag, however, and you have it display the content of "standard input" or "stdin": in a pipe like:
tail myfile | cat -
It's basically a null operation, since this is no different than doing:
tail myfile
A lot of shell script authors use structures like this too:
cat - << EOF
for what we script programmers call a
here document, but most times this can be accomplished in other ways that are more resource efficient on the system.
In general, the cat - command is sometimes useful for shell scripting, but in general usage you'll rarely, if ever, see it on a command line.
More Useful Unix and Linux Help Articles:
Sign up for my weekly AskDaveTaylor Newsletter and you'll receive even more tech and gadget help
right to your inbox, along with exclusive news and industry updates. It's good stuff. I promise!
Note that "cat -" is basically "cat" anyway.