What does "cat -" do on the Unix command line?

Hello I would like to know the what exactly does cat - mean in Unix? I was recently reading through an article that mentioned this command and couldn't understand what it did.

Dave's Answer:

"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.

Categorized: Unix and Linux Help (Article 4137, Written by Dave Taylor)
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Comments

Note that "cat -" is basically "cat" anyway.

Posted by: monsieur at May 17, 2006 5:05 AM

hi
Please i will be very happy if you could please tell me what does Cat do in linux system

thanks

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