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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.



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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

Posted by: John at January 10, 2008 12:16 AM

I have a lot to say, but ...
Starbucks coffee cup I have a lot to say, and questions of my own for that matter, but most of all I'd like to say thank you for all your efforts on this Web site by buying you a chai!

I do have a comment, now that you mention it!









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