1.1.2 Running awk Without Input Files

You can also run awk without any input files. If you type the following command line:

awk 'program'

awk applies the program to the standard input, which usually means whatever you type on the keyboard. This continues until you indicate end-of-file by typing Ctrl-d. (On non-POSIX operating systems, the end-of-file character may be different.)

As an example, the following program prints a friendly piece of advice (from Douglas Adams’s The Hitchhiker’s Guide to the Galaxy), to keep you from worrying about the complexities of computer programming:

$ awk 'BEGIN { print "Don\47t Panic!" }'
-| Don't Panic!

awk executes statements associated with BEGIN before reading any input. If there are no other statements in your program, as is the case here, awk just stops, instead of trying to read input it doesn’t know how to process. The ‘\47’ is a magic way (explained later) of getting a single quote into the program, without having to engage in ugly shell quoting tricks.

NOTE: If you use Bash as your shell, you should execute the command ‘set +H’ before running this program interactively, to disable the C shell-style command history, which treats ‘!’ as a special character. We recommend putting this command into your personal startup file.

This next simple awk program emulates the cat utility; it copies whatever you type on the keyboard to its standard output (why this works is explained shortly):

$ awk '{ print }'
Now is the time for all good men
-| Now is the time for all good men
to come to the aid of their country.
-| to come to the aid of their country.
Four score and seven years ago, ...
-| Four score and seven years ago, ...
What, me worry?
-| What, me worry?
Ctrl-d