awk without Input Files
You can also run awk without any input files. If you type the
command line:
awk 'program'
then awk applies the program to the standard input,
which usually means whatever you type on the terminal. This continues
until you indicate end-of-file by typing Control-d.
(On other operating systems, the end-of-file character may be different.
For example, on OS/2 and MS-DOS, it is Control-z.)
For example, the following program prints a friendly piece of advice (from Douglas Adams' The Hitchhiker's Guide to the Galaxy), to keep you from worrying about the complexities of computer programming (`BEGIN' is a feature we haven't discussed yet).
$ awk "BEGIN { print \"Don't Panic!\" }"
-| Don't Panic!
This program does not read any input. The `\' before each of the inner double quotes is necessary because of the shell's quoting rules, in particular because it mixes both single quotes and double quotes.
This next simple awk program
emulates the cat utility; it copies whatever you type at 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?
Control-d
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