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 terminal. This continues until you indicate end-of-file by typing Ctrl-d. (On other operating systems, the end-of-file character may be different. For example, on OS/2 and MS-DOS, it is Ctrl-z.)

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 (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.¹

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