2.1.2 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.(6)

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? Ctrl-d