Sometimes your awk programs can be very long. In this case, it is more convenient to put the program into a separate file. In order to tell awk to use that file for its program, you type:
awk -f source-file input-file1 input-file2 ...
The -f instructs the awk utility to get the awk program from the file source-file. Any file name can be used for source-file. For example, you could put the program:
BEGIN { print "Don't Panic!" }
into the file advice. Then this command:
awk -f advice
does the same thing as this one:
awk "BEGIN { print \"Don't Panic!\" }"
This was explained earlier (see Read Terminal). Note that you don't usually need single quotes around the file name that you specify with -f, because most file names don't contain any of the shell's special characters. Notice that in advice, the awk program did not have single quotes around it. The quotes are only needed for programs that are provided on the awk command line.
If you want to identify your awk program files clearly as such, you can add the extension .awk to the file name. This doesn't affect the execution of the awk program but it does make “housekeeping” easier.