2.7 Including Other Files Into Your Program

This section describes a feature that is specific to gawk.

The ‘@include’ keyword can be used to read external awk source files. This gives you the ability to split large awk source files into smaller, more manageable pieces, and also lets you reuse common awk code from various awk scripts. In other words, you can group together awk functions, used to carry out specific tasks, into external files. These files can be used just like function libraries, using the ‘@include’ keyword in conjunction with the AWKPATH environment variable.

Let’s see an example. We’ll start with two (trivial) awk scripts, namely ‘test1’ and ‘test2’. Here is the ‘test1’ script:

BEGIN {
    print "This is script test1."
}

and here is ‘test2’:

@include "test1"
BEGIN {
    print "This is script test2."
}

Running gawk with ‘test2’ produces the following result:

$ gawk -f test2
-| This is file test1.
-| This is file test2.

gawk runs the ‘test2’ script which includes ‘test1’ using the ‘@include’ keyword. So, to include external awk source files you just use ‘@include’ followed by the name of the file to be included, enclosed in double quotes.

NOTE: Keep in mind that this is a language construct and the file name cannot be a string variable, but rather just a literal string in double quotes.

The files to be included may be nested; e.g., given a third script, namely ‘test3’:

@include "test2"
BEGIN {
    print "This is script test3."
}

Running gawk with the ‘test3’ script produces the following results:

$ gawk -f test3
-| This is file test1.
-| This is file test2.
-| This is file test3.

The file name can, of course, be a pathname. For example:

@include "../io_funcs"

or:

@include "/usr/awklib/network"

are valid. The AWKPATH environment variable can be of great value when using ‘@include’. The same rules for the use of the AWKPATH variable in command-line file searches (see section The AWKPATH Environment Variable) apply to ‘@include’ also.

This is very helpful in constructing gawk function libraries. If you have a large script with useful, general purpose awk functions, you can break it down into library files and put those files in a special directory. You can then include those “libraries,” using either the full pathnames of the files, or by setting the AWKPATH environment variable accordingly and then using ‘@include’ with just the file part of the full pathname. Of course you can have more than one directory to keep library files; the more complex the working environment is, the more directories you may need to organize the files to be included.

Given the ability to specify multiple ‘-f’ options, the ‘@include’ mechanism is not strictly necessary. However, the ‘@include’ keyword can help you in constructing self-contained gawk programs, thus reducing the need for writing complex and tedious command lines. In particular, ‘@include’ is very useful for writing CGI scripts to be run from web pages.

As mentioned in The AWKPATH Environment Variable, the current directory is always searched first for source files, before searching in AWKPATH, and this also applies to files named with ‘@include’.