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gawk: Include Files

 
 2.7 Including Other Files into Your Program
 ===========================================
 
 This minor node 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.  Note that source files may also be included using the '-i'
 option.
 
    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 script test1.
      -| This is script 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
      constant 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 script test1.
      -| This is script test2.
      -| This is script test3.
 
    The file name can, of course, be a pathname.  For example:
 
      @include "../io_funcs"
 
 and:
 
      @include "/usr/awklib/network"
 
 are both 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 (AWKPATH
 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," either by
 using 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 keep library files
 in more than one directory; 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.
 
    The rules for finding a source file described in AWKPATH
 Variable also apply to files loaded with '@include'.
 

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