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(gawk.info)Getline/Variable/File

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Enter node , (file) or (file)node

Using `getline' into a Variable from a File
-------------------------------------------

   Use `getline VAR < FILE' to read input from the file FILE, and put
it in the variable VAR.  As above, FILE is a string-valued expression
that specifies the file from which to read.

   In this version of `getline', none of the built-in variables are
changed and the record is not split into fields.  The only variable
changed is VAR.  For example, the following program copies all the
input files to the output, except for records that say
`@include FILENAME'.  Such a record is replaced by the contents of the
file FILENAME:

     {
          if (NF == 2 && $1 == "@include") {
               while ((getline line < $2) > 0)
                    print line
               close($2)
          } else
               print
     }

   Note here how the name of the extra input file is not built into the
program; it is taken directly from the data, from the second field on
the `@include' line.

   The `close' function is called to ensure that if two identical
`@include' lines appear in the input, the entire specified file is
included twice.  Note: Closing Input and Output Redirections.


   One deficiency of this program is that it does not process nested
`@include' statements (i.e., `@include' statements in included files)
the way a true macro preprocessor would.  Note: An Easy Way to Use
Library Functions, for a program that does handle nested
`@include' statements.