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gawk: Rewind Function

 10.3.2 Rereading the Current File
 Another request for a new built-in function was for a function that
 would make it possible to reread the current file.  The requesting user
 didn't want to have to use 'getline' (⇒Getline) inside a loop.
    However, as long as you are not in the 'END' rule, it is quite easy
 to arrange to immediately close the current input file and then start
 over with it from the top.  For lack of a better name, we'll call the
 function 'rewind()':
      # rewind.awk --- rewind the current file and start over
      function rewind(    i)
          # shift remaining arguments up
          for (i = ARGC; i > ARGIND; i--)
              ARGV[i] = ARGV[i-1]
          # make sure gawk knows to keep going
          # make current file next to get done
          # do it
    The 'rewind()' function relies on the 'ARGIND' variable (⇒
 Auto-set), which is specific to 'gawk'.  It also relies on the
 'nextfile' keyword (⇒Nextfile Statement).  Because of this, you
 should not call it from an 'ENDFILE' rule.  (This isn't necessary
 anyway, because 'gawk' goes to the next file as soon as an 'ENDFILE'
 rule finishes!)
    You need to be careful calling 'rewind()'.  You can end up causing
 infinite recursion if you don't pay attention.  Here is an example use:
      $ cat data
      -| a
      -| b
      -| c
      -| d
      -| e
      $ cat test.awk
      -| FNR == 3 && ! rewound {
      -|    rewound = 1
      -|    rewind()
      -| }
      -| { print FILENAME, FNR, $0 }
      $ gawk -f rewind.awk -f test.awk data 
      -| data 1 a
      -| data 2 b
      -| data 1 a
      -| data 2 b
      -| data 3 c
      -| data 4 d
      -| data 5 e
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