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gawk: Extension Exercises

 16.10 Exercises
   1. Add functions to implement system calls such as 'chown()',
      'chmod()', and 'umask()' to the file operations extension presented
      in ⇒Internal File Ops.
   2. Write an input parser that prints a prompt if the input is a from a
      "terminal" device.  You can use the 'isatty()' function to tell if
      the input file is a terminal.  (Hint: this function is usually
      expensive to call; try to call it just once.)  The content of the
      prompt should come from a variable settable by 'awk'-level code.
      You can write the prompt to standard error.  However, for best
      results, open a new file descriptor (or file pointer) on '/dev/tty'
      and print the prompt there, in case standard error has been
      Why is standard error a better choice than standard output for
      writing the prompt?  Which reading mechanism should you replace,
      the one to get a record, or the one to read raw bytes?
   3. (Hard.)  How would you provide namespaces in 'gawk', so that the
      names of functions in different extensions don't conflict with each
      other?  If you come up with a really good scheme, contact the
      'gawk' maintainer to tell him about it.
   4. Write a wrapper script that provides an interface similar to 'sed
      -i' for the "inplace" extension presented in ⇒Extension Sample
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