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gawk: Shell Quoting

 10.2.9 Quoting Strings to Pass to the Shell
 Michael Brennan offers the following programming pattern, which he uses
      #! /bin/sh
      INPUT_PROGRAM | awk "$awkp" | /bin/sh
    For example, a program of his named 'flac-edit' has this form:
      $ flac-edit -song="Whoope! That's Great" file.flac
    It generates the following output, which is to be piped to the shell
      chmod +w file.flac
      metaflac --remove-tag=TITLE file.flac
      LANG=en_US.88591 metaflac --set-tag=TITLE='Whoope! That'"'"'s Great' file.flac
      chmod -w file.flac
    Note the need for shell quoting.  The function 'shell_quote()' does
 it.  'SINGLE' is the one-character string '"'"' and 'QSINGLE' is the
 three-character string '"\"'\""':
      # shell_quote --- quote an argument for passing to the shell
      function shell_quote(s,             # parameter
          SINGLE, QSINGLE, i, X, n, ret)  # locals
          if (s == "")
              return "\"\""
          SINGLE = "\x27"  # single quote
          QSINGLE = "\"\x27\""
          n = split(s, X, SINGLE)
          ret = SINGLE X[1] SINGLE
          for (i = 2; i <= n; i++)
              ret = ret QSINGLE SINGLE X[i] SINGLE
          return ret
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