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Creating a multi-record GRIB file

Mark Piper

I'm a little embarrassed about this, but last week I learned (or maybe "recalled" is more accurate) that you can create multi-record GRIB files using only the UNIX cat command. For example, with files a.grb and b.grb, I can make a new file c.grb with:

$ cat a.grb b.grb > c.grb
      

To perform the equivalent action solely within IDL, read the files as a bytestream, concatenate the data, then write the data back as a bytestream; e.g.:

IDL> a = read_binary('a.grb')
IDL> b = read_binary('b.grb')
IDL> c = [a, b]

IDL> openw, u, 'c.grb', /get_lun
IDL> writeu, u, c
IDL> free_lun, u
      

That's it. What do you think?

Note:

Actually, while writing this, I thought of a pair of feature requests.

  1. To complement the other FILE_* routines (FILE_MOVE, FILE_COPY, etc.), should IDL have a FILE_CAT routine? This would allow Windows users to have a UNIX "cat" equivalent in IDL.
  2. As a complement to READ_BINARY, should we have a WRITE_BINARY? It would bring the three lines of code used above down to one.

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