HEADFITS

       Read a FITS (primary or extension) header into a string array.

       HEADFITS() can also read gzip (.gz) or Unix compressed (.Z) FITS files.

       Result = HEADFITS(Filename/Fileunit ,[ ERRMSG =, EXTEN= , COMPRESS=,
                                            /SILENT ])

       Filename = String containing the name of the FITS file to be read.
                File names ending in '.gz' are assumed to be gzip'ed compressed
                and under Unix file names ending in '.Z' are assumed to be
                Unix compressed, and file names ending in .bz2 are assumed to
                be bzip2 compressed.    If this default behaviour is not
                sufficient then use the COMPRESS keyword.
                            or
       Fileunit - A scalar integer specifying the unit of an already opened
                  FITS file.  The unit will remain open after exiting
                  HEADFITS().  There are two possible reasons for choosing
                  to specify a unit number rather than a file name:
          (1) For a FITS file with many extensions, one can move to the
              desired extensions with FXPOSIT() and then use HEADFITS().  This
              is more efficient that repeatedly starting at the beginning of
              the file.
          (2) For reading a FITS file across a Web http: address after opening
              the unit with the SOCKET procedure (IDL V5.4 or later,
              Unix and Windows only)

      EXTEN  = integer scalar, specifying which FITS extension to read.
               For example, to read the header of the first extension set
               EXTEN = 1.   Default is to read the primary FITS header
               (EXTEN = 0).    The EXTEN keyword cannot be used when a unit
               number is supplied instead of a file name.
     COMPRESS - If this keyword is set and non-zero, then treat the file
              as compressed.  If 1 assume a gzipped file.   Use IDL's
              internal decompression facilities for gzip files, while for
              Unix or bzip2 compression spawn off a process to decompress and
              use its output as the FITS stream.  If the keyword is not 1,
              then use its value as a string giving the command needed for
              decompression.   See FXPOSIT for more info.
     /SILENT - If set, then suppress any warning messages about invalid
              characters in the FITS file.

       ERRMSG  = If this keyword is present, then any error messages will be
                 returned to the user in this parameter rather than
                 depending on the MESSAGE routine in IDL.  If no errors are
                 encountered, then a null string is returned.

       Result of function = FITS header, string array

       Print the main FITS header of a file 'test.fits' into a string
       variable, h
       IDL>  print, headfits( 'test.fits')
       Print the second extension header of a gzip compressed FITS file
       'test.fits.gz'.  Use HPRINT for pretty format
       IDL> hprint, headfits( 'test.fits.gz', ext=2)

       FXPOSIT(), MRD_HREAD

       adapted by Frank Varosi from READFITS by Jim Wofford, January, 24 1989
       Keyword EXTEN added, K.Venkatakrishna, May 1992
       Make sure first 8 characters are 'SIMPLE'  W. Landsman October 1993
       Check PCOUNT and GCOUNT   W. Landsman    December 1994
       Major rewrite, work for Unix gzip files,   W. Landsman  April 1996
       Converted to IDL V5.0   W. Landsman   September 1997
       Added COMPRESS keyword  W. Landsman   April 2000
       Added ERRMSG keyword    W. Landsman   July 2000
       Added /SILENT keyword   W. Landsman    December 2000
       Option to read a unit number rather than file name W.L    October 2001
       Test output status of MRD_HREAD call October 2003 W. Landsman

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