Name

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    MRD_HREAD

Purpose

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    Reads a FITS header from an opened disk file or Unix pipe

Explanation

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    Like FXHREAD but also works with compressed Unix files

Calling Sequence

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    MRD_HREAD, UNIT, HEADER [, STATUS, /SILENT, ERRMSG =, /FIRSTBLOCK ]

Inputs

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    UNIT = Logical unit number of an open FITS file

Outputs

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    HEADER = String array containing the FITS header.
  OPT. OUTPUTS:
    STATUS = Condition code giving the status of the read. Normally, this
                is zero, but is set to -1 if an error occurs, or if the
                first byte of the header is zero (ASCII null).

Optional Keyword Input

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      /FIRSTBLOCK - If set, then only the first block (36 lines or less) of
                the FITS header are read into the output variable. If only
                size information (e.g. BITPIX, NAXIS) is needed from the
                header, then the use of this keyword can save time. The
                file pointer is still positioned at the end of the header,
                even if the /FIRSTBLOCK keyword is supplied.
      /SILENT - If set, then warning messages about any invalid characters in
                the header are suppressed.
      /SKIPDATA - If set, then the file point is positioned at the end of the
                HDU after the header is read, i.e. the following data block
                is skipped. Useful, when one wants to the read the headers
                of multiple extensions.
      /NO_BADHEADER - if set, returns if FITS header has illegal characters
                By default, MRD_HREAD replaces bad characters with blanks,
                issues a warning, and continues.

Optional Output Parameter

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      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.

Restrictions

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      The file must already be positioned at the start of the header. It
      must be a proper FITS file.

Side Effects

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      The file ends by being positioned at the end of the FITS header, unless
      an error occurs.

Revision History

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      Written, Thomas McGlynn August 1995
      Modified, Thomas McGlynn January 1996
        Changed MRD_HREAD to handle Headers which have null characters
          A warning message is printed out but the program continues.
          Previously MRD_HREAD would fail if the null characters were
          not in the last 2880 byte block of the header. Note that
          such characters are illegal in the header but frequently
          are produced by poor FITS writers.
      Added /SILENT keyword W. Landsman December 2000
      Added /FIRSTBLOCK keyword W. Landsman February 2003
      Added ERRMSG, SKIPDATA keyword W. Landsman April 2009
      Close file unit even after error message W.L. October 2010
      Added /NO_BADHEADER Zarro (ADNET), January 2012