Identifier   get_hdrkey

 Purpose      Read a keyword value and optionally the corresponding comment
              from the header of an ISAP structure

 Synopsis     status = get_hdrkey( header, keyword, value [,key_pos=key_pos]
                                   [,comment=comment][,stat=stat])

 Arguments    Name      I/O Type    Description
              -----------------------------------------------------
              header     I  string  The input header 
              keyword    I  string  Keyword to read from header
              value      O  varies  The value of the keyword. The type of the 
                                    output is determined by the type of the
                                    keyword: integers are returned as long, 
                                    logicals (T or F) are returned as byte 
                                    integers, i.e. 1B (true) or 0B (false).
                                    Floats and doubles are returned as double.
                                    Strings keep their type.
              key_pos    O  intarr(3) key_pos(0)=position of keyword in header
                                    string, key_pos(1) = posiion of '=',
                                    key_pos(2) = position of '/'
              comment    O  string  The comment for the keyword
              stat      I/O int     error status, 0 if ok, 1 if fatal

 Returns      return status code (0=success, 1=keyword not found)

 Description  Read a keyword from a header

 Comment      If the value is a string (indicated via quotation marks at the 
              beginning and end) then this routine assumes that the string 
              itself does not contain further quotation marks.

 Example      1) status = get_hdrkey( aar.header, 'object', value, key_pos)
              Gets the object name from the header

              2) comment= ''
                 status = get_hdrkey( aar.header, 'DATE', value, $
                          comment=comment)
              Gets the date and the corresponding comment from the header

 Dependencies   CALLS: sap_error
                CALLED FROM: disp_aar, get_unit, spect_form, wave_form,
                             wav_dop

 Category     ISAP

 Filename     get_hdrkey.pro 

 Author       E. Sturm  (--> ES)

 Version      1.1

 History      1.0   24-01-96  ES  First version
              1.1   09-07-96  ES  stat added

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Copyright (C) 1995, Max-Planck-Institut fuer extraterrestrische Physik (MPE);
                    Garching, Germany                                       ;
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