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  link RINEX files from a specified directory to the current day directory
  
  USAGE :    sh_link_rinex  -year <yr> -days <doy> -ndays <-n +n> -sesfo <shr smin dhr dmin> -dir <dir> -minspan <hrs> 
  
          <yr> is the 4 char year of observations. [Required]
  
          <doy> is the 3 char day of the year to be linked. [Required]
                Note: multiple days may be entered to be linked
  
          <ndays> are the number of days before and after the first doy entered to be linked
                  Note: +n -n values are relative to the first doy value entered 
  
          <sesfo> shr and smin: start of obs to link, dhr and dmin: duration of obs to link
                  Note: sesfo values are relative to the first doy value entered 
  
          <dir> the absolute or relative path to the rinex files [Default ../rinex] 
                Note: multiple directories may be entered and searched
  
          <hrs> the minimum interval of data that will be accepted in any session. [Default 1 hr]  
  
  Example :   sh_link_rinex -year 1996 -days 016 017 -dir ../rinex/tracking 
              sh_link_rinex -year 1996 -days 016 -ndays 3 3 -dir ../rinex/tracking 
              sh_link_rinex -year 1996 -days 016 -ndays 3 3 -sesfo 17 00 24 00 -dir ../rinex/tracking 
  
 IMPORTANT: -year and -days must be the first 2 command line arguments. 
 
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