History Item

Most data sets will have an associated history item. This is a text file containing a description of the data set, and the processing that has been performed on it. The routines to access the history item are as follows:

      subroutine hisopen(tno,status)
      subroutine hisread(tno,line,eof)
      subroutine hiswrite(tno,line)
      subroutine hisinput(tno,taskname)
      subroutine hisclose(tno)

Hisopen must be called before the history item can be accessed. Here tno is the handle passed back by a previous call to xyopen or uvopen, and status is a string which can be either 'read', 'write' or 'append'. Hisread and hiswrite can be called to read from, or append to the history item a line at a time (line is a character string). When reading, the logical value eof turns true when the end of the history item is encountered. Hisinput writes a number of history comments, giving the command line input parameters. This is a particularly useful routine to summarize user inputs. For hisinput, taskname is the name of the task. Hisclose closes the history item.

Note that there is no routine to copy a history file from one dataset to another. This is easily performed using the hdcopy routine described in the previous section.

For uniformities sake, history comments follow a standard format. The following is an example of the history comments written by the task DEMOS:

DEMOS: Miriad DeMos: version 1.0 30-apr-90'
DEMOS: Input parameters are
DEMOS:   vis=uvn
DEMOS:   map=mosclean
DEMOS: Pointing offset used (arcsec):   24.0 -30.0

Note that all comments start with the task name. The first comment gives a version date of the program. The next three lines were generated by HisInput, and the last line was an extra comment.