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 -30.0Note 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.