>filein, 'filename'
 >list
 ; output from 'filename'
 >list
 ; here you see contents of 'filename'
 > load_new_sdfits_rows; even though 'filename' hasnt changed
 >'No sdfits file(s) in index need updating'
 ; now new rows are appended to 'filename' (by the online filler perhaps)
 > load_new_sdfits_rows
 >'Index file updated with 5 rows'
 >list
 ; here you see the original contents of 'filname'
 ; plus the extra 5 new rows.
 ; NOTE: the index file was NOT re-created from scatch