Take notes on the command line is part of Short Circuit's Console Program Basics selection.
Invoking NOTES without commandline arguments displays the current contents of the local NOTES.TXT if it exists.
If NOTES has arguments, the current date and time are appended to the local NOTES.TXT followed by a newline.
Then all the arguments, joined with spaces, prepended with a tab, and appended with a trailing newline, are written to NOTES.TXT.
If NOTES.TXT doesn't already exist in the current directory then a new NOTES.TXT file should be created.

/*REXX program  implements the  "NOTES"  command  (append text to a file from the C.L.).*/
timestamp=right(date(),11,0)  time()  date('W')  /*create a (current) date & time stamp.*/
nFID = 'NOTES.TXT'                               /*the  fileID  of the  "notes"  file.  */
 
if 'f2'x==2  then tab="05"x                      /*this is an EBCDIC system.            */
             else tab="09"x                      /*  "   "  "  ASCII    "               */
 
if arg()==0  then do  while lines(nFID)          /*No arguments?  Then display the file.*/
                  say linein(Nfid)               /*display  a  line of file ──► screen. */
                  end   /*while*/
             else do
                  call lineout nFID,timestamp    /*append the timestamp to "notes" file.*/
                  call lineout nFID,tab||arg(1)  /*   "    "     text    "    "      "  */
                  end
                                                 /*stick a fork in it,  we're all done. */