Logging

As any program (and REXX is no exception) lumbers along, it's often a good idea to keep track of what's happening, so that if something goes south later, you'll have some idea of where that happened.  A log-file is a good way to cover that.  Ideally, you want to have a separate file for each execution of the program so that if multiple users are banging away, each one has their activity logged to a unique spot.  That implies the log files will have different names, probably with a timestamp.  Here's the technique I use with great success:

   parse value Date("S")  Time("S")  Time("N")  with,
               yyyymmdd   sssss      hhmmss  .
   parse var yyyymmdd  4 yrdigit 5 mm 7 dd          /* 9 12 14 maybe */
   if Pos(yrdigit,"13579") > 0 then mm = mm + 12       /* mm=24      */
   logtag = Substr("ABCDEFGHIJKLMNOPQRSTUVWX",mm,1)    /* logtag=X   */
   subid  = logtag""dd""Right(sssss,5,0)               /* X1423722 ? */

The initial "parse" snags coherent date-and-time information.  Doing this on a single statement guarantees that the time will be proper for the date.  The second "parse" peels off the one-digit year ( '3' in 2013 ) so that we can determine whether it is odd ( if Pos(yrdigit,"13579") > 0 ).  If it is, we add 12 to the month value ( mm = mm + 12 ).  Next, we grab the mm^th value from the string of the first 24 letters of the alphabet.  We are now ready to form the unique part of the log file's dataset name:

   logdsn = "LOG."exec_name"."subid".LIST"

Put the exec's name as part of the log file's name.  If a routine calls a subroutine which also generates a log file, you don't want to cause a conflict.

Now all you have to do is allocate the dataset with a proper DCB and start filling it with progress notes.