output appended to that file. If the name begins with a number followed
by an equal sign ("="), then the number and the equal sign are stripped
off from the name, and the number is used to set the trace level. For

  DBI_TRACE=1=dbitrace.log perl

On Unix‐like systems using a Bourne‐like shell, you can do this easily
on the command line:

  DBI_TRACE=2 perl