From another forum I have learned that perldb requires STDOUT to be a terminal, so that the ">../to_excel/excnnnnn.txt" in my invocation line caused my problem. This would not have to be the case: the writer on the site where I learned about this feature noted that perldb could find the terminal from any of STDIN, STDOUT, or STDERR, whichever was not redirected.

SUGGESTION FOR FUTURE WORK ON perldb!!

As it is, I will revise the program to open and use the output file named in ARGV[0], and leave my command line unchanged except for replacing '>' with a space.