Traps for Perl4 Programmers Migrating to Perl5
The introduction of all the new features and power in Perl5 has yielded some incompatibilities between Perl4 and Perl5. Most well-written Perl4 programs do run under Perl5 and produce the same results as they did under Perl4. A number of specific examples of Perl4 code, however, may not do what you expect them to do when you run them under Perl5. See PERLTRAP for a description of many of these examples. The latest version of PERLTRAP, as of the release of this book, is also included in Appendix A.
In general, you need to inspect your older Perl4 programs against the examples in PERLTRAP to be sure that they don't include any of the items that may produce unexpected results. If they fail to compile, you're in good shape, but watch out for traps that do compile. Also, using the -w switch to Perl is always advisable when you're running any script.