2.1 Versions

2.1 Versions

It's important to know as soon as possible what version of Perl the program was developed for. This isn't necessarily the same as the version of Perl it may currently be running against, but find that out anyway so you have an upper bound. Again, get this information from the gold source: the original running environment. Type the complete path to perl that appears in the main program's shebang line (see below) followed by the -v argument to find out the version; for example:

% /opt/bin/perl -v

This is perl, v5.6.1 built for i386-linux

Copyright 1987-2003, Larry Wall

If this output indicates that they're running on a newer perl than the one you have (run the same command on your perl), do whatever you can to upgrade. Although upgrading may be unnecessary, if you have any difficulties getting the code to work, your energy for debugging will be sapped by the nagging fear that the problem is due to a version incompatibility.

One reason upgrading may be unnecessary is that the operating group upgraded their perl after the original program was written, and the program did not trigger any of the forward incompatibilities. A program written for Perl 4 could easily work identically under Perl 5.8.3 and probably would; the Perl developers went to fanatical lengths to preserve backward compatibility across upgrades.

Look at the dates of last modifications of the source files. You may need to visit the original operational system to be able to determine them. Although the dates may be more recent than any significant code changes (due to commenting, or insignificant changes to constants), the earlier the dates are, the more they can bound for you the most recent version of Perl the program was developed for. See the version history in Chapter 7 to find out how to determine that version.