Writing portable scripts for UNIX and Linux is fairly easy – Korn shell is everywhere, and ksh scripts work the same and have the same basic tools available (sed, awk, pipes, etc.).
What about writing portable scripts to work on UNIX, Linux, and OpenVMS? UNIX and Linux are similar enough that things will work across the different platforms – the same holds for the BSD platforms and for Windows with the Cygwin utilities. But radically different platforms such as OpenVMS require a different approach.
The first thing I did in looking at OpenVMS was to search out the languages and utilities that were available. HP offers a number of open source tools, and has Freeware CDROMs available as well. SAIC has a large OpenVMS archive, including the contents of the HP Freeware CDROMs.
Under OpenVMS, I found these languages available:
- Java (built-in)
- GNU awk
I doubt that Java would be used for scripting purposes, but it is becoming ubiquitous and if it is well-known by the scripter, it is possible that it could be used.
However, the other (add-on) alternatives seem to be much more likely. Perl, Python, GNU awk, and tcl have extensive capabilities, and with tk visual displays are possible. My main choice would probably be Perl.
The Perl portability documentation goes into complete detail about the various points that may trip a programmer up; in short, several of the main points cover:
- Data representation (high-endian order? low-endian order? line terminator?)
- File path representation
- Character sets and encoding (including order)
- Time and date representation
The best thing to do is to following the guidelines in the Perl portability document (even if using other languages) and to then test the portable code on all systems affected. Only in extreme circumstances should code be written specifically to the target system and selected based on target OS type. Better to make it portable at its core.