in reply to External Dependencies on Unix Commands
Welcome to the age old headache of the shell programmer. Each utility can/will be in different locations among differing OS's, and their command switches and default output will certainly be different. I think this was a reason Perl became popular as a cross-OS scipting language, no?
Perhaps look into the Perl Power Tools, which are pure-Perl versions of many Unix utilities.
In Section Seekers of Perl Wisdom