Bloody instructions which, being taught ,
return to plague their inventor
William Shakespeare
Macbeth, Act 1, Scene 7
The single most important recommendation about Perl's built-in functions is also the simplest: use them.
If Perl already provides a way to solve your problem, and that way is integrated into the language itself, then it doesn't make sense to reinvent it. It's likely that Perl's built-in solution is faster and far better debugged than anything you'll have time to write yourself.
However, some of Perl's built-in functions are sufficiently complex, and their behaviour sufficiently subtle, that there are still right and wrong ways to use them. This chapter explores some of these ways.