Zapowork: \A..\z is just as efficient as ^..$

\A..\z should be used to anchor a pure string, wheras ^..$ should be used to anchor a line. For most cases, the difference is subtle enough that, virtually, there is no difference (this is why cookbook examples, and a lot of existing code is able to get away with never using \A..\z). Still, it is proper to be accurate. If it is not expected, or acceptable for a string to end with '\n', \z should be used instead of $.

For example:

if ($ARGV[0] =~ /^-o$/) { ... }

Will match "-o" or "-o\n". For command line arguments, "-o\n" should not be allowed. The more accurate expression is:

if ($ARGV[0] =~ /\A-o\z/) { ... }

The reason I am so rigid about this point is that I have been hit by the difference in production code. I am now very strict about use \A..\z for strings and ^..$ for lines.

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