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Apache Today: The Perl Basics You Need To Know

Aug 02, 2000, 15:07 (0 Talkback[s])
(Other stories by Stas Bekman)

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"Before I delve into the details of mod_perl programming in the future articles it's probably a very good idea to review some very important Perl basics. You will discover these invaluable when you start coding for mod_perl. I will start with pure Perl notes and gradually move to explaining the peculiarities of coding for mod_perl, presenting the traps one might fall into and explaining things obvious for some of us but may be not for the others."

"It helps when you code your application in a structured way, using the perl packages, but as you probably know once you start using packages it's much harder to share the variables between the various packagings. ... Of course, using object-oriented (OO) programming is the best way to provide an access to variables through the access methods. But if you are not yet ready for OO techniques you can still benefit from using the techniques I'm going to talk about."

"Special Perl variables like $| (buffering), $^T (script's start time), $^W (warnings mode), $/ (input record separator), $\ (output record separator), and many more are all true global variables; they do not belong to any particular package (not even main::) and are universally available. This means that if you change them, you change them anywhere across the entire program; furthermore you cannot scope them with my(). However you can local()ise them which means that any changes you apply will only last until the end of the enclosing scope. In the mod_perl situation where the child server doesn't usually exit, if in one of your scripts you modify a global variable it will be changed for the rest of the process's life and will affect all the scripts executed by the same process. Therefore, localising these variables is highly recommended, I'd say mandatory."

"When using a regular expression that contains an interpolated Perl variable, if it is known that the variable (or variables) will not change during the execution of the program, a standard optimization technique is to add the /o modifier to the regex pattern. This directs the compiler to build the internal table once, for the entire lifetime of the script, rather than every time the pattern is executed."

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