It will actually be run straightaway, as soon as the block is reached by the compiler. So whatever lines are below the BEGIN { } won't have even been seen at the time of its execution.
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from http://perldoc.perl.org/perlmod.html
A BEGIN code block is executed as soon as possible, that is, the moment it is completely defined, even before the rest of the containing file (or string) is parsed. You may have multiple BEGIN blocks within a file (or eval'ed string); they will execute in order of definition. Because a BEGIN code block executes immediately, it can pull in definitions of subroutines and such from other files in time to be visible to the rest of the compile and run time. Once a BEGIN has run, it is immediately undefined and any code it used is returned to Perl's memory pool.
So, yes, a BEGIN block will run when it is encountered. But it will only run once - that part of my statement is correct. But it does appear that you can intersperse BEGIN blocks within the code and they will run essentially as the code "compiles". that is cool Perl thing.
When I have used BEGIN{}, I have never interspersed these within the code, but rather have put these at the "end" of the code. In other words, this is initialization code that should be executed before the main code - not interspersed.
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