This also has implications for the use of the SUPER:: qualifier
(see L<perlobj>).
-=head2 BEGIN, CHECK, INIT and END
-X<BEGIN> X<CHECK> X<INIT> X<END>
+=head2 BEGIN, UNITCHECK, CHECK, INIT and END
+X<BEGIN> X<UNITCHECK> X<CHECK> X<INIT> X<END>
-Four specially named code blocks are executed at the beginning and at the end
-of a running Perl program. These are the C<BEGIN>, C<CHECK>, C<INIT>, and
-C<END> blocks.
+Five specially named code blocks are executed at the beginning and at
+the end of a running Perl program. These are the C<BEGIN>,
+C<UNITCHECK>, C<CHECK>, C<INIT>, and C<END> blocks.
These code blocks can be prefixed with C<sub> to give the appearance of a
subroutine (although this is not considered good style). One should note
and run time. Once a C<BEGIN> has run, it is immediately undefined and any
code it used is returned to Perl's memory pool.
-It should be noted that C<BEGIN> code blocks B<are> executed inside string
-C<eval()>'s. The C<CHECK> and C<INIT> code blocks are B<not> executed inside
-a string eval, which e.g. can be a problem in a mod_perl environment.
+It should be noted that C<BEGIN> and C<UNITCHECK> code blocks B<are>
+executed inside string C<eval()>'s. The C<CHECK> and C<INIT> code
+blocks are B<not> executed inside a string eval, which e.g. can be a
+problem in a mod_perl environment.
An C<END> code block is executed as late as possible, that is, after
perl has finished running the program and just before the interpreter
is being exited, even if it is exiting as a result of a die() function.
-(But not if it's polymorphing into another program via C<exec>, or
+(But not if it's morphing into another program via C<exec>, or
being blown out of the water by a signal--you have to trap that yourself
(if you can).) You may have multiple C<END> blocks within a file--they
will execute in reverse order of definition; that is: last in, first
running something via C<system>).
X<$?>
-C<CHECK> and C<INIT> code blocks are useful to catch the transition between
-the compilation phase and the execution phase of the main program.
+C<UNITCHECK>, C<CHECK> and C<INIT> code blocks are useful to catch the
+transition between the compilation phase and the execution phase of
+the main program.
+
+C<UNITCHECK> blocks are run just after the unit which defined them has
+been compiled. The main program file and each module it loads are
+compilation units, as are string C<eval>s, code compiled using the
+C<(?{ })> construct in a regex, calls to C<do FILE>, C<require FILE>,
+and code after the C<-e> switch on the command line.
C<CHECK> code blocks are run just after the B<initial> Perl compile phase ends
and before the run time begins, in LIFO order. C<CHECK> code blocks are used
# begincheck
- print " 8. Ordinary code runs at runtime.\n";
+ print "10. Ordinary code runs at runtime.\n";
- END { print "14. So this is the end of the tale.\n" }
- INIT { print " 5. INIT blocks run FIFO just before runtime.\n" }
- CHECK { print " 4. So this is the fourth line.\n" }
+ END { print "16. So this is the end of the tale.\n" }
+ INIT { print " 7. INIT blocks run FIFO just before runtime.\n" }
+ UNITCHECK {
+ print " 4. And therefore before any CHECK blocks.\n"
+ }
+ CHECK { print " 6. So this is the sixth line.\n" }
- print " 9. It runs in order, of course.\n";
+ print "11. It runs in order, of course.\n";
BEGIN { print " 1. BEGIN blocks run FIFO during compilation.\n" }
- END { print "13. Read perlmod for the rest of the story.\n" }
- CHECK { print " 3. CHECK blocks run LIFO at compilation's end.\n" }
- INIT { print " 6. Run this again, using Perl's -c switch.\n" }
+ END { print "15. Read perlmod for the rest of the story.\n" }
+ CHECK { print " 5. CHECK blocks run LIFO after all compilation.\n" }
+ INIT { print " 8. Run this again, using Perl's -c switch.\n" }
- print "10. This is anti-obfuscated code.\n";
+ print "12. This is anti-obfuscated code.\n";
- END { print "12. END blocks run LIFO at quitting time.\n" }
+ END { print "14. END blocks run LIFO at quitting time.\n" }
BEGIN { print " 2. So this line comes out second.\n" }
- INIT { print " 7. You'll see the difference right away.\n" }
+ UNITCHECK {
+ print " 3. UNITCHECK blocks run LIFO after each file is compiled.\n"
+ }
+ INIT { print " 9. You'll see the difference right away.\n" }
- print "11. It merely _looks_ like it should be confusing.\n";
+ print "13. It merely _looks_ like it should be confusing.\n";
__END__
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