perl lifecycle test

lifecycle.pl

#!/usr/bin/perl
# https://perldoc.perl.org/perlmod#BEGIN%2C-UNITCHECK%2C-CHECK%2C-INIT-and-END

# Try these:
# perl ./lifecycle.pl
# perl -c ./lifecycle.pl

package le_module;
print         " 9.a. module print\n";

BEGIN { print " 0.a. module BEGIN\n" }
END {   print "17. module END\n" }

INIT { print " 6.a. module INIT\n" }

sub import {
    print     " 0.b. module import\n";
}

package lifecycle;

BEGIN { 'le_module'->import; } # nearly equivalent of `use le_module;`

# begincheck

print         "10. Ordinary code runs at runtime.\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         "11.   It runs in order, of course.\n";

BEGIN { print " 1. BEGIN blocks run FIFO during compilation.\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         "12.   This is anti-obfuscated code.\n";

END { print   "14. END blocks run LIFO at quitting time.\n" }
BEGIN { print " 2.   So this line comes out second.\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         "13.   It only _looks_ like it should be confusing.\n";