special_functions.pl

use strict;
use warnings;

# This is just the demo of how special functions work inside perl code
# https://perldoc.perl.org/perlmod.html#BEGIN%2c-UNITCHECK%2c-CHECK%2c-INIT-and-END

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";