USAGEMSG is the name of the constant being created:

use constant PI => 3.14;

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<<USAGE indicates the presence of a "here-doc". All the lines that follow are treated as a string literal. The string is ended by the keyword, alone on a line (no spaces or anything in front or after).

$Greeting = 'Hello';
$World    = 'Earth';
print(<<EOI, <<"End of Input", <<'EOI');
Foo!
Bar!
EOI
$Greeting
End of Input
$World
EOI

print(<<"==== End of Template ====");
<html>
... some long piece of hardcoded HTML ...
</html>
==== End of Template ====


# Prints:
# =======
# Foo!
# Bar!
# Hello
# $World
# <html>
# ... some long piece of hardcoded HTML ...
# </html>

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In reply to Re: Meaning of 'use constant USAGEMSG = > ...' by ikegami
in thread Meaning of 'use constant USAGEMSG = > ...' by rjsaulakh

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