When dealing w/ a heredoc string you put your "or die" w/ the original print statment:

print FILE <<UNTIL_I_SAY_STOP or die "ERROR Writing to FILE: $!";
 blah, blah, blah
UNTIL_I_SAY_STOP
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It works similarly whenever you want to do something else after the heredoc...

my $sub=substr(<<EOT,3,3);
abc123def
EOT
print "sub=\"$sub\"\n";
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prints out 123.

You can even get fancy (or hard to read depending on your preference) and use multiple heredocs in the same call:

print <<EOT1,<<EOT2;
foo
EOT1
bar
EOT2
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