Perl still supports the lower case forms of stdin, stdout and stderr:

$ perl -le'/std/i && print for keys %::'
stderr
stdout
stdin
STDOUT
STDERR
STDIN

$ perl -le'print stdout "Hello" or die $!'
Hello
[download]

But to get it to work with strict and warnings enabled is a bit more difficult:

$ perl -Mwarnings -Mstrict -le'print {*stdout} "Hello" or die $!'
Hello
$ perl -Mwarnings -Mstrict -le'print {\*stdout} "Hello" or die $!'
Hello
[download]