( undef, $userid ) = split /[\\\/]/, $ENV{'REMOTE_USER'};
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your split works in a scalar context, so you need:

(undef, $userid) = split "/", ....
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Which doesn't match both cases, so you need:

(undef, $userid) = split "/|\\\\", $ENV{REMOTE_USER};
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Yes, you need 4 slashes.

Also in your regex you need to escacpe the backslash:

$username =~ m#(cyc)/|\\(.*)#;
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(undef, $userid) = split(qr{(?:/|\\)}, $ENV{'REMOTE_USER'});
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# Alternation with non-capturing clustering (?:foo)
(undef, $userid) = split(qr{(?:/|\\)}, $ENV{'REMOTE_USER'});

# Alternation without clustering
(undef, $userid) = split(qr{\\|/}, $ENV{'REMOTE_USER'});

# Character class including '\' and '/'
(undef, $userid) = split(qr{[\\/]}, $ENV{'REMOTE_USER'});
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You don't need to do that, because the delimiter is included in the result if the pattern has parenthese.

print join ":", split "-", "1-2-3-4";

# as opposed to:

print join ":", split "(-)", "1-2-3-4";
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--
Leviathan.

I initially reacted to this line in the OP:

$username =~ /(cyc(\|\/)(.*?)/;
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Which had several problems.
• Does not assign the resulting match
• Should use non-capturing clustering or a character class for the '/' or '\'
• Has an extra opening paren
• Uses non-greedy match to select the username
These would work:

($username) = $ENV{REMOTE_USER} =~ /cyc(?:\\|\/)(.+)/;
($username) = $ENV{REMOTE_USER} =~ /cyc[\/\\](.+)/;
# And to cleanup a little
($username) = $ENV{REMOTE_USER} =~ m{cyc(?:\\|/)(.+)};
($username) = $ENV{REMOTE_USER} =~ m{cyc[/\\](.+)};
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But not having coffee yet I corrected the split version instead.

It's also worth nothing that split("\\|/","a|/b") does not work as one might think.

perl -e 'my ($a,$b) = split("\\|/","a/b"); print "a:$a\nb:$b\n"'   
a:a/b
b:
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This happens because that pattern is actually looking for a literal '|/', as shown here:

perl -MO=Deparse -e 'my ($a,$b) = split("\\|/","a/b");'           
my($a, $b) = split(m[\|/], 'a/b', 3);

perl -e 'my ($a,$b) = split("\\|/","a|/b"); print "a:$a\nb:$b\n"' 
a:a
b:b
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