You do have some information. It would appear that you have four different locations a path could be present in. The following code uses that knowledge to pull out the user name from the proper location.

# Offsets into the path
my %indexes = (home => 1,
               Users => 2,
               Home => 1,
               export => 2);

# This would be one of the scalars you have access to (I'm using the
# CGI-BIN one in this code.)
my $path = '/home/username/public_html/cgi-bin/dir';

# Remove the leading / and then split up
my @pieces = split('/', substr($path, 1));

# Extract the user name information
my $username = $pieces[$indexes{$pieces[0]}];
print "$username\n";
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The %indexes variable holds the first part of the path as the key, and then the zero-based offset where the user name is stored after the path has been split.