An alternative to $ENV{HOME} is (getpwuid $>)[7]. I don't know which might be better, if one is. If you're in a shell environment and $HOME either doesn't exist or is stripped, then that could be an issue. For example, I do this a lot:

my $HOME = (getpwuid $>)[7];
my $ssh_dir = qq{$HOME/.ssh};
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I wanted to add, that getpwuid is probably more reliable when you're doing stuff with setuid; in the example above, $> is the effective user; $< being the real user. I don't think invoking it updates $ENV in any way, like su - OTHER_USER would directly in the shell before invoking the script in question (certainly doing this in the script would not effect the parent process's %ENV at all). perlsec looks informative regarding this. But it just depends on what OP is doing. If there is no reason or need to use setuid (or setguid), then $ENV{HOME} is probably fine.