I'm currently trying to set the effective uid and gid to match the owner of a particular file as indicated by stat(), unfortunately it isn't working properly.

When I set the two values separately (gid first) it works as desired (setting the uid first doesn't allow the gid to change), but setting the variables at the same time doesn't set the egid properly.

$uid = 99;
# $> = 0
$gid = "99 2 99";
# $) = "0 1 0"
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$> = $uid;
$) = $gid;

# Current values are now:
# $> = 99
# $) = "0 1 0"
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$) = $gid;
$> = $uid;

# Current values are now:
# $> = 99
# $) = "99 2 99"
# Which is the desired outcome
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($>, $)) = ($uid, $gid;)

# Current values are now:
# $> = 99
# $) = "0 99 2"
# The other groups section has been successfully changed,
# but the actual effective gid has not.
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Is it somehow possible to assign to the effective gid and uid at the same time? Obviously I can split it into two steps, but I would prefer to assign both at once if possible (and this seems a strange way to behave).

EDIT
This is Perl 5.8.0 running on Redhat 9