Not a one-liner, but fairly straightforward (untested):

sub ltostr {
    my ($num, $base) = @_;
    Carp::croak("Invalid base $base") if $base < 2 || $base > 36;
    my $neg = $num < 0;
    $num = -$num if $neg;
    my $str = '';
    do {
        $str = ( '0'..'9', 'a'..'z' )[ $num % $base ] . $str;
        $num = int( $num / $base );
    } while $num;
    $str = "-$str" if $neg;
    return $str;
}
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