Backticks, like two-argument pipe opens, share the same problem: Undefined default shell behaviour. See Re: Ssh and qx. Using a perl SSH agent would entirely avoid the subprocess and the default shell. For a cross-platform, core-only solution, "Safe pipe opens" in perlipc explains how to avoid the default shell. The main trick in this case is to open STDIN from /dev/null in the child, then use multi-argument exec to prevent any interaction with the default shell.

Alexander