you can't really trust your path when running something that isn't an interactive shell. things like that typically don't read your /etc/profile, .profile, .bashrc, etc, so you are stuck with a default path the system gives you. of course, that should have /bin in it. you can always set your path at the beginning of your script:

$ENV{'PATH'} = "/bin:/usr/bin";
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it's a little surprising that it actually got that far, i would expect it to get the hostname long before it resorts to running external commands, from POSIX::uname or one of the other methods it employs.