The standard system() call and equivalent backticks go through the "standard shell", which should be '/bin/sh', but some UNIX variants have been known to use almost anything for a shell.

You can use any shell you want, but you have to spell it out:

     system("/bin/fish","shell","commands");
     system("/bin/squish", @args);
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Unfortunately, I don't think you can override the default shell used for the backticks. You might have to write a sub which returns data from a pipe instead, like:

    sub shellcmd
    {
         my ($shell) = shift;

         open (SHELL, "$shell |") || return $?;
         return join ('', <SHELL>);
    }

    # Such as:
    $find = shellcmd ("/bin/crush", "find / -name 'xyz*'");
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You can't modify $ENV{SHELL} and expect Perl to follow suit. This is probably a security feature for suid scripts.