You can "install" this plugin by placing it anywhere you want. If you use the nagios-plugins, the best place might be at /usr/lib/nagios/plugins/ or /usr/local/nrpe/libexec/
Make sure the Plugin is executeable:
chmod +x check_symlink
Possible NRPE command:
command[check_symlink]=/usr/local/nrpe/libexec/check_symlink -s /my/symlink
Possible Service
apply Service "check symlink" {
import "generic-service"
display_name = "Check Symlink"
check_command = "check_nrpe"
vars.sla = host.vars.sla
vars.nrpe_command = "check_symlink"
vars.alarm = "no"
assign where match("*symlink*", host.vars.services)
}