nagios :Understanding Macros and How They Work
Example 1: Host Address Macro
When you use host and service macros in command definitions, they refer to values for the host or service for which the command is being run. Let's try an example. Assuming we are using a host definition and a check_ping command defined like this:
define host{
host_name linuxbox
address 192.168.1.2
check_command check_ping
...
}
define command{
command_name check_ping
command_line /usr/local/nagios/libexec/check_ping -H $HOSTADDRESS$ -w 100.0,90% -c 200.0,60%
}
the expanded/final command line to be executed for the host's check command would look like this:
/usr/local/nagios/libexec/check_ping -H 192.168.1.2 -w 100.0,90% -c 200.0,60%
Pretty simple, right? The beauty in this is that you can use a single command definition to check an unlimited number of hosts. Each host can be checked with the same command definition because each host's address is automatically substituted in the command line before execution.
Example 2: Command Argument Macros
You can pass arguments to commands as well, which is quite handy if you'd like to keep your command definitions rather generic. Arguments are specified in the object (i.e. host or service) definition, by separating them from the command name with exclamation points (!) like so:
define service{
host_name linuxbox
service_description PING
check_command check_ping!200.0,80%!400.0,40%
...
}
In the example above, the service check command has two arguments (which can be referenced with $ARGn$ macros). The $ARG1$ macro will be "200.0,80%" and $ARG2$ will be "400.0,40%" (both without quotes). Assuming we are using the host definition given earlier and a check_ping command defined like this:
define command{
command_name check_ping
command_line /usr/local/nagios/libexec/check_ping -H $HOSTADDRESS$ -w $ARG1$ -c $ARG2$
}
the expanded/final command line to be executed for the service's check command would look like this:
/usr/local/nagios/libexec/check_ping -H 192.168.1.2 -w 200.0,80% -c 400.0,40%