Question regarding the function of check-snmp plugin

Sam Shabani <saam.shabani-FFYn/[email protected]> Mon, 16 Nov 2015 20:30:11 +0000 (UTC)
Newsgroups gmane.network.nagios.plugins
Message-ID <632372519.4661238.1447705811190.JavaMail.yahoo__28461.1489660621$1447707416$gmane$org@mail.yahoo.com>
Hi Dear,
If the result of snmpget command was string , Could you please tell me how the check-snmp plugin works? It sounds that  the string convert to interger but  how does it find the integer parts of string ? 
The following is the output : [root@localhost tmp]# /usr/lib64/nagios/plugins/check_snmp -H IP_ADDRESS -o .1.3.6.1.4.1.2.3.51.2.2.3.1.0 -C public SNMP OK - "    56% of maximum" | [root@localhost tmp]# /usr/lib64/nagios/plugins/check_snmp -H IP_ADDRESS -o .1.3.6.1.4.1.2.3.51.2.2.3.1.0 -C public -w 50SNMP WARNING - *56* | iso.3.6.1.4.1.2.3.51.2.2.3.1.0=56;50;;


Thanks a lot ,sam,