Example:
OR(
AND(
ISPICKVAL( Country_Code__c , “USA”),NOT( REGEX( Pincode__c , “\d{5}(-\d{4})?”) )
),
AND(
ISPICKVAL( Country_Code__c , “MEX”), NOT(REGEX( Pincode__c , “\d{5}”)), NOT(REGEX( Pincode__c , “\d{6}”))
),
AND(
ISPICKVAL( Country_Code__c , “AUS”), NOT(REGEX( Pincode__c , “\d{4}”))
),
AND(
ISPICKVAL( Country_Code__c , “CAN”), NOT(REGEX( Pincode__c , “[a-zA-Z]{1}[0-9]{1}[a-zA-Z]{1}\s[0-9]{1}[a-zA-Z]{1}[0-9]{1}”))
),
AND(
ISPICKVAL( Country_Code__c , “ARG”), NOT(REGEX( Pincode__c ,
“[a-zA-Z]{1}\d{4}[a-zA-Z]{3}”)),NOT(REGEX( Pincode__c , “\d{4}”))
)
)
