Pattern to fetch Indices Identifier ($SUBJECT_ID):$SUBJECT_ID defines indices identifier i.e. unique substring of a vector. You can provide regular expressions to fetch a unique substring from every vector. This helps you to identify every vector uniquely.

• Use cases for $SUBJECT_ID:
1. You can provide $SUBJECT_ID in subject, pre-text and post-text of an Email.
2. You can provide $SUBJECT_ID in the message of the rule for the SNMP trap.
3. You can provide $SUBJECT_ID in the message field of the rule for Alert-Extension.
If you use any of the above use cases then $SUBJECT_ID is replaced by such substring from vector which is the outcome of given regular expression after compilation on that vector.

• Example:1
If you have provided regular-expression "[0-9]{3}$"
And the alert got triggered in the vector "AppTier>Server000703"
And you have given $SUBJECT_ID in the subject of email
Then, in the subject of the email, "703" is displayed instead of $SUBJECT_ID

• Example:2
If you have provided regular-expression "(?<=>h121580vaps)\d+"
And alert got triggered in the vector "ATG-OPEN-API-REST-BURST>h121580vaps2360>kls-rest-43"
And you have given $SUBJECT_ID in the subject of email
Then, in the subject of the email, "2360" is displayed instead of $SUBJECT_ID