Asterisk Standard Channel Variables

There are a number of variables that are defined or read by Asterisk. Here is a listing of them. More information is available in each application's help text. All these variables are in UPPER CASE only.
Variables marked with a * are builtin functions and can't be set, only read in the dialplan. Writes to such variables are silently ignored.

Variables present in Asterisk 1.8 and forward:

• ${CDR(accountcode)} * - Account code (if specified)
• ${BLINDTRANSFER} - The name of the channel on the other side of a blind transfer
• ${BRIDGEPEER} - Bridged peer
• ${BRIDGEPVTCALLID} - Bridged peer PVT call ID (SIP Call ID if a SIP call)
• ${CALLERID(ani)} * - Caller ANI (PRI channels)
• ${CALLERID(ani2)} * - ANI2 (Info digits) also called Originating line information or OLI
• ${CALLERID(all)} * - Caller ID
• ${CALLERID(dnid)} * - Dialed Number Identifier
• ${CALLERID(name)} * - Caller ID Name only
• ${CALLERID(num)} * - Caller ID Number only
• ${CALLERID(rdnis)} * - Redirected Dial Number ID Service
• ${CALLINGANI2} * - Caller ANI2 (PRI channels)
• ${CALLINGPRES} * - Caller ID presentation for incoming calls (PRI channels)
• ${CALLINGTNS} * - Transit Network Selector (PRI channels)
• ${CALLINGTON} * - Caller Type of Number (PRI channels)
• ${CHANNEL} * - Current channel name
• ${CONTEXT} * - Current context
• ${DATETIME} * - Current date time in the format: DDMMYYYY-HH:MM:SS (Deprecated; use ${STRFTIME(${EPOCH},,%d%m%Y-%H:%M:%S)})
• ${DB_RESULT} - Result value of DB_EXISTS() dial plan function
• ${EPOCH} * - Current unix style epoch
• ${EXTEN} * - Current extension
• ${ENV(VAR)} - Environmental variable VAR
• ${GOTO_ON_BLINDXFR} - Transfer to the specified context/extension/priority after a blind transfer (use ^ characters in place of | to separate context/extension/priority when setting this variable from the dialplan)
• ${HANGUPCAUSE} * - Asterisk cause of hangup (inbound/outbound)
• ${HINT} * - Channel hints for this extension
• ${HINTNAME} * - Suggested Caller*ID name for this extension
• ${INVALID_EXTEN} - The invalid called extension (used in the "i" extension)
• ${LANGUAGE} * - Current language (Deprecated; use ${LANGUAGE()})
• ${LEN(VAR)} - String length of VAR (integer)
• ${PRIORITY} * - Current priority in the dialplan
• ${PRIREDIRECTREASON} - Reason for redirect on PRI, if a call was directed
• ${TIMESTAMP} * - Current date time in the format: YYYYMMDD-HHMMSS (Deprecated; use ${STRFTIME(${EPOCH},,%Y%m%d-%H%M%S)})
• ${TRANSFER_CONTEXT} - Context for transferred calls
• ${FORWARD_CONTEXT} - Context for forwarded calls
• ${DYNAMIC_PEERNAME} - The name of the channel on the other side when a dynamic feature is used.
• ${DYNAMIC_FEATURENAME} The name of the last triggered dynamic feature.
• ${UNIQUEID} * - Current call unique identifier
• ${SYSTEMNAME} * - value of the systemname option of asterisk.conf
• ${ENTITYID} * - Global Entity ID set automatically, or from asterisk.conf

Variables present in Asterisk 11 and forward:

• ${AGIEXITONHANGUP} - set to 1 to force the behavior of a call to AGI to behave as it did in 1.4, where the AGI script would exit immediately on detecting a channel hangup
• ${CALENDAR_SUCCESS} * - Status of the CALENDAR_WRITE function. Set to 1 if the function completed successfully; 0 otherwise.
• ${SIP_RECVADDR} * - the address a SIP MESSAGE request was received from
• ${VOICEMAIL_PLAYBACKSTATUS} * - Status of the VoiceMailPlayMsg application. SUCCESS if the voicemail was played back successfully, {{FAILED} otherwise

https://wiki.asterisk.org/wiki/display/AST/Asterisk+Standard+Channel+Variables#