Asterisk Dialplan Patterns
Extension Names and Patterns
Extension Names
Dialplan extensions can be simple numbers like "412" or "0". They can be alphanumeric names like "john" or "A93*". Although a typical telephone can't dial an extension called "john" (some can though), often your Dialplan logic will involve jumping from one extension to a different extension, and for those jumps you may define exension names with any name you like, as you don't wish them to be dialed directly.
Of course, touchtone telephones don't just have the digits 0 through 9, they also have * (star) and # ("pound" or "hash", depending on where in the world you live). And some touchtone (DTMF) telephones have the extra four "digits", A, B, C and D. If you have such handsets within your organization, there's nothing stopping you making use of those extra buttons for some special purpose of your own.
Note: To have an extension that is triggered by dialing the # symbol, you must use an extension pattern (see below). Asterisk does not recognize # as an ordinary 'digit', even though it appears on all DTMF telephones.
"Why do people in the US call the # symbol pound?" It doesn't seem to have anything to do with either money (e.g. the UK Pound Sterling) or with weight (lb).
Answer: Pound Sign
Answer: Pound Sign
Extension Patterns
Extension names are not limited to single specific extension "numbers". A single extension can also match patterns. In the extensions.conf file, an extension name is a pattern if it starts with the underscore symbol (_). In an extension pattern, the following characters have special meanings:
X matches any digit from 0-9
Z matches any digit from 1-9
N matches any digit from 2-9
[1237-9] matches any digit or letter in the brackets
(in this example, 1,2,3,7,8,9)
. wildcard, matches one or more characters
! wildcard, matches zero or more characters immediately
(only Asterisk 1.2 and later, see note)
Note: The exclamation mark wildcard, which is available only in Asterisk 1.2 and later, behaves specially — it will match as soon as can without waiting for the dialling to complete, but it will not match until it is unambiguous, and the number being dialled cannot match any other extension in the context. It was designed for use as follows, so that as soon as the digits dialled don't match '001800...' the outgoing telephone line will be picked up and overlap dialling will be used (with full audio feedback from 'earlyb3' etc.)
Context "outgoing":
Extension Description
_001800NXXXXXX Calls to USA toll-free numbers made by VoIP
_X! Other calls via normal telco, with overlap dial.
Example
Consider the following context:Context "routing":
Extension Description
_61XX Dallas Office
_63XX Dallas Office
_62XX Huntsville Office
_7[1-3]XX San Jose Office
_7[04-9]XX Los Angeles Office
This context, given the name "routing", sends calls to various servers according to their extension. This organization has decided that all of their telephone extensions will be 4 digits long. If a user dials an extension beginning with 61 or 63, it would be sent to the Dallas office; 62 would go to the Huntsville office; anything starting with 71, 72, or 73 would go to San Jose, and anything starting with 70, 74, 75, 76, 77, 78 or 79 would go to the Los Angeles office.
More Example Patterns
_NXXXXXX matches a NANP 7 digit telephone number such as 555-1212
_1NXXNXXXXXX matches an area code and phone number preceeded by a one such as 1-860-555-1212
_9011. matches any string of at least five characters that starts with 9011,
but it does not match the four-character string 9011 itself.
_9011! matches 9011 too
_# matches a single # keypress
Warning
Do not use a pattern of _. as this will match everything including Asterisk special extensions like i, t, h, etc. Instead use something like _X. or _X which will not match __special__ extensions..
Sort Order
If more than one pattern matches a dialed number, Asterisk may not use the one you expect. See:See Also
Asterisk | Configuration | The Dialplan - extensions.conf
Comments
333The + prefix
<p>
_+18001231234
<p>
this is useful if you're dialing from a phonebook such as from a sip enabled cell phone
333
333
> In asterisk 1.4 the special characters NXZ are case sensitive.
In asterisk 1.4 these characters are still case insensitive.
If you still want to use them do something like this exten => _next,1,No(can't match this!)
333More information
<P>Also, look out! the special characters Z X and N are not case sensitive (nxxnxxxxxx). These cavets bit me when trying to match the pattern _next-XXXX.</P>
_next-XXXX will match either next1234 or next-1234.<br/>
_next-XXXX will only match next-XXXX, my original goal.
333Thanks & "pound" story.
The other matter is the story behind the hash sign being referred as the "pound" sign. Your link was
the first time I had seen an explanation concerned with weights, but certainly makes sense. The story
I have always been told is that in the early days of trans-atlantic communications when most of the
business would have been concerning matters such as shipping or banking, the hash character was used
in North America to convey the meaning of UK pounds, and indeed when teleprinters arrived sending
"hash" from NA actually printed the pound character over in England......and vice versa.
The use of the word pound for money occurs in at least Egypt, Turkey, Cyprus and (before the Euro) Italy,
apart from the UK and derives from the fact that a pound of salt was used as a common trading element
many centuries ago.
Why is it that history only seems to be interesting after one has left school?