[Asterisk-Users] Undocumented "exten" syntax?

[Asterisk]

John Goerzen wrote:
> Over at http://www.voip-info.org/wiki-Asterisk+tips+911, I see these
> extensions.conf lines:
> 
> exten => s,1,SetVar(SET_EMERG_FLAG=0)
> exten => s,n(checkavail),ChanIsAvail(${EMERGENCY_TRUNK})
> exten => s,n,SetGlobalVar(EMERGENCY=1)
> exten => s,n,SetVar(SET_EMERG_FLAG=1)
> exten => s,n(dial),Dial(${EMERGENCY_TRUNK}/${EMERGENCY_NUM})
> exten => s,s+2(trunkbusy),GotoIf($[${EMERGENCY} = 1]?inprogress)
> 
> Now, I have several questions:
> 
>  * What is the "n" priority and how can they use it for several
>    different items?  Don't they need an increasing integer there?

n stands for the next available sequence after the previous one. This is 
  used so that you can insert a step in the dial plan without having to 
renumber all the following steps.

> 
>  * What is the "(checkavail)" doing?
> 

Thats a label. If you use n, you lose the ability to say "goto 102"

>  * What does "s+2" mean?

ok. That's fooled me.

> 
> I've tried looking in docs and the wiki but can't figure it out.
> 
> Thanks!
> 
> -- John
> 
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