Datasets:
Squidnutz
/
extractedtest

Dataset card Data Studio Files
xet
 Community
1
text
stringlengths
0
152
It’s fairly unlikely (unless you have a typo) that you’d purposefully implement some‐
thing like our examples. However, when you perform math or a comparison with an
unset channel variable, this is effectively what you’re doing.
The examples we’ve used to show you how conditional branching works are not inva‐
lid. We’ve first initialized the variable and can clearly see that the channel variable
we’re using in our comparison has been set, so we’re safe. But what if you’re not
always so sure?
170
|
Chapter 10: Deeper into the Dialplan
In Asterisk, strings do not need to be double- or single-quoted like in many program‐
ming languages. In fact, if you use a double or single quote, it is a literal construct in
the string. If we look at the following snippets of an extension...
same => n,Set(TEST_1=foo)
same => n,Set(TEST_2='foo')
same => n,NoOp(Are TEST_1 and TEST_2 equiv? $[${TEST_1} = ${TEST_2}])
...we need to note that the value returned by our comparison in the NoOp() will not be
a value of 1 (values match; or true) the return value will be 0 (values do not match; or
false).
We can use this to our advantage when performing comparisons by wrapping our
channel variables in single or double quotes. By doing this we make sure even when
the channel variable might not be set, our comparison will be valid syntax.
In the following example, we would get an error:
exten => 212,1,NoOp()
same => n,GotoIf($[ ${TEST} != valid ]?error_handling)
same => n,Hangup() ; We're getting an error and ending up here
same => n(error_handling),Playback(goodbye)
same => n,Hangup()
However, we can circumvent this by wrapping what we’re comparing in extra charac‐
ters (in this case quotes). The same example, but made valid:
exten => 213,1,NoOp()
same => n,GotoIf($[ "${TEST}" != "valid" ]?error_handling)
same => n,Hangup()
same => n(error_handling),Playback(goodbye)
same => n,Hangup()
Even if ${TEST} hasn’t been set (in other words it does not exist and therefore has no
value), we’re still doing a comparison of something:
$["" != "valid"]
If you get into the habit of recognizing these situations and using the wrapping and
prefixing techniques we’ve outlined, you’ll write much safer dialplans.
Note again that the quote character doesn’t have any special meaning here. We used it
because it’s a logical character for this purpose. The following works too:
same => n,GotoIf($[_${TEST}_ != _valid_]?error_handling)
;OR
same => n,GotoIf($[AAAAA${TEST}AAAAA != AAAAAvalidAAAAA]?error_handling)
Not all characters will work, as some may have other meanings to Asterisk and cause
problems. Stay with the quote character and you should be fine.
The classic example of conditional branching is affectionately known as the “psycho-
ex” logic. If the caller ID number of the incoming call matches the phone number of
Conditional Branching
|
171
somebody you never want to talk to again, Asterisk gives a different message than it
ordinarily would to any other caller. While somewhat simple and primitive, it’s a good
example for learning about conditional branching within the Asterisk dialplan.
This example uses the CALLERID() function, which allows us to retrieve the caller ID
information on the inbound call. Let’s assume for the sake of this example that the
victim’s phone number is 888-555-1212:4
exten => 214,1,NoOp(CALLERID(num): ${CALLERID(num)} CALLERID(name): ${CALLERID(name)})
same => n,GotoIf($[ ${CALLERID(num)} = 8885551212 ]?reject:allow)
same => n(allow),Dial(${UserA_DeskPhone})
same => n,Hangup()
same => n(reject),Playback(abandon-all-hope)
same => n,Hangup()
In priority 1, we call the GotoIf() application. It tells Asterisk to go to priority label
reject if the caller ID number matches 8885551212, and otherwise to go to priority
label allow (we could have simply omitted the label name, causing the GotoIf() to
fall through).5 If the caller ID number matches, control of the call goes to priority
label reject, which plays back a subtle hint to the undesired caller. Otherwise, the
call attempts to dial the recipient on the channel referenced by the UserA_DeskPhone