String variables (meaning variables that contain text and not numbers) should be defined using double quotes, though Asterisk will still accept them without double quotes - the following two entries are functionally identical:

exten => 1234,1,Set(FRUIT=Apple)
exten => 1234,2,Set(FRUIT="Apple")

If the string contains commas or spaces, you must use double quotes:

exten => 1234,1,Set(FRUITTYPES="Apple, Pear, etc.")

This is why it is a good idea to get into the habit of using them for any string variables you define.

Sometimes a variable will contain reserved characters (characters that have special functions and are interpreted differently). For example, if you want to variable to contain the underscore character ("_") you must use an "escape" character to tell the dialplan interpreter that it should ignore the reserved character. The following characters must be escaped when used in a variable:

[ ] $ " \

The escape character in extensions.conf is "\" (backslash):

Example:

exten => 1234,1,Set(AMOUNT="\$10.00")

Similarly, if you want to use the backslash character in a variable, you must escape it:

exten => 1234,1,Set(ROOMNUMBER="48\\10")

If a variable contains an integer, it can have no more than 18 digits. Anything larger will cause an error which will be recorded in the log file.

	If you need to work with larger integers or floating point numbers, you can use an AGI script (see ???).

Set(<variable1>=<value1>[,<variable2>=<value2>][,<option>])

Setting option g makes the variable global; without it, the variable is treated as a local channel variable.

Example:

; Set a global variable:
exten => 10,1,Set(RINGTIME=90,g)

; Set a local channel variable:
exten => 10,2,Set(FAVORITEFRUIT="Apple")

; Set two channel variables at once:
exten => 10,3,Set(VAR1=10,VAR2=23)

; Print variables to the CLI
exten => 10,4,NoOp(RINGTIME = ${RINGTIME})
exten => 10,5,NoOp(FAVORITEFRUIT = ${FAVORITEFRUIT})
exten => 10,6,NoOp(VAR1 = ${VAR1})
exten => 10,7,NoOp(VAR2 = ${VAR2})

Sometimes you want to have a channel variable persist into the spawned channel. You can do this by prefixing the variable with an "_" (underscore) character. When the variable is inherited by the spawned channel, Asterisk automatically removes the prefix. This ensures that the variable is inherited only once.

Example:

exten => 1234,1,Set(_CAKE="Marble cake")

If you need unlimited inheritance of a channel variable, you can do this by prefixing the variable with two "_" (underscore) characters. Variables prefixed in this way will always be inherited by spawned channels.

	Asterisk makes no distinction between variable names that are preceded with an underscore and those that are not. In the example below, a variable with multi-level inheritance ("__CAKE") is rendered uninheritable by the subsequent entry: exten => 1234,1,Set(__CAKE="Marble cake") exten => 1234,n,Set(CAKE="Marble cake")

Example:

exten => 1234,1,Set(__CAKE="Sponge cake")

When calling an inherited variable, it doesn't matter if it is called with a prefix or not. These entries will give the same output in the CLI:

exten => 1234,1,NoOp(${__CAKE})
exten => 1234,n,NoOp(${CAKE})

In general, a string consistes of a sequence of individual characters. The size of a string is determined by the number of characters contained in it. For example, the string "apple tree" has 10 characters (we must include the space). Any string can be broken into substrings. For example, "apple", "tree", "app" and "le tre" are all valid substrings of "apple tree". In theory, a string can be of any length; this entire book could be contained in a single string, though it would be impractical. Manipulation of strings is an important technique in programming applications. Asterisk lets you manipulate strings and substrings using the : (colon) character. Using the : character, you can extract a specified portion of an existing string variable.

${VARIABLENAME[:start[:length]]}

Examples

Many telephone systems require that a prefix digit be dialled in order to get an outside line (In North America, this is usually "9"). The target number, however, cannot include this prefix digit. If we dial 9-1-202-7075000, we can store the actual outside number in the ${OUTGOINGNUMBER} using the following dialplan entry.^[13]

exten => _0X.,1,Set(OUTGOINGNUMBER=${EXTEN:1})

If the length option is omitted, the rest of the string is taken automatically.

What if we only need the last seven digits of the dialed number? I this case we use a negative number for the start parameter. The following entry would store 7075000 from our example above in the variable ${LOCALNUMBER}.^[14]

exten => _0X.,1,Set(LOCALNUMBER=${EXTEN:-7})

We can also capture just the area code:

exten => _0X.,1,Set(AREACODE=${EXTEN:2:3})

	Obviously, readers in other parts of the world (e.g. the United Kingdom, Australia, or elsewhere) will have different national dialplans which impact how outside numbers should be processed. Some countries have area and city codes which are variable in length; in those cases, this kind of number filtering will not be practical.

Here, then, is how we might extract useful information from a dialed number:

exten => _9X.,1,Set(AREACODE=${EXTEN:2:3})
exten => _9X.,n,Set(LOCALNUMBER=${EXTEN:5})