Functions are often used in conjunction with the Set() application to either get or set the value of a variable. As a simple example, let's look at the LEN() function. This function calculates the string length of its argument. Let's calculate the string length of a variable and read back the length to the caller:

    exten => 123,1,Set(TEST=example)
    exten => 123,n,SayNumber(${LEN(${TEST})})

The above example would evaluate the string example as having seven characters, assign the number of characters to the variable length, and then speak the number to the user with the SayNumber() application.

Let's look at another simple example. If we wanted to set one of the various channel timeouts, we could use the TIMEOUT() function. The TIMEOUT() function accepts one of three arguments: absolute, digit, and response. To set the digit timeout with the TIMEOUT() function, we could use the Set() application, like so:

    exten => s,1,Set(TIMEOUT(digit)=30)

Notice the lack of ${ } surrounding the function. Just as if we were assigning a value to a variable, we assign a value to a function without the use of the ${ } encapsulation.

A complete list of available functions can be found by typing core show functions at the Asterisk command-line interface. You can also look them up in Appendix F.