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expr1 & expr2
This operator (called “and”) returns the evaluation of expr1 if both expres‐
sions are true (i.e., neither expression evaluates to an empty string or zero).
Otherwise, it returns zero.
expr1 {=, >, >=, <, <=, !=} expr2
These operators return the results of an integer comparison if both argu‐
ments are integers; otherwise, they return the results of a string comparison.
The result of each comparison is 1 if the specified relation is true, or 0 if the
relation is false. (If you are doing string comparisons, they will be done in a
manner that’s consistent with the current local settings of your operating
system.)
Mathematical operators
Want to perform a calculation? You’ll want one of these:
expr1 {+, -} expr2
These operators return the results of the addition or subtraction of integer-
valued arguments.
expr1 {*, /, %} expr2
These return, respectively, the results of the multiplication, integer division,
or remainder of integer-valued arguments.
Regular expression operator
You can also use the regular expression operator in Asterisk:
Expressions and Variable Manipulation
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Some additional information about the peculiarities of the reg‐
ular expression operator in Asterisk can be found at Walter
Doekes’s website.
expr1 : expr2
This operator matches expr1 against expr2, where expr2 must be a regular
expression.2 The regular expression is anchored to the beginning of the
string with an implicit ^.3
If the pattern contains no subexpression, the number of matched characters
is returned. This will be 0 if the match failed. If the pattern contains a subex‐
pression -- \(...\) -- the string corresponding to \1 is returned. If the
match fails, the empty string is returned.
expr1 =~ expr2
This operator works the same as the : operator, except that it is not anchored
to the beginning.
Dialplan Functions
Dialplan functions allow you to add more power to your expressions; you can think
of them as intelligent variables. Dialplan functions allow you to calculate string
lengths, dates and times, MD5 checksums, and so on, all from within a dialplan
expression.
You’ll see usage of Playback(silence/1) throughout the examples
in this chapter. We are doing this as it will answer the line if it
hasn’t already been answered for us, and plays back some silence on
the line. This allows other applications such as SayNumber() to play
back audio without gaps.
Syntax
Dialplan functions have the following basic syntax:
FUNCTION_NAME(argument)
2 For more on regular expressions, grab a copy of the ultimate reference, Jeffrey E. F. Friedl’s Mastering Regular
Expressions (O’Reilly, 2006), or visit http://www.regular-expressions.info.
3 If you don’t know what a ^ has to do with regular expressions, you simply must read Mastering Regular
Expressions. It will change your life!
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Chapter 10: Deeper into the Dialplan
You reference a function’s name the same way as a variable’s name, but you reference
a function’s value with the addition of a dollar sign, an opening curly brace, and a
closing curly brace:
${FUNCTION_NAME(argument)}
Functions can also encapsulate other functions, like so:
${FUNCTION_NAME(${FUNCTION_NAME(argument)})}
^ ^ ^ ^ ^^^^