JMeter functions are special values that can populate fields or any sampler or other element in the test plan. They take the following form:

${__functionName(var1,var2,var3)}

Here, __functionName matches any of the many function names JMeter offers. Parentheses surround the parameters sent to the function, which can vary from function to function. Functions with no parameters don't need the parentheses, for example, ${__threadNum}. A list of all available functions can be found on JMeter's website at http://jmeter.apache.org/usermanual/functions.html. Functions are divided into seven main categories. They are given here along with their examples:

Functions can prove useful in certain situations...