arrays associative arrays associative arrays introduction SystemTap also supports the use of associative arrays. While an ordinary variable represents a single value, associative arrays can represent a collection of values. Simply put, an associative array is a collection of unique keys; each key in the array has a value associated with it. associative arrays introduction key pairs key pairs introduction arrays associative arrays introduction unique keys unique keys introduction arrays associative arrays introduction associated values associated values introduction arrays associative arrays introduction index expression index expression introduction arrays Since associative arrays are normally processed in multiple probes (as we will demonstrate later), they are declared as global variables in the SystemTap script. The syntax for accessing an element in an associative array is similar to that of awk, and is as follows: associative arrays introduction syntax syntax introduction arrays format introduction arrays array_name[index_expression] Here, the array_name is any arbitrary name the array uses. The index_expression is used to refer to a specific unique key in the array. To illustrate, let us try to build an array named foo that specifies the ages of three people (i.e. the unique keys): tom, dick, and harry. To assign them the ages (i.e. associated values) of 23, 24, and 25 respectively, we'd use the following array statements: associative arrays introduction example example introduction arrays foo["tom"] = 23 foo["dick"] = 24 foo["harry"] = 25 You can specify up to nine index expressons in an array statement, each one delimited by a comma (,). This is useful if you wish to have a key that contains multiple pieces of information. The following line from uses 5 elements for the key: process ID, executable name, user ID, parent process ID, and string "W". It associates the value of devname with that key. device[pid(),execname(),uid(),ppid(),"W"] = devname All associate arrays must be declared as global, regardless of whether the associate array is used in one or multiple probes.