3.3. Variables

Identifiers for variables and functions are alphanumeric sequences, and may include the underscore (_) and the dollar sign ($) characters. They may not start with a plain digit. Each variable is by default local to the probe or function statement block where it is mentioned, and therefore its scope and lifetime is limited to a particular probe or function invocation. Scalar variables are implicitly typed as either string or integer. Associative arrays also have a string or integer value, and a tuple of strings or integers serves as a key. Arrays must be declared as global. Local arrays are not allowed.

The translator performs type inference on all identifiers, including array indexes and function parameters. Inconsistent type-related use of identifiers results in an error.

Variables may be declared global. Global variables are shared among all probes and remain instantiated as long as the SystemTap session. There is one namespace for all global variables, regardless of the script file in which they are found. Because of possible concurrency limits, such as multiple probe handlers, each global variable used by a probe is automatically read- or write-locked while the handler is running. A global declaration may be written at the outermost level anywhere in a script file, not just within a block of code. Global variables which are written but never read will be displayed automatically at session shutdown. The following declaration marks var1 and var2 as global. The translator will infer a value type for each, and if the variable is used as an array, its key types.

global var1[=<value>], var2[=<value>]