System variables retain information used by the system in some way. Many system variables affect the behaviour of primitive functions and operators to which they act as implicit arguments
System variables may be localised by inclusion in the header line of a defined function or in the argument list of the system function ⎕SHADOW. When a system variable is localised, it retains its previous value until it is assigned a new one. This feature is known as "pass-through localisation". The exception to this rule is ⎕TRAP.
A system variable can never be undefined. Default values are assigned to all system variables in a clear workspace.
| Name | Description | Scope |
|---|---|---|
| ⎕AVU | Atomic Vector – Unicode | Namespace |
| ⎕CT | Comparison Tolerance | Namespace |
| ⎕DCT | Decimal Comp Tolerance | Namespace |
| ⎕DIV | Division Method | Namespace |
| ⎕FR | Floating-Point Representation | Namespace |
| ⎕IO | Index Origin | Namespace |
| ⎕LX | Latent Expression | Workspace |
| ⎕ML | Migration Level | Namespace |
| ⎕PATH | Search Path | Session |
| ⎕PP | Print Precision | Namespace |
| ⎕PW | Print Width | Session |
| ⎕RL | Random Link | Namespace |
| ⎕RTL | Response Time Limit | Namespace |
| ⎕SM | Screen Map | Workspace |
| ⎕TNAME | Thread Name | Workspace |
| ⎕TRAP | Event Trap | Workspace |
| ⎕USING | Microsoft .NET Search Path | Namespace |
| ⎕WSID | Workspace ID | Workspace |
| ⎕WX | Window Expose | Namespace |
In other words, ⎕PATH and ⎕PW relate to the session. ⎕LX, ⎕SM, ⎕TRAP and ⎕WSID relate to the active workspace. All the other system variables relate to the current namespace.
| Session | Workspace | Namespace |
|---|---|---|
| ⎕PATH | ⎕LX | ⎕AVU |
| ⎕PW | ⎕SM | ⎕CT |
| ⎕TRAP | ⎕DCT | |
| ⎕WSID | ⎕DIV | |
| ⎕FR | ||
| ⎕IO | ||
| ⎕ML | ||
| ⎕PP | ||
| ⎕RL | ||
| ⎕RTL | ||
| ⎕USING | ||
| ⎕WX |
Note that the value assigned to a system variable must be appropriate; otherwise an error will be reported immediately.
⎕IO←3 DOMAIN ERROR ⎕IO←3 ^