HP OpenVMS Systems Documentation

HP OpenVMS DCL Dictionary

Returns a process identification (PID) number and updates the context symbol to point to the current position in the system's process list.

Format

F$PID (context-symbol)

Return Value

Argument

context-symbol

Specifies a symbol that DCL uses to store a pointer into the system's list of processes. The F$PID function uses this pointer to return a PID.

Specify the context symbol by using a symbol. The first time you use the F$PID function in a command procedure, you should use a symbol that is either undefined or equated to the null string ("") or a context symbol that has been created by the F$CONTEXT function.

If the context symbol is undefined or equated to a null string, the F$PID function returns the first PID in the system's process list that it has the privilege to access. That is, if you have GROUP privilege and if the context symbol is null or undefined, the F$PID function returns the PID of the first process in your group. If you have WORLD privilege, the F$PID function returns the PID of the first process in the list. If you have neither GROUP nor WORLD privilege, the F$PID returns the first process that you own. Subsequent calls to F$PID return the rest of the processes on the system you are accessing.

If the context symbol has been created by the F$CONTEXT function, the F$PID function returns the first process name in the system's process list that fits the criteria specified in the F$CONTEXT calls. Subsequent calls to F$PID return only the PIDs of those processes that meet the selection criteria set up by the F$CONTEXT function and that are accessible to your current privileges.

Description

The F$PID function returns a process identification (PID) number and updates the context symbol to point to the current position in the system's process list. You can step through all the processes on a system, or use the lexical function F$CONTEXT to specify selection criteria. The function F$CONTEXT is not required.

The PIDs returned by the F$PID function depend on the privilege of your process. If you have GROUP privilege, the F$PID function returns PIDs of processes in your group. If you have WORLD privilege, the F$PID function returns PIDs of all processes on the system. If you lack GROUP or WORLD privilege, the F$PID function returns only those processes that you own.

The F$CONTEXT function enables the F$PID function to retrieve processes from any node in a mixed-architecture OpenVMS Cluster system.

The first time you use the F$PID function, use a symbol that is either undefined or equated to the null string or to a context symbol that has been created by the F$CONTEXT function. This causes the F$PID function to return the first PID in the system's process list that you have the privilege to access. It also causes the F$PID function to initialize the context-symbol argument.

Once the context-symbol argument is initialized, each subsequent F$PID returns the next PID in sequence, using the selection criteria set up by the F$CONTEXT function, if any, and updates the context symbol. After the last PID in the process list is returned, the F$PID function returns a null string.

Example

$ CONTEXT = ""
$ START:
$     PID = F$PID(CONTEXT)
$     IF PID .EQS. "" THEN EXIT
$     SHOW SYMBOL PID
$     GOTO START
      

This command procedure uses the F$PID function to display a list of PIDs. The assignment statement declares the symbol CONTEXT, which is used as the context-symbol argument for the F$PID function. Because CONTEXT is equated to a null string, the F$PID function returns the first PID in the process list that it has the privilege to access.

The PIDs displayed by this command procedure depend on the privilege of your process. When run with GROUP privilege, the PIDs of users in your group are displayed. When run with WORLD privilege, the PIDs of all users on the system are displayed. Without GROUP or WORLD privilege, only those processes that you own are displayed.