TOPS-20 Commands Reference Manual

ERUN

Runs a system program without disturbing the program already in memory by placing the program in an ephemeral fork.

Format

@ERUN (PROGRAM) filespec

where:

filespec

is the file specification of a system program.

Default dev:<directory> - SYS:

Default .typ - .EXE

Characteristics

Characteristics of an Ephemeral Fork

The ERUN command runs a program in an ephemeral fork. A program that runs in an ephemeral fork acts like an EXEC command (excluding those EXEC commands that run programs or otherwise affect memory). Ephemeral forks and EXEC commands share these characteristics:

They do not affect programs in memory. For example, if you exit a program and issue a SYSTAT command, or run a program in an ephemeral fork, neither the command nor the ephemeral fork will disturb the program in memory.

A program that runs ephemerally is always placed in a new fork.
They disappear when interrupted or when processing completes. For example, if you stop execution of a SYSTAT command or an ephemeral fork with CTRL/C, neither the command nor the ephemeral fork can be continued.

Whenever you stop or exit an ephemeral fork, the fork is automatically reset (cleared from memory).

Good candidates for ephemeral forks are programs that may have short execution times and simply display information in a manner similar to the INFORMATION and SYSTAT commands.

Related Commands

INFORMATION LOGICAL-NAMES	for examining the definition of SYS:
R	for running executable programs stored on SYS:
RUN	for running executable user programs
SET FILE EPHEMERAL	for giving a file a permanent ephemeral attribute
SET PROGRAM EPHEMERAL	for running a program in an ephemeral fork

Example

Display the status of the fork in memory with the INFORMATION FORK-STATUS command. Then, run a program in an ephemeral fork in order to preserve the state of your job's memory. Redisplay the fork status and note that the ephemeral program has been reset and has not replaced the original fork.

@INFORMATION FORK-STATUS
 => EMACS (1): HALT AT 50340, 0:00:03.6
@ERUN TERMSTAT
TERMSTAT>SHOW FREE TERMINALS

Lab  Terminals in use  Free terminals
---  ----------------  --------------
A          17               0
B          12               4

TERMSTAT>EXIT
@INFORMATION FORK-STATUS
 => EMACS (1): HALT at 50340, 0:00:03.6

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