TOPS-20 Commands Reference Manual

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POP

Terminates the current level of TOPS-20 and returns you to its superior process.

Format

@POP (COMMAND LEVEL)

Characteristics

POP the Opposite of PUSH

You can do one and only one POP command for every previous PUSH command. Giving too many POP commands will cause an error message to be printed on your terminal.

Job Parameters Affected by POP

As soon as you complete a valid POP command at some level of TOPS-20, you give up the copy of memory for that level of TOPS-20 and any program you were running. Any defaults established at that level (such as default filespecs for LOAD-class and EDIT-class commands, defaults specified by SET DEFAULT commands) are cancelled as well. If POP returns you to a higher level of TOPS-20, all these parameters revert to any values established at that higher level.

Special Cases

Returning to Other Programs With POP

The POP command usually returns you to the level of TOPS-20 from which you gave a previous PUSH command. But a few system programs such as PTYCON and OPR, also allow you to give PUSH to get a new level of TOPS-20. Giving the POP command to this level of TOPS-20 returns you to that program.

Effect on Memory and Terminal

The POP command clears memory, terminates the current level of TOPS-20, and returns your terminal to the previous TOPS-20 command level (but see Special Cases, above). Memory for the previous TOPS-20 command level is not affected by this action.

Related Commands

CONTINUE	for resuming execution of a program in memory
INFORMATION SUPERIORS	for information on the number of forks that are superior to the current EXEC level
PUSH	for obtaining a new level of TOPS-20

Examples

Give the POP command to return to a higher level of the TOPS-20 command processor (EXEC).
```
@POP
```
Run a program and halt it with CTRL/Cs. Give a CONTINUE STAY command to resume its execution, and then the PUSH command for a new level of TOPS-20. Run another program at this lower level, then use the POP command to return to the first level; in this case you return before receiving the final message of the first program.
```
@RUN DMN

^C
@CONTINUE /STAY
@PUSH

 TOPS-20 Command processor 7(7)
@RUN TESTF1

THIS IS A TEST.

CPU time: 0.03  Elapsed time: 0:72
EXIT
@POP
EXIT
```