Running OS Commands and Hot-Swapping Programs

Introduction

Sheerpower's pass statement allows a program to execute external operating system commands. This provides a direct bridge between your application and the host environment, enabling tasks such as invoking utilities, generating files, and integrating with system-level workflows.

Basic Usage

The pass statement accepts a string expression representing a shell command. The command is executed by the operating system. When execution completes, the special variable _integer contains the command's exit status.

pass "exit 9" print 'exit status was '; _integer

This example writes a directory listing to a file named listing.txt.

pass "dir > listing.txt"

Optional NOWAIT Feature

The pass statement supports the nowait modifier.

NOWAIT: Executes the command asynchronously and immediately returns control to the program.

pass nowait: "calc"

This launches the Windows calculator while allowing the current program to continue execution without blocking.

Real-World Example: Exporting Chrome Processes to CSV

This example uses the Windows tasklist utility to retrieve running Chrome processes, writes the results to a CSV file, and loads the data into a Sheerpower cluster.

cluster tasks: image$, pid$, session_name$, session_nbr, memk$ output_file$ = filespec$("@chrome.csv") cmd$ = 'tasklist /fi "imagename eq chrome.exe" /fo csv > ' + output_file$ pass cmd$ cluster input name output_file$, headers 1: tasks print 'Here are the CHROME processes' print cluster tasks: all

Optional NORETURN Feature

The pass statement also supports the noreturn modifier.

NORETURN: Launches a command and then immediately terminates the current Sheerpower program without waiting for the new process to complete.

This is particularly useful for controlled restarts and hot-swap deployments, where a running system transitions to a new version without downtime.

Problem:
Long-running applications may need to update themselves without interrupting service or requiring manual restarts.

Solution:
Use pass noreturn: to launch the updated program instance and immediately exit the current process.

Efficiency:
The existing instance continues operating until the replacement is ready, enabling seamless transition without blocking or resource contention.

Takeaway:
pass noreturn: enables clean, deterministic self-restart behavior for production systems.

!%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% ! c h e c k _ n e w _ c o d e !%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% routine check_new_code: private this_program$, last_datetime$, change_phase$ ask system: program this_program$ select case change_phase$ case '' z0$ = fileinfo$(this_program$, 'revision_date') if last_datetime$ = '' then last_datetime$ = z0$ exit routine end if if last_datetime$ = z0$ then exit routine change_phase$ = 'waiting_for_new_code' case 'waiting_for_new_code' when exception in open file temp_ch: name this_program$, lock close #temp_ch change_phase$ = 'restart' use end when case 'restart' pass noreturn: this_program$ end select end routine

Problem:
File paths for generated output can become inconsistent across environments.

Solution:
Use filespec$("@filename") to anchor output files to the program's execution directory.

Efficiency:
Eliminates hard-coded paths and reduces deployment friction across systems.

Takeaway:
The @ prefix ensures predictable file placement relative to the running program.

Summary:
The pass statement connects Sheerpower programs directly to the operating system. With support for synchronous execution, background processing (nowait), and controlled termination (noreturn), it provides a flexible and powerful mechanism for system integration and deployment workflows.

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