Process Module¶

The py.process standard library module provides relational predicates for running shell commands, launching subprocesses, and sleeping. For environment variables and system metadata, see the OS module.

The implementation lives in clausal/modules/py/process.py.

Import¶

-import_from(py.process, [Shell, ShellOutput, ProcessCreate, Sleep])

Or via module import:

-import_module(py.process)
# then use py.process.Shell("ls"), py.process.Sleep(1.0), etc.

Predicates¶

Shell/1¶

Shell(Command) — run a shell command. Succeeds if the exit code is 0, fails otherwise.

run_tests <- Shell("python -m pytest -x")

Shell/2¶

Shell(Command, ExitCode) — run a shell command and unify ExitCode with the integer exit code. Always succeeds (even for non-zero exit codes).

check_status(CMD, CODE) <- Shell(CMD, CODE)

ShellOutput/2¶

ShellOutput(Command, Output) — run a shell command and capture stdout as a string. Fails on non-zero exit code.

git_status(STATUS) <- ShellOutput("git status --porcelain", STATUS)

ShellOutput/3¶

ShellOutput(Command, Output, Error) — run a shell command and capture both stdout and stderr. Fails on non-zero exit code.

compile_and_check(CMD, OUT, ERR) <- ShellOutput(CMD, OUT, ERR)

ProcessCreate/3¶

ProcessCreate(Program, Args, Result) — run a program with an argument list (no shell). Result is a DictTerm with keys exit_code, stdout, stderr.

run_python(CODE, RESULT) <- ProcessCreate("python3", ["-c", CODE], RESULT)

ProcessCreate/4¶

ProcessCreate(Program, Args, Options, Result) — like ProcessCreate/3 with an options DictTerm. Supported options:

Key	Type	Description
`"cwd"`	string	Working directory for the subprocess
`"timeout"`	number	Timeout in seconds (fails on expiry)
`"input"`	string	String to send to stdin
`"env"`	DictTerm	Extra environment variables (merged with current env)

run_in_dir(DIR, RESULT) <- ProcessCreate(
    "python3", ["-c", "import os; print(os.getcwd())"],
    {"cwd": DIR}, RESULT
)

run_with_input(INPUT, RESULT) <- ProcessCreate(
    "cat", [], {"input": INPUT}, RESULT
)

Sleep/1¶

Sleep(Seconds) — pause execution for the given number of seconds (integer or float).

wait_and_retry(GOAL) <- (Sleep(1.0), call(GOAL))

Example¶

-import_from(py.process, [Shell, ShellOutput, ProcessCreate, Sleep])
-import_from(py.json, [Parse, Get])

git_status(STATUS) <- ShellOutput("git status --porcelain", STATUS)

run_tests(RESULT) <- ProcessCreate(
    "python3", ["-m", "pytest", "-x"],
    {"timeout": 60.0}, RESULT
)

poll_until_ready(URL) <- (ShellOutput(f"curl -sf {URL}", _))
poll_until_ready(URL) <- (Sleep(1.0), poll_until_ready(URL))