shpyx 0.0.21

Run shell commands in Python

shpyx is a simple, lightweight and typed library for running shell commands in Python.

Use shpyx.run to run a shell command in a subprocess:

>>> import shpyx
>>> shpyx.run("echo 1").return_code
0
>>> shpyx.run("echo 1").stdout
'1\n'
>>> shpyx.run("echo 1").stderr
''
>>> shpyx.run("echo 1")
ShellCmdResult(cmd='echo 1', stdout='1\n', stderr='', all_output='1\n', return_code=0)

Installation

Install with pip:

pip install shpyx

How Tos

Run a command

In string format:

>>> shpyx.run("echo 1")
ShellCmdResult(cmd='echo 1', stdout='1\n', stderr='', all_output='1\n', return_code=0)

In list format:

>>> shpyx.run(["echo", ["1"])
ShellCmdResult(cmd='echo 1', stdout='1\n', stderr='', all_output='1\n', return_code=0)

Run a command and print live output

>>> shpyx.run("echo 1", log_output=True)
1
ShellCmdResult(cmd='echo 1', stdout='1\n', stderr='', all_output='1\n', return_code=0)

Run a command with shell specific logic

When the argument to run is a string, an actual shell is created in the subprocess and shell logic can be used. For example, the pipe operator can be used in bash/sh:

>>> shpyx.run("seq 1 5 | grep '2'")
ShellCmdResult(cmd="seq 1 5 | grep '2'", stdout='2\n', stderr='', all_output='2\n', return_code=0)

Create a custom runner

Use a custom runner to override the execution defaults, and not have to pass them to every call.

For example, we can change the default value of log_cmd, so that all commands are logged:

>>> shpyx.run("echo 1")
ShellCmdResult(cmd='echo 1', stdout='1\n', stderr='', all_output='1\n', return_code=0)

>>> shpyx.run("echo 1", log_cmd=True)
Running: echo 1
ShellCmdResult(cmd='echo 1', stdout='1\n', stderr='', all_output='1\n', return_code=0)

>>> runner = shpyx.Runner(log_cmd=True)
>>> runner.run("echo 1")
Running: echo 1
ShellCmdResult(cmd='echo 1', stdout='1\n', stderr='', all_output='1\n', return_code=0)

Propagating terminal control sequences

Note: as of now this is only supported for Unix environments.

Some commands, like psql, might output special characters used for terminal management like cursor movement and colors. For example, the psql command is used to start an interactive shell against a Postgres DB:

shpyx.run(f"psql -h {host} -p {port} -U {user} -d {database}", log_output=True)

However, the above call will not work as good as running psql directly, due to terminal control sequences not being properly propagated. To make it work well, we need to use the script utility which will properly propagate all control sequences:

# Linux:
shpyx.run(f"script -q -c 'psql -h {host} -p {port} -U {user} -d {database}'", log_output=True)
# MacOS:
shpyx.run(f"script -q psql -h {host} -p {port} -U {user} -d {database}", log_output=True)

shpyx provides a keyword argument that does this wrapping automatically, unix_raw:

shpyx.run(f"psql -h {host} -p {port} -U {user} -d {database}", log_output=True, unix_raw=True)

The flag is disabled by default, and should only be used for interactive commands like psql.

API Reference

The following arguments are supported by Runner:

Name	Description	Default
log_cmd	Log the executed command.	False
log_output	Log the live output of the command (while it is being executed).	False
verify_return_code	Raise an exception if the shell return code of the command is not 0.	True
verify_stderr	Raise an exception if anything was written to stderr during the execution.	False
use_signal_names	Log the name of the signal corresponding to a non-zero error code.	True

The following arguments are supported by run:

Name	Description	Default
log_cmd	Log the executed command.	Runner default
log_output	Log the live output of the command (while it is being executed).	Runner default
verify_return_code	Raise an exception if the shell return code of the command is not 0.	Runner default
verify_stderr	Raise an exception if anything was written to stderr during the execution.	Runner default
use_signal_names	Log the name of the signal corresponding to a non-zero error code.	Runner default
env	Environment variables to set during the execution of the command.	Same as parent process
exec_dir	Custom path to execute the command in (defaults to current directory).	Same as parent process
unix_raw	(UNIX ONLY) Whether to use the script Unix utility to run the command.	False

Implementation details

shpyx is a wrapper around the excellent subprocess module, aiming to concentrate all the different API functions (Popen/communicate/poll/wait) into a single function - shpyx.run.

While the core API logic is fully supported on both Unix and Windows systems, there is some OS specific code for minor quality-of-life improvements. For example, on non Windows systems, fcntl is used to configure the subprocess to always be incorruptible (which means one can CTRL-C out of any command).

Security

The call to subprocess.Popen uses shell=True when the input to run is a string (to support shell logic like bash piping). This means that an actual system shell is being created, and the subprocess has the permissions of the main Python process.

It is therefore recommended not pass any untrusted input to shpyx.run.

For more info, see security considerations.

Useful links

Relevant Python libraries:

• subprocess
• shlex

Other user libraries for running shell commands in Python:

• sarge
• sh

Contributing

To contribute simply open a PR with your changes.

Tests, linters and type checks are run in CI through GitHub Actions.

Running checks locally

To run checks locally, start by installing all the development dependencies:

poetry install

To run the linters use pre-commit:

pre-commit run -a

To run the unit tests use pytest:

pytest -c tests/pytest.ini tests

To run type checks use mypy:

mypy --config-file shpyx/mypy.ini shpyx tests

To trigger a deployment of a new version upon merge, bump the version number in pyproject.toml.