shellsafe

Run shell commands safely using Python 3.14 template strings. Values can never turn into commands.

from shellsafe import run

message = get_user_input()          # "fix; rm -rf ~"
run(t"git commit -m {message}")
# argv: ["git", "commit", "-m", "fix; rm -rf ~"]
# one command; the scary text is just an argument

Why this package exists

Python 3.14 added template strings (PEP 750). Now Python keeps your fixed text and your values separate at the language level.

Shell commands are the first place people want to use this. That is because f-strings inside shell commands have caused real security bugs for ten years:

subprocess.run(f"git commit -m {message}", shell=True)
# if message = "fix; rm -rf ~"  ->  two commands run. The second one is bad.

Python planned to solve this officially (PEP 787), but that plan was postponed. So today there is no standard way to run shell commands safely with templates. This package fills that gap.

Install

pip install shellsafe

Needs Python 3.14 or newer.

How to use

Run a command. Your values always stay one argument each:

from shellsafe import run

run(t"mkdir {path}")
run(t"docker build -t {tag} .", check=True, timeout=300)

Get the output as text:

from shellsafe import capture

res = capture(t"grep {pattern} {file}")
print(res.stdout, res.returncode)

Need pipes? Works on Linux and macOS. Your values are quoted safely first:

from shellsafe import shx

shx(t"cat {file} | wc -l")

Want to see exactly what will run?

from shellsafe import plan

print(plan(t"git commit -m {message}"))
# argv: ["git","commit","-m","fix; rm -rf ~"]

Safety rules

Case What happens
Any value you pass becomes one argument, exactly as given
Value used as the program name error: program names must be written as fixed text
Shell features on Windows error: we cannot make Windows safe this way, so we say no
RAW() misuse error: one value only, used as-is, no nesting

RAW(...) marks content you have already made safe by hand. It is loud and easy to find in code review, so trust is never hidden.

Limits

  • Shell features (pipes, redirections) work on Linux and macOS only. Windows supports plain commands only.
  • run() refuses templates that contain shell metacharacters. Use shx() for those.
  • Byte values are rejected. Decode them first.
  • We keep your command safe to build and run. Testing what your command does is still your job.

Needs

  • Python 3.14 or newer
  • Linux, macOS, Windows (pipes work on Linux and macOS only)

More

License: MIT

Project links

Data verified by PyPI on Aug 27, 2026
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Key dates

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  • Released:
Newer release available (0.3.2)

1 maintainer

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Credits

Author: Rahul Sharma

GitHub Statistics

Data verified by PyPI on Aug 27, 2026
The GitHub source repository was provided by the project maintainers and verified by PyPI at the time of upload. Stars, forks, and open issues/PRs are derived from that repository and have not been independently verified.

License expression

MIT
View SPDX License List

Requires

Python >=3.14

Tags

automation command-injection injection pep750 security shell subprocess t-strings template-strings

Classifiers

Report project as malware

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