Dockerfile FROM Instruction Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching dockerfile from instruction, ported and verified for Python. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# Dockerfile FROM Instruction
# ReDoS-safe | RegexVault — Dev & Systems > Docker

import re

dockerfile_from_instruction_pattern = re.compile(r'^FROM\s+(?:--platform=[^\s]+\s+)?([a-z][a-z0-9\-._/]*(?::[a-zA-Z0-9._\-]+|@sha256:[a-fA-F0-9]{64})?)(?:\s+AS\s+([a-zA-Z][a-zA-Z0-9_\-]*))?$')

def validate_dockerfile_from_instruction(value: str) -> bool:
    return bool(dockerfile_from_instruction_pattern.fullmatch(value))

# Example
print(validate_dockerfile_from_instruction("FROM nginx"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Docker category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Group 1 = image reference, group 2 = AS alias. Multi-stage builds use FROM...AS extensively. 'scratch' is a special minimal base image. --platform enables cross-platform builds.