Command-Line Flag (Short / Long) Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching command-line flag (short / long), 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

# Command-Line Flag (Short / Long)
# ReDoS-safe | RegexVault — Dev & Systems > Shell

import re

commandline_flag_short_long_pattern = re.compile(r'^(?:--([a-zA-Z][a-zA-Z0-9\-]{0,49})(?:=(.+))?|-([a-zA-Z0-9])(.*))$')

def validate_commandline_flag_short_long(value: str) -> bool:
    return bool(commandline_flag_short_long_pattern.fullmatch(value))

# Example
print(validate_commandline_flag_short_long("--verbose"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Shell 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

Short flags: group 3=char, group 4=combined value (e.g., -ofile.txt). Long flags: group 1=name, group 2=value after =. GNU getopt allows both --flag value and --flag=value.