How to Add a Dry Run Flag to a Python CLI Command

Build a Python CLI command with a --dry-run flag that previews actions and exits before making real changes.

Easy Python 3.9+ Aug 9, 2026 Functions & basics 12 views 0 copies

argparse cli dry-run command-line scripting

Python code

22 lines

Python 3.9+

import argparse
import sys

def main():
    parser = argparse.ArgumentParser(description="Sample CLI command with dry-run flag")
    parser.add_argument("--name", required=True, help="Name to greet")
    parser.add_argument("--dry-run", action="store_true", dest="dry_run",
                        help="Show what would be done without executing")
    args = parser.parse_args()

    greeting = f"Hello, {args.name}!"

    if args.dry_run:
        print(f"[DRY RUN] Would output: {greeting}")
        print("[DRY RUN] Skipping actual execution")
        return

    print(greeting)
    print("Actual execution completed")

if __name__ == "__main__":
    main()

Output

stdout

Without flag:
$ python script.py --name Ada
Hello, Ada!
Actual execution completed

With dry run:
$ python script.py --name Ada --dry-run
[DRY RUN] Would output: Hello, Ada!
[DRY RUN] Skipping actual execution

How it works

The --dry-run flag uses store_true, which sets args.dry_run to True when present and False otherwise. The code then prints what would happen and calls return early to skip the real execution path. Using dest gives parser.add_argument('--dry-run') a Python-friendly attribute name without hyphens.

Common mistakes

Returning without printing the expected output in dry-run mode
Using a positional `--dry-run` value (like a string) instead of `action='store_true'`

Variations

Add `--force` or `--yes` to override the dry-run guard when needed
Extend with `argparse.BooleanOptionalAction` in Python 3.9+ for automatic `--no-dry-run`

Real-world use cases

Preview destructive database migrations or schema changes before running them in production.
Dry-run a deployment script to validate config and targets without touching live servers.
Stage batch file-reorganization scripts and confirm the file mapping before moving data.

How to Add a Dry Run Flag to a Python CLI Command

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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