Split ~/.ssh/config file into separate per-host files

ssh_config_split.py

#!/usr/bin/env python
import os
import shutil
import re
import sys
import difflib
import argparse


def parse_ssh_config(config_path):
    with open(config_path, "r") as f:
        config_lines = f.readlines()

    hosts = {}
    host_lines = []
    host_name = None

    for line in config_lines:
        if re.match(r"^Host\b", line):
            if host_lines and host_name is not None:
                hosts[host_name] = host_lines
            host_name = re.search(r"^Host\s+(.+)", line).group(1)
            host_lines = []
        host_lines.append(line)

    if host_lines and host_name is not None:
        hosts[host_name] = host_lines

    return hosts


def backup_ssh_config(ssh_config_path, ssh_config_backup_base):
    backup_index = 0
    ssh_config_backup_path = ssh_config_backup_base
    while os.path.exists(ssh_config_backup_path):
        backup_index += 1
        ssh_config_backup_path = f"{ssh_config_backup_base}.{backup_index}"

    shutil.copy2(ssh_config_path, ssh_config_backup_path)
    return ssh_config_backup_path


def split_ssh_config(force=False):
    ssh_config_path = os.path.expanduser("~/.ssh/config")
    ssh_config_backup_base = os.path.expanduser("~/.ssh/config.backup")
    ssh_config_d_path = os.path.expanduser("~/.ssh/config.d")

    # Make a backup of the original config file
    backup_ssh_config(ssh_config_path, ssh_config_backup_base)

    # Create the config.d directory if it doesn't exist
    if not os.path.exists(ssh_config_d_path):
        os.makedirs(ssh_config_d_path)

    # Parse the config file and get host configurations
    hosts = parse_ssh_config(ssh_config_path)

    # Write each host configuration to a separate file in config.d directory
    for host_name, host_lines in hosts.items():
        # Replace any non-filename friendly characters
        safe_host_name = re.sub(r"[^\w\-_]", "_", host_name)
        host_config_file = os.path.join(ssh_config_d_path, f"{safe_host_name}.conf")

        if os.path.exists(host_config_file):
            with open(host_config_file, "r") as f:
                existing_lines = f.readlines()

            if existing_lines != host_lines:
                if force:
                    sys.stderr.write(f"Warning: Overwriting {host_config_file}\n")
                else:
                    sys.stderr.write(
                        f"Error: {host_config_file} already exists and has different content.\n"
                    )
                    diff = difflib.unified_diff(
                        existing_lines,
                        host_lines,
                        fromfile=host_config_file,
                        tofile=f"{safe_host_name}_new.conf",
                    )
                    sys.stderr.writelines(diff)
                    sys.stderr.write("\n")
                    continue

        with open(host_config_file, "w") as f:
            f.writelines(host_lines)

    # Replace the original config file with an include directive and a comment
    with open(ssh_config_path, "w") as f:
        f.write(
            "# This file is generated by ssh_config_split - see ~/.ssh/config.d for host configurations.\n"
        )
        f.write(f"Include {ssh_config_d_path}/*\n")


if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        description="Splits your ~/.ssh/config file into separate per-host files in ~/.ssh/config.d/"
    )
    parser.add_argument(
        "--force",
        action="store_true",
        help="Force overwriting existing host config files in ~/.ssh/config.d/",
    )
    args = parser.parse_args()

    split_ssh_config(force=args.force)