Sync repos between devices using bash

Sometimes it’s helpful to sync a Git repository directly from one machine to another without using a Git host like GitHub. If you can SSH into the machine(s) involved, you can use Bash’s rsync command. Rsync’s defaults aren’t great for syncing repos for several reasons, but a Bash script can fix that.

I named the script ,sync-repo:

,sync-repo . staging:/home/chris/repos/url-shortener

This syncs the current directory (.) to /home/chris/repos/url-shortener in a machine named staging as defined in an SSH config file. The first argument is the source, and the second is the destination. Files and folders ignored by Git are not copied. This command can also be used to make a local copy of a local repo by not specifying any remote host.

Here’s the contents of my ,sync-repo file:

#!/usr/bin/env bash
set -euo pipefail

# Syncs a git repo either locally or to/from another machine. Files and
# folders ignored by git are not copied.
# https://chriswheeler.dev/posts/copy-repos-between-devices-using-bash/

if [ $# -ne 2 ]; then
    echo "Usage: $0 <source_repo> <destination>" >&2
    exit 1
fi

SRC="$1"
DEST="$2"

if [ -z "$SRC" ]; then
    echo 'Error: source cannot be empty' >&2
    exit 1
elif [ -z "$DEST" ]; then
    echo 'Error: destination cannot be empty' >&2
    exit 1
fi

# try to make sure the destination is not a root folder or a home folder
if [[ "$DEST" =~ \.\. ]]; then
    echo 'Error: destination cannot contain ".."' >&2
    exit 1
fi
if [[ "$DEST" =~ ^([^:]+):(.*)$ ]]; then
    # DEST is remote
    DEST_PATH="${BASH_REMATCH[2]}"
else
    # DEST is local
    DEST_PATH="$DEST"
fi
if [ -z "$DEST_PATH" ]; then
    echo 'Error: destination path cannot be empty' >&2
    exit 1
elif [[ "$DEST_PATH" =~ ^/+\.?/*$ ]]; then
    echo 'Error: destination path cannot be a root folder' >&2
    exit 1
elif [[ "$DEST_PATH" =~ ^~/*$ || "$DEST_PATH" =~ ^/(home|Users)/[^/]+/*$ ]]; then
    echo 'Error: destination path cannot be a home folder' >&2
    exit 1
elif [[ "$DEST" == "$DEST_PATH" && "$DEST_PATH" != /* ]]; then
    # DEST is local and DEST_PATH is relative
    CURRENT_DIR="$(pwd)"
    if [[ "$CURRENT_DIR" == '/' ]]; then
        echo 'Error: destination path cannot be relative to the root folder' >&2
        exit 1
    elif [[ "$DEST_PATH" =~ ^\./*$ && "$CURRENT_DIR" =~ ^/(home|Users)/[^/]+$ ]]; then
        echo 'Error: destination path cannot be a home folder' >&2
        exit 1
    fi
fi

# get a list of files and folders ignored by git
EXCLUDES_FILE="$(mktemp)"
trap 'rm -f $EXCLUDES_FILE' EXIT
if [[ "$SRC" =~ ^([^:]+):(.+)$ ]]; then
    # SRC is remote
    HOST="${BASH_REMATCH[1]}"
    REMOTE_PATH="${BASH_REMATCH[2]}"
    # shellcheck disable=SC2029
    ssh "$HOST" "cd \"$REMOTE_PATH\" && git ls-files --exclude-standard --others --ignored --directory" > "$EXCLUDES_FILE"
else
    # SRC is local
    (cd "$SRC" && git ls-files --exclude-standard --others --ignored --directory) > "$EXCLUDES_FILE"
fi

rsync --recursive --compress --rsh=ssh --perms --times --group \
    --exclude-from="$EXCLUDES_FILE" \
    "$SRC" "$DEST"

I learned a lot of how to write this by combining a few answers in this StackOverflow discussion.

--recursive recursively syncs all directories
--compress compresses the data before sending, making the transfer significantly faster
--rsh=ssh tells rsync to make the connection over SSH to ensure encryption
--perms preserves permissions
--times preserves modification times
--group preserves group
--exclude-from makes rsync ignore files & folders listed in a file

git ls-files --exclude-standard --others --ignored --directory lists all files and folders in the repo that are being ignored by Git.

I chose to start the ,sync-repo command’s name with a comma because that makes it much less likely to conflict with future commands as explained in Start all of your commands with a comma.