backup-excluded-directories

#!/bin/bash
set -euo pipefail

usage() {
    cat >&2 <<EOM
usage: $0 [OPTIONS...] DIR

Find and list subdirectories under DIR that should be excluded from backup
because they contain TAG_FILE (default .ab-backup-exclude).

Options:

    -h, --help              Print this help message
    -c, --print-contents    Recursively print all paths in excluded directories
    --relative              Print paths sliced relative to DIR
    -t, --tag-file TAG_FILE Use TAG_FILE as name of backup exclude tag file
    -x, --one-file-system   Do not cross filesystem boundaries

EOM
}

relative=
one_file_system=
print_contents=
tag_file=".ab-backup-exclude"

while [ $# -ge 1 ] && [[ $1 == -* ]]; do
    case "$1" in
        -h|--help)
            usage
            exit
            ;;
        -c|--print-contents)
            print_contents=1
            ;;
        --relative)
            relative=1
            ;;
        -t|--tag-file)
            tag_file="$2"
            shift
            ;;
        -x|--one-file-system)
            one_file_system=1
            ;;
        *)
            usage
            echo >&2 "Invalid option: $1"
            exit 1
            ;;
    esac
    shift
done

if [ $# -ne 1 ]; then
    usage
    exit 1
fi

dir=$1

if [ -n "$relative" ]; then
    cd "$dir"
    dir=.
fi

if [ -n "$one_file_system" ]; then
    opts=(-xdev)
else
    opts=()
fi

echo >&2 "Searching $dir for backup exclude tag file $tag_file"

find "$dir" "${opts[@]}" -type f -name "$tag_file" | while read -r file; do
    if [ -n "$print_contents" ]; then
        parent=$(dirname "$file")
        find "$parent" "${opts[@]}"
        continue
    fi
    if [ -n "$relative" ]; then
        file="${file:2}"
    fi
    dirname "$file"
done