Shell script to split .djvu files into pages, one per file

djvusplit.sh

#!/bin/bash
# dlitz 2022
# SPDX-License-Identifier: CC0-1.0

set -eu

usage() {
    echo "usage: $0 [-v] inputfile.djvu output-dir"
    echo "Split a DjVu document into multiple pages, one per file."
    echo "Use djvm -c to reassemble the file."
    echo ""
    echo "Example: $0 foo.djvu pages"
}
if [ "$*" = "--help" ]; then
    usage
    exit 0
elif [ "${1-}" = "-v" ]; then
    verbose=-v
    shift 1
else
    verbose=
fi
if [ "$#" -ne 2 ]; then
    usage >&2
    exit 2
fi
input_file="$(readlink -f "$1")"        # absolute path
output_dir="$2"
page_count=$( djvused "$input_file" -e n )

if ! test -d "$output_dir"; then
    mkdir "$output_dir"
elif [ "$(find "$output_dir" -mindepth 1 -maxdepth 1 | wc -l)" -gt 0 ]; then
    echo >&2 "$0: error: directory already exists and is not empty: $output_dir"
    exit 1
fi

cd "$output_dir"

generate_script() {
    for page_num in $( seq 1 "$page_count" ); do
        output_file=$( printf "page-%04d.djvu" "$page_num" )
        echo "select $page_num; save-page-with $output_file;"
    done
}

if [ "${verbose:+1}" ]; then
    # show the script being used
    generate_script
fi

generate_script | djvused ${verbose} "$input_file"