420chan image downloader

#!/bin/bash
# Dependencies:
#  - curl
#  - jq (for JSON object processing)

if [[ "$1" == "" || "$2" == "" ]] ; then
    echo usage: $0 board_name thread_number
    exit 1
fi

board_name=$1
thread_no=$2
thread_url="https://api.420chan.org/$board_name/res/$thread_no.json"

echo "Downloading thread page at $thread_url"

image_names=$(curl $thread_url \
     | jq '.posts|map(.filename + .ext)' \
     | jq 'map(select(. != null))'  \
     | jq -r 'join("\n")')

image_fmt="https://boards.420chan.org/%s/src/%s"

download_folder="420chan_thread_$thread_no"

test -d $download_folder || mkdir $download_folder

for image_name in $image_names; do
    image_url="$(printf $image_fmt $board_name $image_name)"
    echo "Downloading $image_url..."
    curl "$image_url" > "$download_folder/$image_name" 2>/dev/null
done