Download all files from a Slack workspace export folder.

slack-files-downloader.sh

#!/bin/bash 
#
# This script will browse a Slack export folder and download all files in a new /export folder
# 
# HOW TO:
# 1. As a Workspace admin, download an export of your Slack history (https://www.slack.com/services/export) 
# 2. Make sure you have jq installed (https://stedolan.github.io/jq/)
# 3. Place this file at the root of your Slack export folder, next to channels.json
# 4. Run `bash slack-files-downloader.sh` in your terminal
#
# OPTIONS
# -o Overwrite files if they already exist in destination folder, otherwise skip them.
# -s Do not show message when a file is skipped
# -l Store links to external files into an html file at expected path
# -v Verbose logging of file paths


loglevel=0
while getopts "oslv" flag
do
    case $flag in
        o) overwrite=true;;
        s) silent=true;;
        l) link_external=true;;
        v) loglevel=$((loglevel+1));;
    esac
done

printf "\nSelect one specific file type to download or leave empty for any (e.g. mp3, binary, jpg, png):\n"
read usertype

printf "\nSelect a channel to look into or leave empty for all channels:\n"
read userchannel

printf "\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\nExporting channels\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n"

if [[ -z $userchannel ]]
then
	export_channels=$(cat channels.json | jq -rc '.[].name')
else
	export_channels=$userchannel
fi

for channel in $export_channels
do
	if [[ -d "$channel" ]]
	then
		printf "\n============================================\nLooking into #$channel...\n============================================\n"

		for file in "$channel"/*.json
		do
			(( $loglevel >= 1 )) && printf "Checking channel file '$file'\n"
			
			for a in $(cat $file | jq -c '.[].files[]? | [.file_access, .name, .is_external, .filetype, .timestamp, .url_private_download, .external_url, .url_private] | del(..|nulls)' | sed 's/ //g')
			do
				filetype=$(echo $a | jq -r '.[3]')

				if [[ $filetype == $usertype ]] || [[ -z $usertype ]] || [[ -z $filetype ]]
				then
					file_access=$(echo $a | jq -r '.[0]')
					if [[ $file_access == "not_visible" ]]
					then
						(( $loglevel >= 1 )) && printf "Skipping non visible file '$filename_raw': $a\n"
						continue
					fi
					
					filename_raw=$(echo $a | jq -r '.[1]')
					if [[ ! -z $filename_raw  ]] && [[ $filename_raw != "null"  ]] 
					then		
						
						(( $loglevel >= 2 )) && printf "Checking file '$filename_raw': $a\n"

						filename=$(echo $filename_raw | sed -e 'y/āáǎàçēéěèīíǐìōóǒòūúǔùǖǘǚǜüĀÁǍÀĒÉĚÈĪÍǏÌŌÓǑÒŪÚǓÙǕǗǙǛÜ:/aaaaceeeeiiiioooouuuuuuuuuAAAAEEEEIIIIOOOOUUUUUUUUU_/')
						filename="${filename##*/}"
						
						ts=$(echo $a | jq -r '.[4]')
						year=$(date -r $ts '+%Y')
						month=$(date -r $ts '+%m')

						# prefix filenames with date/time, as the same filename could be used
						# multiple times in different slack messages with different file contents.
						datetime=$(date -r $ts '+%Y%m%d-%H%M%S')
						filename="${datetime}-${filename}"
						
						base_folder="EXPORT/$channel/$year/$month"
						file_path="$base_folder/$filename"
						if [ -f "$file_path" ] && [[ $overwrite != true ]]
						then
							if [ ! -s "$file_path" ]
							then
								printf "$file_path exists, but file is empty. Retrying!\n"
								rm "$file_path"
							else
								if [[ $silent != true ]]
								then
									printf "$file_path already exists in destination folder. Skipping!\n"
								fi
								continue
							fi
						fi
						
						is_external=$(echo $a | jq -r '.[2]')
						url=$(echo $a | jq -rc '.[5]')
						
						if [[ $is_external == "true" ]]
						then
							if [ ! -f "${file_path%.*}".* ]
							then
								if [[ $link_external == "true" ]]
								then
									file_path_link="${file_path%.*}.html"
									echo "download external file at <a href=\"$url\">$url</a> to <tt>$file_path</tt>" > "$file_path_link"
									echo "Stored link to external file as link in '$file_path_link'"
								else
									echo "download external file at '$url' manually to '$file_path'"
								fi
							fi
							continue
						fi
						
						mkdir -p "$base_folder"
						
						printf "downloading to $file_path with $ts\n"            
						curl --progress-bar $url -o "$file_path"
					fi
				fi
			done
		done
	fi
done


if [[ ! -z $userchannel ]]
then
	exit 0
fi

printf "\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\nExporting canvases\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n"

root_folder_canvases="export/CANVAS"
for canvas in $(cat canvases.json | jq -c '.[] | [.name, .id, .filetype, .created, .url_private_download]')
do
	filetype=$(echo $canvas | jq -r '.[2]')
	if [[ $filetype != $usertype ]] && [[ ! -z $usertype ]] && [[ ! -z $filetype ]]
	then
		continue
	fi
	
	filename_raw=$(echo $canvas | jq -r '.[0]')
	canvas_id=$(echo $canvas | jq -r '.[1]')
	
	ts=$(echo $canvas | jq -r '.[3]')
	year=$(date -r $ts '+%Y')
	month=$(date -r $ts '+%m')
	datetime=$(date -r $ts '+%Y%m%d-%H%M%S')
	
	filename="${datetime}_${canvas_id}-${filename_raw}"
	file_path="$root_folder_canvases/$filename"
	
	if [ -f "$file_path" ] && [[ $overwrite != true ]]
	then
		if [[ $silent != true ]]
		then
			printf "$filename already exists in destination folder. Skipping!\n"
		fi
		continue
	fi
	
	mkdir -p "$root_folder_canvases"
	url=$(echo $canvas | jq -rc '.[4]')
	
	printf "downloading to $file_path with $ts\n"
	curl --progress-bar "$url" -o "$file_path"
	
done


printf "\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\nExporting avatars\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n"

root_folder_users="export/USER"
IFS=$'\n'
for user in $(cat users.json | jq -c '.[] | [.name, .profile]')
do
	user_name=$(echo $user | jq -r '.[0]')
	profile=$(echo $user | jq -rc '.[1]')
	
	root_folder_user="$root_folder_users/$user_name"
	mkdir -p "$root_folder_user"
	
	for image in $(echo $profile | jq -rc 'to_entries[] | select(.key | startswith("image")) | select(.value != "") | [.key, .value]')
	do
		image_name=$(echo $image | jq -rc '.[0]')
		image_path="$root_folder_user/$image_name.png"
		if [ -f "$image_path" ] && [[ $overwrite != true ]]
		then
			if [[ $silent != true ]]
			then
				printf "$image_path already exists in destination folder. Skipping!\n"
			fi
			continue
		fi
		
		image_url=$(echo $image | jq -rc '.[1]')
		echo "Downloading $user_name/$image_name: $image_url"
		curl --progress-bar "$image_url" -o "$image_path"
	done
done

Cheers, glad my contribution helped someone else! Thanks for your addition of appending the extension where applicable. I'll merge that in, should I ever need to run the script again.