Script to update image embed links in Markdown files

I'm preparing to migrate this blog thingy from Hashnode (which has been great!) to a GitHub Pages site with Jekyll [1] so that I can write posts locally and then just do a `git push` to publish them - and get some more practice using `git` in the process. Of course, I've written some admittedly-great content here and I don't want to abandon that.

[1] GitHub Pages site with Jekyll

Hashnode helpfully automatically backs up my posts in Markdown format to a private GitHub repo so it was easy to clone those into a local working directory, but all the embedded images were still hosted on Hashnode:

=> https://cdn.hashnode.com/res/hashnode/image/upload/v1600098180227/lhTnVwCO3.png Image: Clever image title

I wanted to download those images to `./assets/images/posts-2020/` within my local Jekyll working directory, and then update the `*.md` files to reflect the correct local path... without doing it all manually. It took a bit of trial and error to get the regex working just right (and the result is neither pretty nor elegant), but here's what I came up with:

#!/bin/bash
# Hasty script to process a blog post markdown file, capture the URL for embedded images,
# download the image locally, and modify the markdown file with the relative image path.
#
# Run it from the top level of a Jekyll blog directory for best results, and pass the
# filename of the blog post you'd like to process.
#
# Ex: ./imageMigration.sh 2021-07-19-Bulk-migrating-images-in-a-blog-post.md
postfile="_posts/$1"
imageUrls=($(grep -o -P '(?<=!\[)(?:]+)\]\((+)' $postfile | grep -o -P 'http.*'))
imageNames=($(for name in ${imageUrls[@]}; do echo $name | grep -o -P '+\.[[:alnum:]]+$'; done))
imagePaths=($(for name in ${imageNames[@]}; do echo "assets/images/posts-2020/${name}"; done))
echo -e "\nProcessing $postfile...\n"
for index in ${!imageUrls[@]}; do
    echo -e "${imageUrls[index]}\n => ${imagePaths[index]}"
    curl ${imageUrls[index]} --output ${imagePaths[index]}
    sed -i "s|${imageUrls[index]}|${imagePaths[index]}|" $postfile
done

I could then run that against all of the Markdown posts under `./_posts/` with:

for post in $(ls _posts/); do ~/scripts/imageMigration.sh $post; done

And the image embeds in the local copy of my posts now all look like this:

=> lhTnVwCO3.png Image: Clever image title

Brilliant!

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Script to update image embed links in Markdown files

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