About a year ago, Github launched a feature that allows adding of README to a user profile. To add the README to your profile, you have to: create a repository with a name your Github username public matching place the in the of the repository README.md root You can learn more about it in . Github documentation What is a Dynamic Github Profile? The dynamic Github profile is updated automatically on some external event or by schedule. It is possible with the use of . Github Actions are another recently released Github feature. Github Actions is essentially a CI/CD system that allows creating and running of custom workflows. Github Actions I first learned about the profile README in on Hackernoon. The guy used PHP to fetch and update a list of the latest posts in his blog. Although I am a PHP expert, I desired to make it more challenging. I realized that XML parsing and replacing text in a file is achievable using Bash native tools only. this article Parsing RSS feed RSS feed is a plain XML file with a simple schema. Here’s a sample from my freshly launched blog: <?xml version="1.0" encoding="utf-8" standalone="yes"?>
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:content="http://purl.org/rss/1.0/modules/content/">
  <channel>
    <title>Posts on Aleksandr Tabakov&#39;s technical blog | atabakoff</title>
    <link>https://atabakoff.com/posts/</link>
    <description>Recent content in Posts on Aleksandr Tabakov&#39;s technical blog | atabakoff</description>
    <image>
      <url>https://atabakoff.com/aleksandr_tabakov.jpeg</url>
      <link>https://atabakoff.com/aleksandr_tabakov.jpeg</link>
    </image>
    <generator>Hugo -- gohugo.io</generator>
    <lastBuildDate>Fri, 27 May 2022 21:33:51 +0200</lastBuildDate><atom:link href="https://atabakoff.com/posts/index.xml" rel="self" type="application/rss+xml" />
    <item>
      <title>How to run Vaultwarden in Docker/Podman as a systemd service</title>
      <link>https://atabakoff.com/how-to-run-vaultwarden-in-podman-as-a-systemd-service/</link>
      <pubDate>Fri, 27 May 2022 21:33:51 +0200</pubDate>
      
      <guid>https://atabakoff.com/how-to-run-vaultwarden-in-podman-as-a-systemd-service/</guid>
      <description>Running Vaultwarden in a container as a systemd service using Podman. How to install Podman, run Vaultwarden in a container, create a systemd config for Vaultwarden service and manage it using systemctl.</description>
    </item>
    
  </channel>
</rss> Each post is represented by an element where we need , , and . item title link pubDate Parsing RSS feed with grep The naive approach is to use and then build markdown in a bash loop. Let’s first try to : grep grep wget --quiet -O rss.xml https://atabakoff.com/posts/index.xml
cat rss.xml | grep -Po '<(title|link|pubDate)>[^<]+'
<title>Posts on Aleksandr Tabakov&#39;s technical blog | atabakoff
<link>https://atabakoff.com/posts/
<link>https://atabakoff.com/aleksandr_tabakov.jpeg
<title>How to run Vaultwarden in Docker/Podman as a systemd service
<link>https://atabakoff.com/how-to-run-vaultwarden-in-podman-as-a-systemd-service/
<pubDate>Fri, 27 May 2022 21:33:51 +0200 Not bad, but we need to get rid of the first three lines and the opening tag: cat rss.xml | grep -Po '<(title|link|pubDate)>[^<]+' | tail -n +4 \
     | grep -oE '>([^>]+)' | grep -oE '([^>]+)'
How to run Vaultwarden in Docker/Podman as a systemd service
https://atabakoff.com/how-to-run-vaultwarden-in-podman-as-a-systemd-service/
Fri, 27 May 2022 21:33:51 +0200
Just to test grep
https://atabakoff.com/testing-grep/
Fri, 31 May 2022 18:33:51 +0200 I added one extra item to test if my expression works with multiple posts. At this point, I start thinking that might not be the best option. I quickly wrote a converter to convert RSS to markdown, before researching other options: grep #!/bin/bash

items=$( cat rss.xml | grep -Po '<(title|link|pubDate)>[^<]+' | tail -n +4 \
    | grep -oE '>([^>]+)' | grep -oE '([^>]+)' )

IFS=$'\n'
count=0
for item in $items
do
   case $(expr $count % 3) in
    '0')
        title=$item
        link=''
        pubDate=''
        ;;
    '1')
        link=$item
        ;;
    '2')
        pubDate=$( date -d "$item" +'%d/%m/%Y' )
        cat<<EOF
* $pubDate [$title]($link)
EOF
        ;;
    esac
    count=$(($count + 1))
done Run it to validate: ./test.sh
* 27/05/2022 [How to run Vaultwarden in Docker/Podman as a systemd service](https://atabakoff.com/how-to-run-vaultwarden-in-podman-as-a-systemd-service/)
* 31/05/2022 [Just to test grep](https://atabakoff.com/testing-grep/) Testing performance My RSS feed is tiny. To measure performance, we need to run the parser many times. I created a file: test.sh #!/bin/bash

x=100

while [ "$x" -gt "0" ] ; do
   $(/bin/bash $1) 2>/dev/null
   x=$((x-1))
done It accepts a script file as a parameter and runs it 100 times in a loop. Let’s run it with to see how much it’s taking to parse the feed: time > time ./test.sh grep-rss.sh 
./test.sh grep.sh  1,87s user 0,72s system 137% cpu 1,883 total Not very impressive but expected due to the use of regular expressions. Parsing RSS feed in Bash I started googling if there’s a way to parse XML in Bash and found this . It describes the same problem of parsing the RSS feed. I modified the code for my needs and stored it in the file: awesome solution parse-rss.sh #!/bin/bash

xmlgetnext () {
   local IFS='>'
   read -d '<' TAG VALUE
}

cat $1 | while xmlgetnext ; do
   case $TAG in
      'item')
         title=''
         link=''
         pubDate=''
         ;;
      'title')
         title=$VALUE
         ;;
      'link')
         link=$VALUE
         ;;
      'pubDate')
         pubDate=$( date -d "$VALUE" +'%d/%m/%Y' )
         ;;
      '/item')
         cat<<EOF
* $pubDate [$title]($link)
EOF
         ;;
   esac
done I ran the same test to compare performance: time ./test.sh parse-rss.sh
./test.sh parse.sh  0,81s user 0,33s system 109% cpu 1,042 total Almost faster: vs . It is the final approach I chose for processing of RSS feed. two times 1,042 1,883 Updating README.md Updating a list of posts is simply a replacement. Since markdown allows the usage of HTML code, we can use HTML comments to mark a placeholder for posts: 
 The standard tool to replace text in Bash is but it has one limitation. It is a string editor, only processing one string in one step. In our case, both the placeholder and the posts list is a multiline text. Here’s how I solved it: sed #!/bin/bash

NUM=$(($2*3))

POSTS=$( cat $1 | head $NUM | tr '\n' '\t' )
cat README.md | tr '\n' '\t' \
    | sed -E "s#(<\!--blog:start-->).*(<\!--blog:end-->)#\1\t${POSTS}\2#g" \
    | tr '\t' '\n' > README.tmp
mv README.tmp README.md
rm -f rss.xml posts.md Some things worth explaining: is the number of lines for the specified number of posts; in my case, I want to show five posts taking three lines each (title, link, date) NUM=$(($2*3)) is to convert the text to a single line to process it by tr '\n' '\t' sed is to bring back newlines tr '\t' '\n' Github Actions Pipeline Now we have our scripts, and we need to put them into a pipeline. Github Actions are looking at a special directory and process each file there. I’ve created a file there with the following content: .gihub/workflows .yaml posts.yml name: Update blog posts

on:
  push:
  workflow_dispatch:
  schedule:
    - cron:  '0 0 * * *'

jobs:
  update-readme-with-latest-posts:
    runs-on: ubuntu-latest
    steps:
    - name: Clone repository
      uses: actions/checkout@v2
      with:
        fetch-depth: 1
    - name: Fetch RSS feed
      run: wget --quiet -O rss.xml https://atabakoff.com/posts/index.xml
    - name: Parse RSS feed
      run: |
        cd ${GITHUB_WORKSPACE}
        ./src/parse-rss.sh rss.xml > posts.md        
    - name: Update README.md
      run:  |
        cd ${GITHUB_WORKSPACE}
        ./src/update-readme.sh posts.md 5        
    - name: Push changes
      run: |
        git config --global user.name "${GITHUB_ACTOR}"
        git config --global user.email "${GITHUB_ACTOR}@users.noreply.github.com"
        git commit -am "Updated blog posts" | exit 0
        git push Here’s what needs to be explained: is to run it on push push is a schedule, in my case every day at midnight cron: '0 0 * * *' clones a repository uses: actions/checkout@v2 Then I split fetching, parsing, and updating into separate steps. It allows me quickly localize a problem if something goes wrong. Something worth noting: is to move to the current working directory, which is the newly cloned repository cd ${GITHUB_WORKSPACE} is your username ${GITHUB_ACTOR} is a special Github email one can use to push the changes to the repository ${GITHUB_ACTOR}@users.noreply.github.com Conclusion You can find the full solution in . It’s been a lot of fun solving this problem with pure Bash. my profile repository That being said, there’re lots of community-made Github actions. They allow creating a dynamic profile without writing any code. All you need to do is to write some YAML. But there’s little challenge in that. It is not a warrior way. Also published . here

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