command line on foosel.nethttps://foosel.net/tags/command-line/Recent content in command line on foosel.netHugoen-usGina Häußge (foosel)Tue, 12 Mar 2024 00:00:00 +0000How to quickly create a header modifying reverse proxy with mitmproxyhttps://foosel.net/til/2024-03-12-how-to-quickly-create-a-header-modifying-reverse-proxy-with-mitmproxy/Tue, 12 Mar 2024 00:00:00 +0000https://foosel.net/til/2024-03-12-how-to-quickly-create-a-header-modifying-reverse-proxy-with-mitmproxy/<p>I&rsquo;m currently in the process of testing some changes on OctoPrint involving its automatic user login via request headers, and for that needed to quickly set up a reverse proxy that would modify the headers of the requests going to the development server for some quick testing.</p> <p>Specifically, I wanted a quick CLI tool that would allow me to set up a reverse proxy listening on port 5555, forwarding to <code>http://localhost:5000</code> while also setting the headers <code>X-Remote-User</code> to <code>remote</code> and <code>X-Remote-Host</code> to <code>localhost:5555</code>.</p>I’m currently in the process of testing some changes on OctoPrint involving its automatic user login via request headers, and for that needed to quickly set up a reverse proxy that would modify the headers of the requests going to the development server for some quick testing.

Specifically, I wanted a quick CLI tool that would allow me to set up a reverse proxy listening on port 5555, forwarding to http://localhost:5000 while also setting the headers X-Remote-User to remote and X-Remote-Host to localhost:5555.

Enter mitmproxy, or more specifically its mitmdump tool, which turned out to be a great tool for this job.

All I needed was to run the following command:

mitmdump --mode reverse:http://localhost:5000@5555 --modify-headers "/X-Remote-User/remote" --modify-headers "/X-Forwarded-Host/localhost:5555"

This does the following:

  • --mode reverse:http://localhost:5000@5555 sets up a reverse proxy listening on port 5555, forwarding to http://localhost:5000
  • --modify-headers "/X-Remote-User/remote" sets the X-Remote-User header to remote
  • --modify-headers "/X-Forwarded-Host/localhost:5555" sets the X-Forwarded-Host header to localhost:5555

With that the reverse proxy test page in OctoPrint turned all green and I could test my changes without having to set up an actual reverse proxy in front of the development server.

]]>How to print Deutsche Post stamps via the command line on a Brother QL label printerhttps://foosel.net/til/2024-01-11-how-to-print-deutsche-post-stamps-via-the-command-line-on-a-brother-ql-label-printer/Thu, 11 Jan 2024 00:00:00 +0000https://foosel.net/til/2024-01-11-how-to-print-deutsche-post-stamps-via-the-command-line-on-a-brother-ql-label-printer/<p><em>Update from 2024-01-12: I&rsquo;ve updated the scripts to support both 50mm and 62mm wide labels, and added some more whitespace trimming to the basic stamp. The post has been adjusted accordingly.</em></p> <p>I recently acquired a <a href="https://www.brother-usa.com/products/QL820NWB">Brother QL-820NWB label printer</a> to be able to quickly create labels for boxes and such, and ideally also print out Deutsche Post&rsquo;s &ldquo;print yourself&rdquo; stamps with it. The Deutsche Post stamp shop allows me to download PDFs targeting the 62mm wide endless labels for that printer, for the two types of stamps I&rsquo;m interested in (stamp, and address label with stamp). But my attempts in printing those directly to the printer through Gnome&rsquo;s printer integration weren&rsquo;t successful, things were too small, the cutter didn&rsquo;t work etc.</p>Update from 2024-01-12: I’ve updated the scripts to support both 50mm and 62mm wide labels, and added some more whitespace trimming to the basic stamp. The post has been adjusted accordingly.

I recently acquired a Brother QL-820NWB label printer to be able to quickly create labels for boxes and such, and ideally also print out Deutsche Post’s “print yourself” stamps with it. The Deutsche Post stamp shop allows me to download PDFs targeting the 62mm wide endless labels for that printer, for the two types of stamps I’m interested in (stamp, and address label with stamp). But my attempts in printing those directly to the printer through Gnome’s printer integration weren’t successful, things were too small, the cutter didn’t work etc.

I knew that printing to the printer via my local instance of brother_ql_web works flawlessly, and that the library this is based on, brother_ql, has a command line interface. So I thought, why not just convert the PDFs to individual PNGs, and then print those?

Through the magic of some shell scripting, I’m now able to do just that, right from the command line.

I installed the brother_ql Python package via pip:

pip install --user brother_ql

I had to do a little manual patch to make it work with the latest versions of the required Pillow dependency, by editing brother_ql/conversion.py and changing Image.ANTIALIAS to Image.LANCZOS.

I also made sure my .bash_profile contains the address and model of my printer:

export BROTHER_QL_PRINTER=tcp://192.168.x.x
export BROTHER_QL_MODEL=QL-820NWB

Then I created two shell scripts, one for printing stamps and one for printing labels.

The first one, porto_print, takes care of printing the stamps. It resizes, trims, adds a new border and then extends to the native width for the selected label size (50mm by default, or 62mm if requested) while keeping a right alignment:

#!/bin/bash

# Usage:
#
#   porto_print <pdf> [50|62]

#!/bin/bash

tmpdir=$(mktemp -d)

cleanup() {
  rm -rf "$tmpdir"
}
trap cleanup EXIT

PDF=$1
LABEL=${2:-50}
PNG=$(basename "${PDF%.*}")

case $LABEL in
  "50")
    WIDTH="554"
    ;;
  "62")
    WIDTH="696"
    ;;
  *)
    echo "Unsupported label size: $LABEL"
    exit -1
    ;;
esac

echo "Converting PDF to individual PNGs..."
pdftoppm "$PDF" "$tmpdir/$PNG" -png -r 600

for file in $(ls $tmpdir/*.png); do
  echo "Printing $file..."
  mogrify -background white -bordercolor white -resize 696x -trim -border 25x25 -gravity east -extent ${WIDTH}x284 "$file"
  brother_ql print -l $LABEL "$file" 
done

The second one, porto_address_print, does basically the same, just with slightly different parameters and left alignment:

#!/bin/bash

# Usage:
#
#   porto_address_print <pdf>

tmpdir=$(mktemp -d)

cleanup() {
  rm -rf "$tmpdir"
}
trap cleanup EXIT

PDF=$1
LABEL=${2:-50}
PNG=$(basename "${PDF%.*}")

case $LABEL in
  "50")
    WIDTH="554"
    ;;
  "62")
    WIDTH="696"
    ;;
  *)
    echo "Unsupported label size: $LABEL"
    exit -1
    ;;
esac

echo "Converting PDF to individual PNGs..."
pdftoppm "$PDF" "$tmpdir/$PNG" -png -r 600

for file in $(ls $tmpdir/*.png); do
  echo "Printing $file..."
  mogrify -bordercolor white -background white -resize 696x -trim -border 25x25 -gravity West -extent ${WIDTH}x839 "$file" 
  brother_ql print -l $LABEL "$file" 
done

Both of these were placed under ~/.local/bin and made executable. I can now call them both from anywhere on the command line, just passing the path to the PDF to print.

The result is one or more nicely printed stamps or address labels, ready to be stuck to an envelope:

Printed stamp and printed stamp with address label, freshly printed from example files through the two scripts

Now, this should hopefully make it easier for me to print all those address labels for OctoPrint sticker shipments in the future ;) Next step: Automated QR code labels for the various boxes on my shelves ^^

]]>How to trim screenshots via the commandlinehttps://foosel.net/til/2023-02-09-how-to-trim-screenshots-via-the-commandline/Thu, 09 Feb 2023 00:00:00 +0000https://foosel.net/til/2023-02-09-how-to-trim-screenshots-via-the-commandline/<p>I just had to trim a bunch of screenshots that had some black borders around them. I didn&rsquo;t want to do this manually or via a GUI, but ideally batch-able via the commandline. Thankfully, that&rsquo;s one of the many things that <a href="https://imagemagick.org/">ImageMagick</a> can do for you.</p> <p>I put all my screenshot PNGs into a folder, and then in that folder ran this <a href="https://imagemagick.org/script/mogrify.php"><code>mogrify</code></a> command:</p> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>magick mogrify -trim -define trim:percent-background<span style="color:#f92672">=</span>0% -background black -path output/ *.png </span></span></code></pre></div><p>I found that I had to add the <code>-define trim:percent-background=0%</code> option to get rid of <em>all</em> black borders, as otherwise on some of the images a very slim one ended up remaining. I also specified the background color with <code>-background black</code> to make sure that it really only trimmed the black borders.</p>I just had to trim a bunch of screenshots that had some black borders around them. I didn’t want to do this manually or via a GUI, but ideally batch-able via the commandline. Thankfully, that’s one of the many things that ImageMagick can do for you.

I put all my screenshot PNGs into a folder, and then in that folder ran this mogrify command:

magick mogrify -trim -define trim:percent-background=0% -background black -path output/ *.png

I found that I had to add the -define trim:percent-background=0% option to get rid of all black borders, as otherwise on some of the images a very slim one ended up remaining. I also specified the background color with -background black to make sure that it really only trimmed the black borders.

I then could combine the resulting images into a PDF with img2pdf1:

img2pdf --output output.pdf *.png

  1. Look, a hidden bonus TIL! ↩︎

]]>How to quickly generate a QR Code with transparent backgroundhttps://foosel.net/til/2023-02-06-how-to-quickly-generate-a-qr-code-with-transparent-background/Mon, 06 Feb 2023 00:00:00 +0000https://foosel.net/til/2023-02-06-how-to-quickly-generate-a-qr-code-with-transparent-background/<p>For an upcoming presentation I wanted to quickly generate a QR Code of my web site&rsquo;s URL to include on the final slide. Since my slide theme has a green gradient background with white text, I wanted the QR Code to be white on a transparent background, as a PNG.</p> <p>Enter <a href="https://github.com/soldair/node-qrcode">node-qrcode</a> which runs easily via <code>npx</code><sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup>:</p> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>npx qrcode -o output.png -d FFFF -l <span style="color:#ae81ff">0000</span> -w <span style="color:#ae81ff">500</span> <span style="color:#e6db74">&#34;https://foosel.net&#34;</span> </span></span></code></pre></div><ul> <li><code>-o output.png</code> sets the output file</li> <li><code>-d FFFF</code> sets the dark color (usually black) to white with 100% opacity</li> <li><code>-l 0000</code> sets the light color (usually white) to black with 0% opacity - fully transparent</li> <li><code>-w 500</code> sets the size to 500px</li> </ul> <p>For further options like error correction or QR code version, or how to use it as a library or in the browser, see node-qrcode&rsquo;s repo linked above.</p>For an upcoming presentation I wanted to quickly generate a QR Code of my web site’s URL to include on the final slide. Since my slide theme has a green gradient background with white text, I wanted the QR Code to be white on a transparent background, as a PNG.

Enter node-qrcode which runs easily via npx1:

npx qrcode -o output.png -d FFFF -l 0000 -w 500  "https://foosel.net"
  • -o output.png sets the output file
  • -d FFFF sets the dark color (usually black) to white with 100% opacity
  • -l 0000 sets the light color (usually white) to black with 0% opacity - fully transparent
  • -w 500 sets the size to 500px

For further options like error correction or QR code version, or how to use it as a library or in the browser, see node-qrcode’s repo linked above.

I for one am happy with the result of this little exercise:

The final slide of a presentation. It says “Thank you for you attention!”. Below that I’ve listed my Mastodon account @foosel@chaos.social, my GitHub account @foosel and my website’s address foosel.net. A big white QR Code is placed right underneath, a handdrawn arrow points from website to code.

  1. Yes, there are also online services that can do this for you, no, I didn’t want to look through dozens of them trying to find one that didn’t attempt to make me subscribe to something just to change the color of the generated QR code. Local CLI ftw. ↩︎

]]>How to use jq to extract new posts from a JSON Feedhttps://foosel.net/til/2023-02-02-how-to-use-jq-to-extract-new-posts-from-a-json-feed/Thu, 02 Feb 2023 00:00:00 +0000https://foosel.net/til/2023-02-02-how-to-use-jq-to-extract-new-posts-from-a-json-feed/<p>I&rsquo;m currently looking into ways to automate some stuff around new posts on this page (be it blog or TIL post) directly during the page build on GitHub Actions. For this, I first need to be able to reliably <em>detect</em> new posts, from a bash run step. So here&rsquo;s how to do that with <a href="https://stedolan.github.io/jq/"><code>jq</code></a>.</p> <p>The idea is to get the current <a href="https://foosel.net/til/how-to-add-json-feed-support-to-hugo/"><code>feed.json</code></a> prior to publishing the page, and then compare it to the one that was just generated during the build. If there are any differences, we know that there are new posts and can trigger further actions from there.</p>I’m currently looking into ways to automate some stuff around new posts on this page (be it blog or TIL post) directly during the page build on GitHub Actions. For this, I first need to be able to reliably detect new posts, from a bash run step. So here’s how to do that with jq.

The idea is to get the current feed.json prior to publishing the page, and then compare it to the one that was just generated during the build. If there are any differences, we know that there are new posts and can trigger further actions from there.

# Get current feed.json
curl -s https://foosel.net/til/feed.json > feed.current.json

# Get new feed.json
cp public/til/feed.json feed.next.json

# Compare the two, this is where the magic happens
jq --slurpfile current til.current.json --slurpfile next til.next.json -n '$next[0].items - $current[0].items' > til.json

Let’s go through this jq command there:

  • --slurpfile <variable> <file> reads in the given files and makes it accessible as an array contained in the given variable. In this case we read in til.current.json and make it accessible as $current, and also read in til.next.json and make it accessible as $next.
  • -n doesn’t wait for input on stdin.
  • '$next[0].items - $current[0].items' subtracts the items from the new feed from the items in the current feed1.
  • > til.json writes the output to til.json.

til.json will then contain all new items (as long as there weren’t more than the feed’s item size), can be uploaded as an artifact and then used in further jobs2.

  1. The indexing (e.g. $new[0]) here is needed due to --slurpfile creating an array from the read file. I admittedly need to experiment more with this option to fully understand it, but for the purpose here it works. ↩︎

  2. My current goal is to move my announcements on Mastodon for new posts from my NodeRED install got the page build, and also send any webmentions for links contained in new posts as well. ↩︎

]]>How to grep a log for multiline errorshttps://foosel.net/til/2023-02-01-how-to-grep-a-log-for-multline-errors/Wed, 01 Feb 2023 00:00:00 +0000https://foosel.net/til/2023-02-01-how-to-grep-a-log-for-multline-errors/<p>I just found myself in the position to have to <code>grep</code> an OctoPrint log file for error log entries with attached Python stack traces. I wanted to not only get the starting line where the exception log output starts, but the full stack trace up until the next regular log line.</p> <p>The format of the lines in <code>octoprint.log</code> is a simple <code>%(asctime)s - %(name)s - %(levelname)s - %(message)s</code>, so a log with an error and attached exception looks like this:</p>I just found myself in the position to have to grep an OctoPrint log file for error log entries with attached Python stack traces. I wanted to not only get the starting line where the exception log output starts, but the full stack trace up until the next regular log line.

The format of the lines in octoprint.log is a simple %(asctime)s - %(name)s - %(levelname)s - %(message)s, so a log with an error and attached exception looks like this:

2023-01-30 17:50:45,704 - octoprint.events.fire - DEBUG - Firing event: Disconnecting (Payload: None)
2023-01-30 17:50:45,704 - octoprint.events - DEBUG - Sending action to <bound method PrinterStateConnection._onEvent of <octoprint.server.util.sockjs.PrinterStateConnection object at 0x000001635CB6EE50>>
2023-01-30 17:50:45,705 - octoprint.plugin - DEBUG - Calling on_event on action_command_notification
2023-01-30 17:50:45,705 - octoprint.plugin - DEBUG - Calling on_event on action_command_prompt
2023-01-30 17:50:45,705 - octoprint.plugin - DEBUG - Calling on_event on announcements
2023-01-30 17:50:45,705 - octoprint.plugin - DEBUG - Calling on_event on file_check
2023-01-30 17:50:45,706 - octoprint.plugin - DEBUG - Calling on_event on firmware_check
2023-01-30 17:50:45,706 - octoprint.plugin - DEBUG - Calling on_event on pluginmanager
2023-01-30 17:50:45,706 - octoprint.plugin - DEBUG - Calling on_event on softwareupdate
2023-01-30 17:50:45,706 - octoprint.plugin - DEBUG - Calling on_event on tracking
2023-01-30 17:50:45,711 - octoprint.plugin - DEBUG - Calling on_event on mqtt
2023-01-30 17:50:45,732 - octoprint.events.fire - DEBUG - Firing event: Disconnected (Payload: None)
2023-01-30 17:50:45,735 - octoprint.events - DEBUG - Sending action to <function Server.run.<locals>.<lambda> at 0x000001635BDB2CA0>
2023-01-30 17:50:45,750 - octoprint.events - ERROR - Got an exception while sending event Disconnected (Payload: None) to <function Server.run.<locals>.<lambda> at 0x000001635BDB2CA0>
Traceback (most recent call last):
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\events.py", line 197, in _work
    listener(event, payload)
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\server\__init__.py", line 1212, in <lambda>
    octoprint.events.Events.DISCONNECTED, lambda e, p: run_autorefresh()
                                                       ^^^^^^^^^^^^^^^^^
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\server\__init__.py", line 1195, in run_autorefresh
    autorefresh.stop()
    ^^^^^^^^^^^^^^^^
AttributeError: 'RepeatedTimer' object has no attribute 'stop'
2023-01-30 17:50:45,753 - octoprint.events - DEBUG - Sending action to <bound method PrinterStateConnection._onEvent of <octoprint.server.util.sockjs.PrinterStateConnection object at 0x000001635CB6EE50>>
2023-01-30 17:50:45,755 - octoprint.plugin - DEBUG - Calling on_event on action_command_notification
2023-01-30 17:50:45,756 - octoprint.server.util.sockjs - DEBUG - Socket message held back until permissions cleared, added to backlog: plugin
2023-01-30 17:50:45,758 - octoprint.plugins.action_command_notification - INFO - Notifications cleared
2023-01-30 17:50:45,758 - octoprint.plugin - DEBUG - Calling on_event on action_command_prompt
2023-01-30 17:50:45,758 - octoprint.plugin - DEBUG - Calling on_event on announcements
2023-01-30 17:50:45,759 - octoprint.plugin - DEBUG - Calling on_event on file_check
2023-01-30 17:50:45,759 - octoprint.plugin - DEBUG - Calling on_event on firmware_check
2023-01-30 17:50:45,759 - octoprint.server.util.sockjs - DEBUG - Socket message held back until permissions cleared, added to backlog: plugin
2023-01-30 17:50:45,763 - octoprint.plugin - DEBUG - Calling on_event on pluginmanager
2023-01-30 17:50:45,764 - octoprint.plugin - DEBUG - Calling on_event on softwareupdate
2023-01-30 17:50:45,764 - octoprint.plugin - DEBUG - Calling on_event on tracking

What I now wanted is for grep to spit out just the ERROR line and the attached stack trace:

2023-01-30 17:50:45,750 - octoprint.events - ERROR - Got an exception while sending event Disconnected (Payload: None) to <function Server.run.<locals>.<lambda> at 0x000001635BDB2CA0>
Traceback (most recent call last):
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\events.py", line 197, in _work
    listener(event, payload)
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\server\__init__.py", line 1212, in <lambda>
    octoprint.events.Events.DISCONNECTED, lambda e, p: run_autorefresh()
                                                       ^^^^^^^^^^^^^^^^^
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\server\__init__.py", line 1195, in run_autorefresh
    autorefresh.stop()
    ^^^^^^^^^^^^^^^^
AttributeError: 'RepeatedTimer' object has no attribute 'stop'

For this I needed a way to set grep to match multiple lines and do a (non-matching) look ahead for the end. It turns out that the secret to success here is to treat the whole input as one line, use Perl compatible regex mode, and make sure to set the multiline flag. After some fiddling around on regex101.com and reading up on Perl’s regex options1, I came up with the following:

grep -Pazo '(?m)^\N+\- ERROR \-\N*\n(^\N*?\n)*?(?=\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2},\d{3} \- )' octoprint.log

Let’s walk through this:

  • -P enables Perl compatible regex mode
  • -a enables text mode
  • -z turns all newlines into null bytes and thus treats the whole input as a single line for finding matches2
  • -o only outputs the matched part of the line (otherwise we’d get the whole file printed out)
  • (?m) enables multiline mode
  • ^\N+\- ERROR \-\N*\n matches the first line of the error, which is the one that starts with the timestamp and package and contains the word ERROR
  • (^\N*?\n)*? non-greedily matches all following lines of the error, which are anything but a newline followed by a newline
  • (?=\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2},\d{3} \- ) is a positive look-ahead that matches a line starting with a timestamp again, which signifies the end of the error’s lines

Hooray, it works 🥳:

❯ grep -Pazo '(?m)^\N+\- ERROR \-\N*\n(^\N*?\n)*?(?=\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2},\d{3} \- )' octoprint.log
2023-01-30 17:50:45,750 - octoprint.events - ERROR - Got an exception while sending event Disconnected (Payload: None) to <function Server.run.<locals>.<lambda> at 0x000001635BDB2CA0>
Traceback (most recent call last):
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\events.py", line 197, in _work
    listener(event, payload)
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\server\__init__.py", line 1212, in <lambda>
    octoprint.events.Events.DISCONNECTED, lambda e, p: run_autorefresh()
                                                       ^^^^^^^^^^^^^^^^^
  File "C:\Devel\OctoPrint\OctoPrint\src\octoprint\server\__init__.py", line 1195, in run_autorefresh
    autorefresh.stop()
    ^^^^^^^^^^^^^^^^
AttributeError: 'RepeatedTimer' object has no attribute 'stop'

(And yes, I’ve fixed the error that lead to this stack trace as well 😉)

  1. I don’t know about you, but I always forget about positive/negative look-ahead/behind and pattern-match modifiers. ↩︎

  2. The downside of this is that now -n (print line number of match) will not work anymore and just happily report line 1 for every single match. ↩︎

]]>How to detect Termux in a scripthttps://foosel.net/til/2023-01-23-how-to-detect-termux-in-a-script/Mon, 23 Jan 2023 00:00:00 +0000https://foosel.net/til/2023-01-23-how-to-detect-termux-in-a-script/<p>If you need to detect whether you are running in Termux from a bash script, check if <code>$PREFIX</code> contains the string <code>com.termux</code>:</p> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>echo $PREFIX | grep -o <span style="color:#e6db74">&#34;com.termux&#34;</span> </span></span></code></pre></div><p>This can also be used to set a variable in a <a href="https://taskfile.dev">Taskfile</a>:</p> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-yaml" data-lang="yaml"><span style="display:flex;"><span><span style="color:#f92672">vars</span>: </span></span><span style="display:flex;"><span> <span style="color:#f92672">TERMUX</span>: <span style="color:#e6db74">&#39;{{and .PREFIX (contains &#34;com.termux&#34; .PREFIX)}}&#39;</span> </span></span></code></pre></div><p><a href="https://www.reddit.com/r/termux/comments/co46qw/how_to_detect_in_a_bash_script_that_im_in_termux/">Source</a></p>If you need to detect whether you are running in Termux from a bash script, check if $PREFIX contains the string com.termux:

echo $PREFIX | grep -o "com.termux"

This can also be used to set a variable in a Taskfile:

vars:
  TERMUX: '{{and .PREFIX (contains "com.termux" .PREFIX)}}'

Source

]]>How to determine an RPi kernel version and build without booting ithttps://foosel.net/til/2022-06-16-how-to-determine-an-rpi-kernel-version-and-build-without-booting-it/Thu, 16 Jun 2022 00:00:00 +0000https://foosel.net/til/2022-06-16-how-to-determine-an-rpi-kernel-version-and-build-without-booting-it/<p>To figure out the kernel version and build without booting it, e.g. to install matching device drivers during an automated image build in something like <a href="https://github.com/OctoPrint/CustoPiZer">CustoPiZer</a>, use something like this:</p> <div class="highlight"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="color:#66d9ef">function</span> version_and_build_for_kernelimg<span style="color:#f92672">()</span> <span style="color:#f92672">{</span> </span></span><span style="display:flex;"><span> kernelimg<span style="color:#f92672">=</span>$1 </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span> <span style="color:#75715e"># uncompressed kernel?</span> </span></span><span style="display:flex;"><span> output<span style="color:#f92672">=</span><span style="color:#66d9ef">$(</span>strings $kernelimg | grep <span style="color:#e6db74">&#39;Linux version&#39;</span> <span style="color:#f92672">||</span> echo<span style="color:#66d9ef">)</span> </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> <span style="color:#f92672">[</span> -z <span style="color:#e6db74">&#34;</span>$output<span style="color:#e6db74">&#34;</span> <span style="color:#f92672">]</span>; <span style="color:#66d9ef">then</span> </span></span><span style="display:flex;"><span> <span style="color:#75715e"># compressed kernel, needs more work, see https://raspberrypi.stackexchange.com/a/108107</span> </span></span><span style="display:flex;"><span> pos<span style="color:#f92672">=</span><span style="color:#66d9ef">$(</span>LC_ALL<span style="color:#f92672">=</span>C grep -P -a -b -m <span style="color:#ae81ff">1</span> --only-matching <span style="color:#e6db74">&#39;\x1f\x8b\x08&#39;</span> $kernelimg | cut -f <span style="color:#ae81ff">1</span> -d :<span style="color:#66d9ef">)</span> </span></span><span style="display:flex;"><span> dd <span style="color:#66d9ef">if</span><span style="color:#f92672">=</span>$kernelimg of<span style="color:#f92672">=</span>kernel.gz skip<span style="color:#f92672">=</span>$pos iflag<span style="color:#f92672">=</span>skip_bytes </span></span><span style="display:flex;"><span> output<span style="color:#f92672">=</span><span style="color:#66d9ef">$(</span>gzip --decompress --stdout kernel.gz | strings | grep <span style="color:#e6db74">&#39;Linux version&#39;</span> <span style="color:#f92672">||</span> echo<span style="color:#66d9ef">)</span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">fi</span> </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span> version<span style="color:#f92672">=</span><span style="color:#66d9ef">$(</span>echo $output | awk <span style="color:#e6db74">&#39;{print $3}&#39;</span> | tr -d <span style="color:#e6db74">&#39;+&#39;</span><span style="color:#66d9ef">)</span> </span></span><span style="display:flex;"><span> build<span style="color:#f92672">=</span><span style="color:#66d9ef">$(</span>echo $output | awk -F<span style="color:#e6db74">&#34;#&#34;</span> <span style="color:#e6db74">&#39;{print $NF}&#39;</span> | awk <span style="color:#e6db74">&#39;{print $1}&#39;</span><span style="color:#66d9ef">)</span> </span></span><span style="display:flex;"><span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">if</span> <span style="color:#f92672">[[</span> -n <span style="color:#e6db74">&#34;</span>$version<span style="color:#e6db74">&#34;</span> <span style="color:#f92672">&amp;&amp;</span> -n <span style="color:#e6db74">&#34;</span>$build<span style="color:#e6db74">&#34;</span> <span style="color:#f92672">]]</span>; <span style="color:#66d9ef">then</span> </span></span><span style="display:flex;"><span> echo <span style="color:#e6db74">&#34;Version: </span>$kernel<span style="color:#e6db74">&#34;</span> </span></span><span style="display:flex;"><span> echo <span style="color:#e6db74">&#34;Build: </span>$build<span style="color:#e6db74">&#34;</span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">else</span> </span></span><span style="display:flex;"><span> echo </span></span><span style="display:flex;"><span> echo <span style="color:#e6db74">&#34;Cannot determine kernel version and build number for </span>$kernelimg<span style="color:#e6db74">&#34;</span> </span></span><span style="display:flex;"><span> <span style="color:#66d9ef">fi</span> </span></span><span style="display:flex;"><span><span style="color:#f92672">}</span> </span></span></code></pre></div><p>Note that this has only been tested with kernels on RaspberryPi OS images, YMMV.</p>To figure out the kernel version and build without booting it, e.g. to install matching device drivers during an automated image build in something like CustoPiZer, use something like this:

function version_and_build_for_kernelimg() {
    kernelimg=$1

    # uncompressed kernel?
    output=$(strings $kernelimg | grep 'Linux version' || echo)

    if [ -z "$output" ]; then
        # compressed kernel, needs more work, see https://raspberrypi.stackexchange.com/a/108107
        pos=$(LC_ALL=C grep -P -a -b -m 1 --only-matching '\x1f\x8b\x08' $kernelimg | cut -f 1 -d :)
        dd if=$kernelimg of=kernel.gz skip=$pos iflag=skip_bytes
        output=$(gzip --decompress --stdout kernel.gz | strings | grep 'Linux version' || echo)
    fi

    version=$(echo $output | awk '{print $3}' | tr -d '+')
    build=$(echo $output | awk -F"#" '{print $NF}' | awk '{print $1}')

    if [[ -n "$version" && -n "$build" ]]; then
        echo "Version: $kernel"
        echo "Build: $build"
    else
        echo
        echo "Cannot determine kernel version and build number for $kernelimg"
    fi
}

Note that this has only been tested with kernels on RaspberryPi OS images, YMMV.

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