Command Line Incantations

These are command line shell snippets for useful utilities, often referred to as incantantions due to their resemblance to magic spells I suppose. I’ve written previously on Why I use the command line, and Command line alternatives to cloud products and platforms. For an intro to using the command line, there are many introductions online, or check out my old workshop notes for Intro to the Command Line.

Getting started with the command line does feel magical as you start to learn just how easy and fast it can be. But it takes time building up your spellbook. This page aims to be a place to find many of these starter scripts. Adapt and improve them to your needs.

This is a living page. I will try to return and add more snippets to this page over time.

File conversions - Video

Convert between video file formats.

dependencies:

• ffmpeg

ffmpeg -i input.avi -c:v copy -c:a copy output.mp4

File conversions - Text

Concat (combine one after another) pdf files

Combine all of the pdf files in a folder.

dependencies:

• ghostscript

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=output.pdf *.pdf

markdown to pdf

Convert a markdown file to a pdf file.

dependencies:

• pandoc
• weasyprint

pandoc -s input.md --pdf-engine weasyprint -o output.pdf

pdf to plaintext

This has evolved to a more complex script that converts pdf pages to images, OCR scans each of them, runs a spell checker with autocorrect, then recombines them together into a single text file.

dependencies:

• tesseract-ocr
• ghostscript
• sed
• aspell

code gist

File conversion - Audio

Wave file to mp3

Convert audio between formats.

dependencies:

• sox

sox input.wav output.mp3

Other Audio

Trim audio recording down to one second

Take any length any file and trim it to a smaller section.

dependencies:

• sox

sox input.wav output.wav trim 0 1

Concat (Combine one after another) two audio files

Place audio snippets one after another in a new file.

dependencies:

• sox

sox a.wav b.wav c.wav concatenated.wav

Combine audio (mix sound on sound)

Blend two sound files together.

dependencies:

• sox

sox -m a.wav b.wav c.wav mixed.wav

Reduce volume by 12dB

Change volume of a file.

dependencies:

• sox

sox speech.wav output.wav gain -12

Play internet radio

There are many dedicated internet radio streaming programs, such as pyradio, which has a nice text user interface, but this simple command works too.

dependencies:

• sox

play -t mp3 https://infraordinary.fiveradiostations.com:8443/stream

Add reverb to audio

Add some reverb to dry sound recordings.

dependencies:

• sox

sox input.wav output.wav reverb 50 50 100

Other file manipulation

Rename files ordered numerically - Bash shell

This snippet renames all jpg files in a directory from alphabetic to numeric order. The 02d means generate file numbers 00-99. Use 3d for 000-999.

i=1
for f in *.jpg 
    do mv "$f" "$( printf "%02d.jpg" $i )" 
    ((i++))
done

Rename files ordered numerically - Fish shell

set i 1
for f in *.jpg
    mv "$f" (printf "%02d.jpg" $i)
    set i (math "$i + 1")
end

Web Design

Starter CSS

This is an example of a minimal CSS stylesheet to help make a site with article text easier to read. This blog and website for example is built up from a starter like this.

body { 
  max-width: 65ch; 
  padding: 0.5rem; 
  margin: 0 auto;
}

blockquote {
  border-left: 0.25rem solid darkseagreen;
  padding-left: 1rem;
}