%rec: command
%doc: shell command examples
%type: aim line
%allowed: aim cmd bin tag note shell
%unique: shell

aim: Put output into columns
cmd: ip a | grep inet | column  -ts' '
shell: sh
bin: column
tag: format

aim: Reformat file with an explicit separator (`-s`)
cmd: column -ts: /etc/passwd
shell: sh
bin: column
tag: format

aim: Sort lines into columns with names
cmd: column -ts: -N User,PW,UID,GID,Description,Home,shell -H PW,GID /etc/passwd
note: Hide some columns with `-H`.
shell: sh
bin: column
tag: format

aim: Sort lines into columns and reorder them
cmd: column -ts: -N User,PW,UID,GID,Description,Home,shell -H PW,GID -O User,Description,shell /etc/passwd 
note: Unspecified items remain.
shell: sh
bin: column
tag: format

aim: Output to json format with `-J`
cmd: column -J -ts: -H PW,GID,shell -N User,PW,UID,GID,Description,Home,shell /etc/passwd
shell: sh
bin: column
tag: format
tag: json

aim: Make a QR Code image
cmd: qrencode 'https://play.google.com/store/apps/details?id=org.briarproject.briar.android' -o "${file}".png
shell: sh
bin: qrencode
tag: qr

aim: Make a QR Coded message in the terminal
cmd: qrencode -t ansi "Hello World"
shell: sh
bin: qrencode
tag: qr

aim: Read a QR Code image
cmd: zbarimg ${file}
shell: sh
bin: qrencode
tag: qr

aim: Show wifi QR code (only with Network Manager)
cmd: nmcli device wifi show-password
shell: sh
bin: qrencode
bin: nmcli
tag: qr
tag: wifi

aim: Combine many recfiles of different types into one
cmd: sed '1i\ ' *.rec > all.rec
shell: sh
bin: sed
tag: recfiles
tag: database

aim: Combine many recfiles of the same type into one
cmd: recinf -d -t ${type} ${one}.rec > ${all}.rec
+ sed '/^%/d' ${one}.rec ${two}.rec > all.rec
note: The strange syntax used by `sed` only makes sense after using [ed](writing/ed.md)
shell: sh
bin: sed
bin: recinf
tag: recfiles
tag: database

aim: Roll a die
cmd: echo $(( RANDOM % 6+1 ))
shell: bash
tag: random

aim: Remotely edit a file with vim
cmd: vim scp://${server}/~/${file}
cmd: vim scp://${user}@${server}:${port}//${path}/${file}
shell: sh
bin: vim
bin: scp
tag: network

aim: Find and replace across all files open in vim
cmd: :bufdo! %s/${pattern}/${replacement}/g
shell: sh
bin: vim
tag: writing
tag: replace

aim: Find and replace words, but confirm each replacement
cmd: vim -c "%s/${pattern}/${replacement}/gc" -c 'wq' ${file}
shell: sh
bin: vim
tag: replace
tag: substitution
tag: TUI
tag: writing

aim: Hard reset ntp service
cmd: sudo ntpd -q -g -x -n
bin: ntpd
tag: time
tag: system


aim: Check a service
cmd: sudo systemctl status mpd
shell: sh
bin: systemd
tag: system
tag: service


aim: Recognize service changes
cmd: sudo systemctl daemon-reload
shell: sh
bin: systemd
tag: system
tag: service


aim: Start a service (it stops when the computer shuts down)
cmd: sudo systemctl taskd.service start
+ sudo systemctl daemon-reload
shell: sh
bin: systemd
tag: system
tag: service


aim: Find out why the computer takes so long to start
cmd: sudo systemd-analyze
+ sudo systemd-analyze blame
shell: sh
bin: systemd
tag: system
tag: boot


aim: See what the computer is doing
cmd: journalctl -f
shell: sh
bin: journalctl
tag: system

aim: Check your own user services:
cmd: journalctl -f
shell: sh
bin: journalctl
tag: system

aim: Follow the `ssh` daemon service
cmd: journalctl -f -u sshd
shell: sh
bin: journalctl
tag: system

aim: Find errors since a date
cmd: date=2027-01-01
+ journalctl --since=${date} --grep="EXT4-fs error"
shell: sh
bin: journalctl
tag: system

aim: Limit the journal's size to 2 gigabytes
cmd: journalctl --vacuum-size=2G
shell: sh
bin: journalctl
tag: system

aim: Log the fact that you've installed your own `dnsmasq` on your system to `journalctl`, so that you can determine why your system's broken later
cmd: logger "Installed new dnsmasq"
+ sudo journalctl -f
shell: sh
bin: journalctl
tag: system


aim: Convert markdown table to csv
cmd: mlr --imarkdown --ocsv cat ${file}.md
bin: mlr
tag: csv
tag: markdown
tag: data

aim: Convert a csv file to markdown
cmd: mlr --icsv --omd cat ${file}.csv
bin: mlr
tag: csv
tag: markdown

aim: Quickly find and open run-command files
cmd: alias rrc='$PAGER "$(find . -maxdepth 2 -name "*rc" | fzf)"'
bin: fzf
bin: find
tag: comfy

aim: Quickly hunt and kill processes
cmd: kill $(pgrep less | fzf -m --preview='ps {}')
note: Select many with shift/tab.
bin: fzf
tag: comfy

aim: Search for a short word
cmd: grep "\b${word}\b" ${file}
bin: grep
tag: search

aim: Extract words in quotes
cmd: grep -o "\b${word}\b" ${file}
bin: grep
tag: search

aim: Reformat variable for shell input
cmd: printf "%q\n" "${variable}"
bin: printf
tag: xargs
tag: stdout

aim: Find your public IP address
cmd: dig +short myip.opendns.com @resolver$((RANDOM % 4 + 1)).opendns.com
shell: bash
bin: dig
tag: ip
tag: network

aim: Turn markdown into a man page
cmd: man <(lowdown -stman ${file}.md)
cmd: top_title="Bugs in netcat"
+ someplace=LK
+ vol=Security
+ sec=6
+ lowdown -m manheader="${top_title}" -m source="${someplace}" -m volume="${vol}" -m section=${sec} -stman ${file}.md > ${file}.${sec}
+ man ./${file}.${sec}
shell: bash
bin: lowdown
bin: groff
bin: man
tag: markdown

aim: Convert jpg to png
cmd: magick ${input}.jpg ${output}.png
bin: magick
tag: vision

aim: Reduce jpg size by reducing quality
cmd: quality=70
+ magick ${input}.jpg -quality ${quality} ${output}.jpg
cmd: size=50
+ magick -resize ${size}% ${input}.jpg ${output}.jpg
bin: magick
tag: vision

aim: Reduce png size
cmd: magick ${input}.png png8:${output}.png
bin: magick
tag: vision

aim: Invert jpg colours
cmd: magick ${input}.jpg ${output}.jpg -negate
bin: magick
tag: vision

aim: Make jpg smaller
cmd: magick ${input}.jpg -resize 25% ${output}.jpg
bin: magick
tag: vision

aim: Trim images to border
cmd: magick -trim ${image}.png ${output}.png
bin: magick
tag: vision

aim: Make the white of an image transparent
cmd: magick -transparent white -fuzz 10% ${input}.png ${output}.png
bin: magick
tag: vision
note: The 'fuzz' option tells the computer that 'close to white' is fine.  You might want to use 20% or higher fuzz.

aim: Give transparrent image a dropshadow
cmd: magick ${input}.png \( +clone -background black -shadow 50x8+0+5 \) +swap -background none -layers merge +repage ${output}.png
bin: magick
tag: vision

aim: Convert every jpg in directory to png
cmd: mogrify -format png *.jpg
bin: magick
tag: vision

aim: Convert from jpg to svg
cmd: magick -flatten ${input}.jpg ${output}.ppm
+ potrace -s ${output}.ppm -o ${svgout}.svg
bin: magick
tag: vision

aim: Make an image showing day of the week
cmd: magick -list font
+ font="$(magick -list font | grep -oP 'Font: \K.*' | head -1)"
+ 
+ magick -fill blue -font "${font}" -gravity center -pointsize 79 label:$(date +%A) day.png
bin: magick
tag: vision

aim: Make a meme
cmd: magick ${input} -font impact -fill white -pointsize 84 -stroke black -strokewidth 3 -gravity north -annotate +0+20 'TOP MEME TEXT' -gravity south -annotate +0+20 'BOTTOM MEME TEXT' ${output}
bin: magick
tag: vision
tag: memes

aim: Rotate a video
cmd: ffmpeg -i "${input}" -vf "transpose=1" "${out.mov}"
note: 
+ | No. | Degrees | Flip                                   |
+ |:---:|:-------:|:---------------------------------------|
+ | 0   | 90 Counterclockwise and verfical flip (default)  |
+ | 1   | 90 Clockwise                                     |
+ | 2   | 90 CounterClockwise                              |
+ | 3   | 90Clockwise and vertical flip                    |
tag: vision
tag: video
shell: sh

aim: Translate a media file to a new type
cmd: ffmpeg -formats
+ ffmpeg -i ${input} ${output}
bin: ffmpeg
tag: vision
tag: music
tag: video
shell: sh

aim: Reduce video quality
cmd: quality=20
+ ffmpeg -i ${input}.mp4 -vcodec libx264 -crf ${quality} ${output}.mp4
note: A crf quality of 18 is high, while 24 is low quality.
bin: ffmpeg
tag: vision
tag: video
shell: sh

aim: Convert from mkv to mp4 with a codec
cmd: ffmpeg -i ${input}.mkv -codec copy ${output}.mp4
note: Both mp4 and mkv are wrappers around other formats, so this conversion loses less quality than other conversion types.
bin: ffmpeg
tag: vision
tag: video
shell: sh


aim: Convert video to audio
cmd: ffmpeg -i ${input}.mp4 -vn ${output}.mp3
bin: ffmpeg
tag: vision
tag: video
shell: sh

aim: Convert all mkv files to mp4
cmd: for i in *.mkv; do
+ ffmpeg -i "$i" -codec copy "${i%.*}.mp4"
+ done
bin: ffmpeg
tag: vision
shell: sh


aim: Change resolution
cmd: ffmpeg -i ${input}.mp4 -filter:v scale=1280:720 -c:a copy ${output}.mp4
bin: ffmpeg
tag: vision
shell: sh

aim: Change video aspect ratio
cmd: ffmpeg -i input.mp4 -aspect 16:9 output.mp4
bin: ffmpeg
tag: vision
tag: video
shell: sh

aim: Trim video to start and stop times
cmd: start=00:00:50
+ stop=50
+ ffmpeg -i ${input}.mp4 -ss ${start} -codec copy -t ${stop} ${output}.mp4
note: The `$stop` time shows how many seconds after the start you want.
bin: ffmpeg
tag: vision
shell: sh

aim: Compress a video file
cmd: quality=21
+ ffmpeg -i ${input}.mp4 -vf scale=1280:-1 -c:v libx264 -preset veryslow -crf ${quality} ${output}.mp4
note: A crf quality of 18 is high, while 24 is low quality.
bin: ffmpeg
tag: vision
tag: video
shell: sh

aim: Convert video to a series of images
cmd: framerate=1
+ format=image2
+ ffmpeg -i input.mp4 -r ${framerate} -f ${format} image-%2d.png
bin: ffmpeg
tag: vision
shell: sh

aim: Add subtitles to a video file
cmd: fmpeg -i ${input}.mp4 -i subtitle.srt -map 0 -map 1 -c copy -c:v libx264 -crf 23 -preset veryfast ${output}.mp4
bin: ffmpeg
tag: vision
shell: sh

aim: Convert a web page to markdown
cmd: curl -sL "${url}" | html2markdown > "${file}}".md
cmd: curl -sL "${url}" | html2text > "${file}}".md
note: The `[html2markdown](https://github.com/JohannesKaufmann/html-to-markdown)` and `html2md` programs works better than any other.
bin: html2markdown
bin: curl
tag: writing
tag: web
shell: sh

aim: Decode a URL with function
cmd: urldecode() { echo -e "${@//%/\\x}"; }
+ urldecode "${magnet}"
tag: web
shell: bash

aim: Request a definition from the terminal.
cmd: word='abderian'
+ curl -s dict://dict.org/define:${word}:
cmd: function wotsa(){
+ 	def="$(curl -s dict://dict.org/define:${1// /+}: | grep -vP '^\d\d\d ')"
+ 	if [ "$def" = "" ]; then
+ 		echo no definition
+ 	else
+ 		echo "$def" | $PAGER
+ 	fi
+ }
bin: curl
tag: writing
tag: comfy
tag: dict
shell: sh