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UTILITIES-and-NOTES.md

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  • csplit - split a file into sections determined by context lines

  • nl - number lines of files

  • tac - concatenate and print files in reverse

  • head - output the first part of files (tail - opposite)

  • sort - sort lines of text files

  • uniq - report or omit repeated lines

  • seq - print a sequence of numbers

  • strace - trace system calls and signals

File format converter

  • pandoc

    • [MD to] PDF conversion dependencies:
      • texlive-latex-base -> pdflatex
      • lmodern -> To avoid "LaTeX Error: File `lmodern.sty' not found." error
      • texlive-fonts-recommended -> to avoid "Font T1/cmr/m/n/10=ecrm1000 at 10.0pt not loadable: Metric (TFM) file not found." error
      • texlive-latex-recommended texlive-pictures texlive-latex-extra -> recommended for more styles also avoids "LaTeX Error: File `booktabs.sty' not found." error

  • convert - convert between image formats as well as resize an image, blur, crop, de-speckle, dither, draw on, flip, join, re-sample, and much more

  • gs - Ghostscript (PostScript and PDF language interpreter and previewer)

    • can be used to downsize a PDF

      e.g., gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

      Ref: https://askubuntu.com/q/113544

    • can be used to convert colour images in a PDF to black and white (b/w). The following script could be used for that:

      #!/bin/bash
gs \
 -sOutputFile=output.pdf \
 -sDEVICE=pdfwrite \
 -sColorConversionStrategy=Gray \
 -dProcessColorModel=/DeviceGray \
 -dCompatibilityLevel=1.4 \
 -dNOPAUSE \
 -dBATCH \
 $1

      Ref: https://unix.stackexchange.com/a/93971

  • ps2pdf - Convert PostScript to PDF using ghostscript

  • qpdf - PDF transformation software

    • Removing password protection from a PDF file

      e.g., qpdf --password="$PASS" --decrypt restricted-input.pdf unrestricted-output.pdf

    Ref: https://superuser.com/a/850972/563569

  • pdftk - Password protect a new PDF file

    pdftk input.pdf output output.pdf user_pw <password | PROMPT>

    Ref: https://unix.stackexchange.com/a/187405/182996

  • zip - Create a password protected ZIP file

    zip -r --encrypt output.zip input-files/

    Ref: https://askubuntu.com/a/17643/732512

Audio & Video

  • ffmpeg - can be used for a lot of things

    • To convert *.wmafiles to *.mp3,

      for file in *.wma
do
  ffmpeg -i "${file}"  -acodec libmp3lame -ab 192k "${file/.wma/.mp3}"
done

    • To crop an audio file (without any transcoding),

      ffmpeg -ss ${start_time} -t ${time_duration_from_start} -i ${input_file} -acodec copy ${output_file}

      Examples:

      1. To remove the first 5 seconds from an audio file:

        ffmpeg -ss 0:05 -i ${input_file} -acodec copy ${output_file}

      2. To remove the last five seconds from an audio file (5:23 seconds)

        ffmpeg -t 5:18 -i ${input_file} -acodec copy ${output_file}

    • To remove audio from video file. Ref: https://superuser.com/a/268986/563569

      ffmpeg -i ${input_file} -c copy -an ${output_file}

    • To merge a set of .ts files. Ref: https://superuser.com/a/693009/563569

      cat audio_1.ts audio_2.ts audio_3.ts >all.ts
ffmpeg -i all.ts -bsf:a aac_adtstoasc -acodec copy output.mp4

    • To extract .mp3 audio from .mp4. Ref: https://stackoverflow.com/a/36324719/5614968

      ffmpeg -i input.mp4 -vn -q:a 0 -map a output.mp3

    • To reduce the size of a .mp4 file without compromising quality. Ref: https://unix.stackexchange.com/a/38380/182996

      ffmpeg -i input.mp4 -vcodec libx264 -crf 20 output.mp4

    • To merge multiple .mp4 files. Ref: https://stackoverflow.com/a/17487021/5614968

      # Create a text file (inputs.txt) with input file names. Each line
# having the following format:
#
#    file <mp4_file_name>
#
# Eg.
#
#    file input_1.mp4
#    file input_2.mp4
#    file input_3.mp4
#

# Then execute the following command
ffmpeg -f concat -i inputs.txt -vcodec copy -acodec copy concat_output.mp4

    • To cut a portion of the video in the middle without a concatenation. Ref: https://stackoverflow.com/a/65941529/5614968

      # In order to keep <start-15s> and <45s-end>, you need to 
# keep all the frames which are "not between 15s and 45s":

ffmpeg -i input.mp4 \
  -vf  "select='not(between(t,15,45))',  setpts=N/FRAME_RATE/TB" \
  -af "aselect='not(between(t,15,45))', asetpts=N/SR/TB" \
  output.mp4

  • Noise suppression LADSPA plugin - CLI

    • This is said to help with trimming the noise from the microphone and thus help with better microphone quality.

Device related

  • lsblk - list block devices

  • lsusb - list USB devices

  • lspci - list all PCI devices

Disk related

  • df - report file-system disk space usage

  • du - estimate file space usage

    Typical usage: du -hs path/to/directory

    Quickly check sizes of directoreis in one level: du -sh -- * [ Ref ]

  • fdisk - manipulate disk partition table

  • hdparm - get/set SATA/IDE device parameters

  • fsck - clean and repair a linux file-system

Display

  • xrandr - primitive command line interface to RandR extension

    It could be used to connect and configure a HDMI projector

    Possible example: xrandr --output HDMI-0 --mode 1280x720 --right-of DVI-0

General Notes

  • grep turns off colouring when piping, if it detects the destination is not a tty. To over come this use --color=always. Defining an alias for this as alias cgrep=grep --color=always would help.

    Ref: https://superuser.com/a/36045/563569

  • Sometimes less might not recognize the special ASCII control characters that were piped to it. This could be overcome by passing the -R option.

    Ref: https://superuser.com/a/117842/563569

  • Typically, if you want to page the coloured output of grep to less. You would have to do grep --color=always ... | less -R.

  • The GNOME display manager (GDM3) might not work correctly after upgrading to debian testing from debian current stable. In that case, the following should be done to restore Gnome:

    apt --reinstall install gdm3
apt --reinstall install gnome
apt --reinstall install gnome-shell
dpkg-reconfigure gdm3

    Ref: https://wiki.debian.org/DebianTesting

  • Good guide to enable input through bluetooth microphone using pipewire (pulseaudio alternative) on Ubuntu 20.04: https://askubuntu.com/a/1339908/732512

Git

  • Using filter-repo to change the e-mail address in commits:

    git filter-repo --email-callback "
  return email if email != b'old@email.com' else b'new@email.com'
  " --refs <committish>

    Related resource: Example in filter-repo

    Note:

Firefox

Windows

Batch image processing

It looks like batch image porcessing could be achieved using ImageMagick.

PowerShell was used to iterate over multiple files. A useful resource that helped with this is https://stackoverflow.com/a/18848848/5614968

The QA that helped with identifying how to crop images using ImageMagick is the following: https://stackoverflow.com/a/14825481/5614968

A PowerShell snippet used to batch crop images in a directory:

Get-ChildItem .\ |
	ForEach-Object {
		magick $_.FullName -crop +0+110 interim.jpg
		magick .\interim.jpg -crop +0-30 ($_.BaseName + '_c.jpg')
}