Useful commands and scripts

Some here are scripts, those begin with a shebang

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#!

• replace in place with sed
• -u to turn off buffering for sed
• pz (pythonize shell)
• Vi(m)
• Bash job control
• grep
• mail
• moreutils
• data structure or configuration processing tools
• linkchecker
• ncdu equivalent
• Faster alternatives written in Rust
• pass
• find and play videos flexibly
• Rude wget robot to recursively download a site
• ImageMagick
• FFMpeg

replace in place with sed

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sed -i -e 's/^/#/' filename

-u to turn off buffering for sed

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dmesg -T --follow | sed -u -e "s/^/$HOSTNAME/"

pz (pythonize shell)

operate on s (the line variable).

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echo -e "example\nwikipedia" | pz 's += ".com"'

Vi(m)

• Show shell executable.

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   :set shell?
  

• Execute a child shell process. Exiting returns to vi.

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   :sh
  

• Run given shell commands and exit after pressing enter.

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   :!printf ":help :!"
  

• Execute current line ('.') in sh and replace it in the vi buffer with the output.

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   :.!sh
  

• Insert the output of the shell command in the buffer.

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   :r!date
  

• Get the output of a shell command with system ( :help system ).

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   :call system('touch /tmp/$(date +%Y%m%d)')
  

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   :echo system('ls -lt /tmp/$(date +%Y)* | tail')
  

• Start a job that doesn't wait to finish ( :help job_status ), execute with no shell.

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   :call job_start(['/bin/bash', '-c', '{ sleep 60 && printf "DONE"; }'])
  

• Registers (+ * ~ / : % . -)
  • c - characterwise text
  • l - linewise text
  • b - blockwise text

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    :registers
    "+p # paste in visual mode
    

    1. unnamed register "" fills when using delete or yank
    2. numbered registers "0-"9 (deletion history stack)
    3. small delete register "- (one line or less deleted)
    4. named registers "a-"z"A-"Z (write to F gets appended, f replaced)
    5. read only registers:
       • ": most recently executed command;
       • "% current file name;
       • ". last inserted text.
    6. alternate file name register "# (in case of multiple open files)
    7. expression register "=
    8. last search result register "/
    9. GUI primary "+ and secondary "* , middle click clipboard
    10. GUI drop register "~ (drag and drop)

Bash job control

Ctrl+Z to suspend a program in bash. Sends SIGTSTP (Keyboard stop).

Start a job in the background.

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sleep 4500 &

Bash shell builtins for jobs. Applies to current shell process, not all user's shells. ####

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jobs --help

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fg # Bring to foreground. No job spec, targets shells notion of the current job
bg %1 # Sends the first job to execute in the background
wait 20110 # Process ID or job spec

Remove the second job from current shell's job list, keeping it in the process table. Not reliable for running a program in the background (in case the parent shell is destroyed).

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disown %2

Run a program in a new session. Allows bypassing potential signals from initial parents.

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setsid --fork sleep 3600 # always create a new process

Format text in a way that is safe to use as shell input.

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printf '%q\n' "It's magic!"

grep

Search directory recursively for lines starting 0 or more whitespace and $.

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grep -ER '^(\w*)\$'

mail

mailutils.txt

3.5.2.1 Syntax of mail internal commands

Open the default inbox (mbox) instead of the spool file.

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mail -f

With mail open, match string from the body.

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h :/\\[SPAM\\]

Match string from the header From.

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h From:/root

Header is Subject if omitted. Escaped to prevent an attempt to POSIX regex match.

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h /\\[SPAM\\]

Delete matching messages.

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d /\\[SPAM\\]

moreutils

• chronic: runs a command quietly unless it fails
• combine: combine the lines in two files using boolean operations
• errno: look up errno names and descriptions
• ifdata: get network interface info without parsing ifconfig output
• isutf8: check if a file or standard input is utf-8
• ifne: run a command if the standard input is not empty
• lckdo: execute a program with a lock held (deprecated)
• mispipe: pipe two commands, returning the exit status of the first
• parallel: run multiple jobs at once
• pee: tee standard input to pipes
• sponge: soak up standard input and write to a file
• ts: timestamp standard input
• vidir: edit a directory in your text editor
• vipe: insert a text editor into a pipe
• zrun: automatically uncompress arguments to command

data structure or configuration processing tools

• jq
• yq
• tomlq
• rq (see: open policy agent, Rego, kube-mgmt)

linkchecker

Check HTML documents and websites for broken links. Return value is 1 when

• invalid links were found or
• link warnings were found and warnings are enabled Supports clamav integration.

ncdu equivalent

For when ncdu is not installed.

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du -d1 -h | sort -h

Faster alternatives written in Rust

fd - alternative to find. debian package name fd-find, executable name on debian is

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fdfind

ripgrep - alternative to grep. debian package name ripgrep.

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rg

pass

Unix style password management script, encrypts with gpg.

find and play videos flexibly

Using mpv, my preferred video player.

To use as is, create a shell script with below contents, arguments:

1st argument - how long ago was the video file last changed.

The rest of the arguments: path(s) to look for videos (glob, like

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/media/videos/201*

can be used as argument).

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#!/bin/sh
find -L "${@:2}" \( -iname '*.mp4' -o -iname '*.webm' -o -iname '*.avi' \) -a -ctime -"$1" -print0 | xargs -0 mpv 

Rude wget robot to recursively download a site

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#!/bin/sh
# shows the correct script path even if called from another script
if [ -z "$1" -o -z "$2" ]; then
  echo "Usage: $(basename $(readlink -nf $0)) site_to_download_recursively destination_directory" 
  exit 1
else
  wget --continue --recursive --execute robots=off --wait 1 --directory-prefix="$2" "$1"
  # Below line for offline mirroring, test on each site.
  # wget  --mirror --convert-links --adjust-extension --page-requisites --no-parent --continue --recursive --execute robots=off --wait 1 --directory-prefix="$2" "$1"
  exit 0
fi

ImageMagick

Requires ImageMagick

Resize .jpg pictures in current directory level to roughly 1500x2000 pixels in size.

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mogrify -resize 1500x2000 *.{jpg,JPG}

Create a black background in required size (for example, to use in a video).

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convert -size 1920x1080 xc:black bg.png

FFMpeg

Dump audio using parallel. Parallel uses 1 thread for each core by default.

Make sure to change audio format according to source.

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parallel ffmpeg -i '{}' -map 0:1 -c:a copy '{.}.m4a' ::: /media/video/source_video_file.mkv