Linux on Raveen Kumar

fc fix command or fix previous command

Fri, 12 May 2023 00:00:00 +0000

In Bash, fc stands for “fix command” and it is a built-in command that allows you to work with the command history. The fc command provides a way to view, edit, and re-execute commands from your command history.

Here are some common uses of the fc command:

Viewing command history: You can use fc -l or simply fc to display the list of recently executed commands. By default, it shows the most recent commands with line numbers.

Grep for files that does not contain a specific string

Tue, 09 May 2023 00:00:00 +0000

Another useful way to use grep is for printing file names that do not contain a specific string, for example

grep -L "string" *

You can use the -L option of the grep command, which prints the names of all files that do not contain the specified search string.

The * at the end tells grep to search all files in the current directory. If you want to search only specific files or directories, you can replace the * with the filenames or directory names.

Periodically run a program and watch the output

Fri, 05 May 2023 00:00:00 +0000

watch

Execute a program periodically, showing output fullscreen

Example

watch ls

alternative - viddy

Horizontally print file contents

Wed, 03 May 2023 00:00:00 +0000

To concatenate the contents of a vertical file horizontally in Unix, you can use the paste command with the -s option.

Here’s an example:

Let’s say you have a file file.txt with the following vertical content:

apple
banana
orange

You can concatenate the contents horizontally using the following command:

paste -s file.txt

This will produce the output:

apple   banana  orange

The -s option tells paste to concatenate the lines horizontally instead of vertically. By default, paste separates the columns with a tab character. If you want to use a different separator, you can specify it with the -d option followed by the separator character. For example:

rsync is weird, does not sync "tags" directory

Fri, 24 Feb 2023 00:00:00 +0000

For whatever reason rsync decided not to sync tags directory since it is ignored in CVS mode. Took a lot time to figure out the problem. Finally this command works correctly.

--include used to sync everything, despite ofthe cvs option, -C. But removed in this command.

	rsync -av --delete --checksum --copy-links -rPuzhi ./public/ root@raveenkumar.xyz:/var/www/raveenkumar/

Programming

Sun, 19 Feb 2023 00:00:00 +0000

AWK

Sat, 18 Feb 2023 00:00:00 +0000

Example 1

awk -F ',' '{print $NF}' {{filename}}

To print only rows with columns matching a specific string

awk '$3 == "hello"' file

This will match with, 1 2 hello something but not with, 1 2 world something

Example 2: Awking and cutting some stuff

Lets assume that you want to print the 1st and 3rd field in one line.

echo "A:B:C:D:E:F:G" | awk -F ':' 'ORS=" " {print $1} {print $3}'

Here ORS stands for, The output record separator, by default its a newline.

Cat

Sat, 18 Feb 2023 00:00:00 +0000

Join multimedia files

cat movie.mpeg.0* > movie.mpeg
cat *mp3 > combined.mp3

cp

Sat, 18 Feb 2023 00:00:00 +0000

Dereference / follow and copy symbolic links

cp -L source dest

COPY ONLY FILE THAT DO NOT EXIST IN THE DESTINATION DIRECTORY - UPDATE

cp -u *.html destination

Cut

Sat, 18 Feb 2023 00:00:00 +0000

Cut from 25th column

https://superuser.com/questions/316785/is-there-a-diff-utility-that-allows-you-to-exclude-columns

cut -c25- file.txt

Cut fields

echo "1:2:3" | cut -d ":" -f 1

1

du

Sat, 18 Feb 2023 00:00:00 +0000

Find size of all files and directories under current directory and sort it based on size

du -sh * | sort -h

Locate

Sat, 18 Feb 2023 00:00:00 +0000

Description

Locate is a alternative to find for files. Locate uses updatedb command to update its database. Note that we must run the updatedb command everytime there is file system change.

Example

Create a database

updatedb

Locate files

locate filename

Create a database locally

updatedb_path="$HOME/.local/locate_db"
updatedb_home="$updatedb_path/home.db"
updatedb -l 0 -o "$updatedb_home" -U ~/

Locate files for locally created database

locate -d "$updatedb_home"

pandoc

Sat, 18 Feb 2023 00:00:00 +0000

https://pandoc.org/MANUAL.html

pandoc -o output.html input.txt

Sed

Sat, 18 Feb 2023 00:00:00 +0000

To replace text

sed 's/text/replacement_text/g' <file_name>

To replace text and write file

sed -i 's/text/replacement_text/g' <file_name> ** Append to beginning of a file sed -i ‘1i text’ file.txt * back

Find and replace a specific line from all files in current directory matching a specific extension

Here, all .md files have

<a id="org55550fd"></a>

Line in it. The following command deletes those lines from all the files.

find . -iname "*.md" -exec sed -i '/<a id=*/d' {} \;

TMUX

Sat, 18 Feb 2023 00:00:00 +0000

The greatest samurai to ever exist?

TMUX plugins

GitHub - tmux-plugins/tpm: Tmux Plugin Manager

GitHub - tmux-plugins/tmux-urlview: Quickly open any url on your terminal window!

GitHub - tmux-plugins/tmux-resurrect: Persists tmux environment across system restarts.

To move a pane from another window to current window

join-pane -s target-window:target-pane

To use 256 colours in Tmux

256 colours in TMUX

You should set the default terminal in .tmux.conf to be screen-256color,

set -g default-terminal "screen-256color"

Windows WSL Notes

Sat, 18 Feb 2023 00:00:00 +0000

https://thomasward.com/wsl2-x11/

Change password

To change to root user

ubuntu config --default-user root

To change password

passwd, passwd <user_name>

Open Windows GUI applications with Linux command line

mspaint.exe file.png
notepad.exe file.txt

https://dev.to/adityakanekar/upgrading-from-wsl1-to-wsl2-1fl9

bc

Fri, 17 Feb 2023 00:00:00 +0000

bc as a hex calculator

obase=16
ibase=16
9+1

bc fractional

scale=10
1/3

Evaluating expressions from commandline

bc <<< "ibase=10; obase=16; $(grep cru_spare -r | awk -F "," '{print $NF}')"

ctags

Fri, 17 Feb 2023 00:00:00 +0000

Basics

Ctags is a tool that makes it easy to navigate large source code projects. It provides some of the features that you may be used to using in Eclipse or other IDEs, such as the ability to jump from the current source file to definitions of functions and structures in other files.

For full info refer this link, https://courses.cs.washington.edu/courses/cse451/10au/tutorials/tutorial_ctags.html

Commands

cd $REPO_ROOT
ctags -R *

In vim

:! ctag -R *

Add the tags file to vimrc

Diff

Fri, 17 Feb 2023 00:00:00 +0000

To diff 2 files

diff file1 file2

To diff 2 files and view side by side

diff -y file1 file2

Example pstree command

Fri, 17 Feb 2023 00:00:00 +0000

pstree -u username -hp

ImageMagick

Fri, 17 Feb 2023 00:00:00 +0000

Adding blur effect to images convert input.jpg -blur 0x8 output.jpg

Convert a series of images to gifs convert -delay 100 -loop 0 image* animation.gif

Less

Fri, 17 Feb 2023 00:00:00 +0000

Usage

less filename

Chop long lines with `less`

less -S filename Note that -S at the end doesnot work

Linux notes general

Fri, 17 Feb 2023 00:00:00 +0000

Commands

cat - contatenate
tac - concatenate in reverse

`column` command

The column utility formats its input into multiple columns.

printf "a:b:c\n1::3\n" | column -t -s ':'

a	b	c
1	3

Note that this output is different from one that is printed in terminal. Strange… Below is the terminal output.

a	b	c
1		3

`uuidgen` universal unique id generator

Generate unique ID’s

`script` Records terminal

man script
man scriptreplay

Example

script --timing=file.tm script.out
# Write some scripts
# Exit with `exit` or `^d`
scriptreplay --timing file.tm --typescript script.out

`reset` Recover a borked terminal

Count number of files in a directory

ls -1 | wc -l

Building from source

./configure
./configure --prefix=$path

Redirections

2>&1
2>&1 > /dev/null
>
>/dev/null
>>

Keymaps

Ctrl-c
Ctrl-d
Ctrl-l

cp

cut

less

linux

seq

paste

pstree

du

rsync

sed

ssh

vifm

zip

Readline

C-x C-e to edit current commant in default text editor
or v in vi mode

`ldd` Print shared libraries

This command can be used to find all the shared library or libraries of a program

Lockfile

Fri, 17 Feb 2023 00:00:00 +0000

`lockfile`

Installation

sudo apt install procmail

Description

man lockfile

Suppose you want to make sure that access to the file “important” is serialised, i.e., no more than one program or shell script should be allowed to access it. For simplicity’s sake, let’s suppose that it is a shell script. In this case you could solve it like this:

...
lockfile important.lock
...
access_"important"_to_your_hearts_content
...
rm -f important.lock
...

Now if all the scripts that access “important” follow this guideline, you will be assured that at most one script will be executing between the lockfile and the rm commands.

paste

Fri, 17 Feb 2023 00:00:00 +0000

print 2 files side by side

paste file1 file2

-d {{delimiter}}
-d''

Ranger file manager

Fri, 17 Feb 2023 00:00:00 +0000

Managing files from commandline might be cumbersome time to time. To make the job easy there are quit a lot of terminal curses based file managers available like, ranger which uses Vi keybindings.

Installation

pip install ranger-fm

usage

ranger

keybindings

Official pages

https://ranger.github.io/documentation.html https://github.com/ranger/ranger

Tabbed mode

Ctrl-n
<Tab> key to switch between tabs

Show hidden files

Ctrl-h
zh

To cd into current curectory after exit

https://superuser.com/questions/1043806/how-to-exit-the-ranger-file-explorer-back-to-command-prompt-but-keep-the-current

alias ranger='ranger --choosedir=$HOME/.rangerdir; LASTDIR=`cat $HOME/.rangerdir`; cd "$LASTDIR"'

Open Multiple files in vim from ranger

Select all the files with ranger

rsync

Fri, 17 Feb 2023 00:00:00 +0000

Usage

rsync -P source dest

This is the command that I used for syncing this website

# For whatever reason rsync excludes tags directory, so --include used
rsync -av --delete --checksum --copy-links -rPuzhi ./public/ root@raveenkumar.xyz:/var/www/raveenkumar/

Example - Directory mirroring

rsync -PCahzvu --delete $ORIG_PATH/$ORIG_DIR $MIRROR_PATH/.

-P -C: Skip revision control files
-a: Archive 
-h: Human readable
-z: zip
-v: Verbose
-u: Update
--delete: Delete directories and files which  is present in mirror directory but not in original directory.

To exclude

--exclude=”\*/file.txt”

https://superuser.com/questions/555799/how-to-setup-rsync-without-password-with-ssh-on-unix-linux

seq

Fri, 17 Feb 2023 00:00:00 +0000

http://www.compciv.org/topics/bash/variables-and-substitution/

seq 1 5
echo $(seq 1 5)
# Or, to create 5 new directories:
# mkdir $(seq 1 5)

Slurm Job manager

Fri, 17 Feb 2023 00:00:00 +0000

To allocate 4 CPU cores and 8 GB of RAM for an emacs process using the srun command, you can use the following command:

srun --cpus-per-task=4 --mem=8192 emacs

The --cpus-per-task option specifies the number of CPU cores to allocate, and the --mem option specifies the amount of memory in megabytes.

To pass the -nw argument to emacs when using the srun command, you can simply include it after the emacs command in the srun command line. For example:

ssh

Fri, 17 Feb 2023 00:00:00 +0000

Cd to a particular dir after ssh

$ ssh -t ostechnix@192.168.225.52 'cd /home/ostechnix/dir1 ; bash'

To automatically install a ssh public key on a remote machine

ssh-copy-id -i ~/.ssh/id_rsa.pub $USER@$HOSTNAME

To manually install a ssh public key on a remote machine

cat ~/.ssh/id_rsa.pub; # copy the contents of the file; paste into ssh/authorized_keys file;
chmod 600 ~/.ssh/authorized_keys

Tar

Fri, 17 Feb 2023 00:00:00 +0000

Untar

tar -xvf file.tar dir_ext

tar

tar -cf file.tar

To compress with gunzip/gzip

tar -xvfz file.tar dir_ext

Gunzip / gzip

cat file | gzip > file.gzip

Unix find

Fri, 17 Feb 2023 00:00:00 +0000

To exclude files or perform reverse match

find . -not -iname "file"

To perform regex matching

find . -regex ".*file"

To find and print only symbolic links in a directory and its subdirectories

find . -type l -print

Bash

Thu, 16 Feb 2023 00:00:00 +0000

Bash

Reading materials

Select statement

select opt in y n; do
	echo $opt
done

This creates a loop where the user can select the option. Use case to break out of the loop.

select opt in y n; do
	echo $opt selected
	case $opt in
		y)
			break 
			;;
		n)
			break 
			;;
		*)
			echo wrong option
			;;
	esac
done

Bash variables

$USER
$HOSTNAME
$PS1

To Find or List all environment variables

env

This is useful when we want to manage the shell variables properly

GNU Make Notes

Mon, 13 Feb 2023 00:00:00 +0000

GNU Make notes

https://www.cmcrossroads.com/article/basics-getting-environment-variables-gnu-make

exit script with exit 0 or make will interpret it as error if there is no 0 returned. Context below

c - Make: *** [] Error 1 - Stack Overflow

How to shoot yourself in the foot

Tue, 07 Feb 2023 00:00:00 +0000

How to shoot yourself in the foot

Described below are several methods for shooting yourself in the foot using various programming techniques.

C
You shoot yourself in the foot.

C++
You accidentally create a dozen instances of yourself and shoot them all in the foot. Providing emergency medical care is impossible since you can’t tell which are bitwise copies and which are just pointing at others and saying, “That’s me over there.”

Creating windows 11 installation media from linux

Thu, 20 Oct 2022 00:00:00 +0000

Seems like creating windows 11 installation media is problematic without a windows os. Tried Balena Etcher, woeusb and Fedora media writer and were unable to produce bootable image.

Now trying out ventoy.

https://ventoy.net/en/download.html

Steps
1. Install ventoy into an usb storage (Note install it as GPT and not MBR for obvious reasons, more storage size support, etc.)
2. Copy downloaded iso file into ventoy usb partition
3. You can copy any number of iso into this partition it seems
4. Disable CSM support in motherboard bios
5. Restart bios
6. Enable Secure Boot in bios
  - Secure Boot mode - Standard
7. Restart bios
8. There was a error for some reason, key error, I had to enroll the key into MOK database using the options provided
9. Still it did not work, windows 11 installation reported that my system does not meet the requirements
10. Now only step 4, and not step 6.
  1. Disable CSM
  2. Disable secure boot
11. With this I was able to install

I don’t know why this has to be a pain in the butt.

How to merge pdf file in command-line

Wed, 19 Oct 2022 00:00:00 +0000

pdfunite pdf1.pdf pdf2.pdf out.pdf

pdfunite ~/my_repos/raveenkumar.xyz/Blog/linux_and_programming/vimrefcard.pdf ~/my_repos/raveenkumar.xyz/Blog/linux_and_programming/vimrefcard.pdf 2022-10-19-out.pdf

How to create and move windows and containers to workspaces on the fly in i3wm

Fri, 30 Sep 2022 00:00:00 +0000

I do not know why i3wm does not have this key-bind by default. But this piece of code solves it.

This is the task that i want the i3wm to do,

Move window to any existing workspace
If the input workspace does not exist create a new one and move the window to it.

    set $custom_command [r]ename workspace [m]ove to workspace [c]reate workspace [q]uit
    bindsym $mod+c mode "$custom_command"
    
    mode "$custom_command" {
        bindsym r exec i3-input -F 'rename workspace to "%s"' -P 'New name: '; mode "default"
        bindsym m exec "bash ~/.scripts/move_window_to_existing_workspace.bash"
        bindsym c exec i3-input -F 'workspace "%s"' -P 'New Workspace name: '; mode "default"
    
        bindsym q mode "default"
    }

~/.scripts/move_window_to_existing_workspace.bash file contents

How to create qrcodes in command-line

Fri, 30 Sep 2022 00:00:00 +0000

Install qrencode

sudo dnf install qrencode

Run the following command.

qrencode -o "test.png" "Hello World!"
# xdg-open test.png

qrencode -o "test2.png" "This is \
        a\
        multiline\
        qr-code\
      with a lot of text arsithraishtraihtsirts\
    rastarstnorastirahtensrahtierahts\
  arsnthierashtiersnhtearhtsierhsat\
ariesthresnth"
# xdg-open test2.png

How to download large files with onedrive on linux

Thu, 29 Sep 2022 00:00:00 +0000

I wanted to download about 25 GB size files on linux from onedrive but it kept hanging and failing after 50 MB sometimes it can download about 2.5 GB but still fails in-between. Tried different browsers but still it keeps failing.

These are the following steps to use linux client to download large files,

sudo dnf install onedrive

Instructions to use

https://github.com/abraunegg/onedrive/blob/master/docs/USAGE.md

https://abraunegg.github.io/

This works well. But still slow.

Battery information in i3 status bar

Tue, 27 Sep 2022 00:00:00 +0000

First create battery block,

battery 0 {
  format = " %status %percentage %remaining "
  format_down = " no battery "  
  last_full_capacity = false
  integer_battery_capacity = true  
  hide_seconds = true    
  status_chr = ""
  status_bat = "☉"
  status_full = "☻"
  low_threshold = 10
  threshold_type = percentage
  path = "/sys/class/power_supply/BAT0/uevent"
}

then add it to the order array,

order += "battery 0"

Make sure to check the path of the battery first. In my case it was /sys/class/power_supply/BAT0/uevent. It might be different for other laptops.

How to Fix touch pad 3 finger gestures not working on fedora xorg

Wed, 21 Sep 2022 00:00:00 +0000

https://github.com/JoseExposito/touchegg#readme

sudo dnf install touchegg
# You may also need to manually start the service
sudo systemctl start touchegg
sudo systemctl enable touchegg

https://github.com/JoseExposito/gnome-shell-extension-x11gestures

Install this

https://extensions.gnome.org/extension/4033/x11-gestures/

Now you will be able to get the 3 finger gestures.

How to find out what display server I am using

Thu, 15 Sep 2022 00:00:00 +0000

https://unix.stackexchange.com/questions/236498/how-to-get-information-about-which-display-server-is-running

ps -e | grep tty

How to change hostname

Tue, 13 Sep 2022 00:00:00 +0000

How to change hostname

Print hostname

hostname
hostname -I
echo $HOSTNAME

To change hostname

sudo hostname -b <New name>
sudo echo <new name> /etc/hostname

change name in /etc/hosts
If you are in wsl, add the following entry to /etc/wsl.conf

[network]
generateHosts = false

Restart computer

Start your commands with a comma

Tue, 13 Sep 2022 00:00:00 +0000

https://rhodesmill.org/brandon/2009/commands-with-comma/

Thunderbird authentication after office 365 password reset

Tue, 23 Aug 2022 00:00:00 +0000

Thunderbird authentication after office 365 password reset

https://kb.uwm.edu/uwmhd/page.php?id=109671

Setting up email server

Mon, 01 Aug 2022 00:00:00 +0000

Luke smith explains how to setup an email server. With this I am able to receive email but not able to send. I think my VPS vultr blocked my outbound smtp port 25. Opened a ticket to resolve it.

https://github.com/lukesmithxyz/emailwiz

How to use office365 email with thunderbird

Fri, 15 Jul 2022 00:00:00 +0000

How to use office365 email with thunderbird

https://uit.stanford.edu/service/office365/configure/thunderbird-oauth2

Emacs can highlight git merge conflicts in buffer

Mon, 30 May 2022 00:00:00 +0000

Emacs can highlight git merge conflicts in buffer

How to kill subprocess of a shell

Tue, 08 Feb 2022 00:00:00 +0000

How to kill subprocesses of a shell

In bash $$ will get you current process id.

You can use pkill -P $$ to kill all subprocess of the current shell.

   -P, --parent ppid,...
          Only match processes whose parent process ID is listed.

Stackoverflow answer

Linux on Raveen Kumar

fc fix command or fix previous command

Grep for files that does not contain a specific string

Periodically run a program and watch the output

watch

Horizontally print file contents

rsync is weird, does not sync "tags" directory

Programming

AWK

Example 1

Example 2: Awking and cutting some stuff

Cat

Join multimedia files

cp

Dereference / follow and copy symbolic links

COPY ONLY FILE THAT DO NOT EXIST IN THE DESTINATION DIRECTORY - UPDATE

Cut

Cut from 25th column

Cut fields

du

Find size of all files and directories under current directory and sort it based on size

Locate

Description

Example

Create a database

Locate files

Create a database locally

Locate files for locally created database

pandoc

Sed

To replace text

To replace text and write file

Find and replace a specific line from all files in current directory matching a specific extension

TMUX

TMUX plugins

To move a pane from another window to current window

To use 256 colours in Tmux

Windows WSL Notes

Change password

To change to root user

To change password

Open Windows GUI applications with Linux command line

bc

bc as a hex calculator

bc fractional

Evaluating expressions from commandline

ctags

Basics

Commands

Diff

To diff 2 files

To diff 2 files and view side by side

Example pstree command

ImageMagick

Less

Usage

Chop long lines with less

Linux notes general

Commands

column command

uuidgen universal unique id generator

script Records terminal

Example

reset Recover a borked terminal

Count number of files in a directory

Building from source

Redirections

Keymaps

Readline

ldd Print shared libraries

Lockfile

lockfile

Installation

Description

paste

print 2 files side by side

Ranger file manager

Installation

usage

keybindings

Chop long lines with `less`

`column` command

`uuidgen` universal unique id generator

`script` Records terminal

`reset` Recover a borked terminal

`ldd` Print shared libraries

`lockfile`