Print n-th column to last column

From this StackOverflow thread, this is how you can print from the n-th column to the last column of a line, using awk.

e.g. form the third column:

awk '{ print substr($0, index($0,$3)) }'

Use cases

This is useful with you want to analyse your own command's history, like:

history | awk '{print substr($0, index($0,$2))}'

Wiping a file

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

if [[ "$#" -ne 1 ]]; then
  echo "Please use this command with the filename you want to wipe. Like:"
  echo "$0 file.txt"
  exit 1
fi

_file="${1}"

_times=8
filesize=$(stat -c %s "${_file}")

# Zeroes
dd if=/dev/zero of="${_file}" bs="${filesize}" count=1 conv=notrunc
# Ones
dd if=<(yes $'\xFF' | tr -d '\n') of="${_file}" bs="${filesize}" count=1 conv=notrunc

# Random stuff
for (( i = 0; i < _times; i++ )); do
  dd if=/dev/urandom of="${_file}" bs="${filesize}" count=1 conv=notrunc
done

Made possible with the help of Securely Wipe a File with DD and How do I get an equivalent of /dev/one in Linux

How to use multiple dropbox accounts on the same computer

From How Can I Use Multiple Dropbox Accounts on the Same Computer? - The Unofficial Dropbox Wiki:

First, create an alternate (hidden) directory for your second Dropbox account:

mkdir ~/.dropbox-alt

Then run the Dropbox installer in “first use” mode, specifying the alternate home directory as follows:

HOME=~/.dropbox-alt dropbox start -i

To run the “alternate” Dropbox manually for testing:

HOME=~/.dropbox-alt ~/.dropbox-alt/.dropbox-dist/dropboxd

Create a shell script to start the alternate Dropbox daemon:

cd ~/.dropbox-alt           # change to the "alternate" Dropbox directory
                            # which was created above
gedit dropbox-alt.sh        # create a new file with the 'gedit' text editor

Copy and paste the following lines into the editor:

#!/bin/bash
HOME=$HOME/.dropbox-alt     # set the new home dir
cd                          # to the "new" $HOME
./.dropbox-dist/dropboxd &  # and run dropboxd

Set the dropbox-alt.sh script to auto-start on login!

Find and Replace string in all files

From Find and Replace string in all files recursive using grep and sed:

grep -rl $oldstring /path/to/folder | xargs sed -i s@$oldstring@$newstring@g

How to convert between formats

m4a to mp3

ffmpeg -i <file>.m4a -acodec libmp3lame -ab 128k <file>.mp3

Automatically

for file in *m4a; do echo ffmpeg -i $file -acodec libmp3lame -ab 128k ${file%.*}.mp3; done

How to remove accent characters

With the help of: http://www.linuxquestions.org/questions/linux-newbie-8/how-to-remove-accent-characters-4175431373/

find . -type f -iname "*.py" | while read file; do
    iconv -f UTF-8 -t ASCII//TRANSLIT $file > $file-tmp
    mv $file-tmp $file
done

Finding Hardware Information on Linux

From How to find information about hardware? - Linux Mint Forums

A more human readable output:

inxi -Fx

This one was super useful in discovering the name of the Motherboard I was using.

For more detailed info:

lshw

Hibernation Problems

After installing Linux Mint 20 Hibernation didn't work.

To make it work I followed this post on how to update grub and merging this post's Actions of the com.ubuntu.enable-hibernate.pkla file.

And creating the service to disable devices to wake up from hibernation as this SO guide, in my case I wanted to disable the keyboard from waking up the computer.

Merge/Join images on command line

Requires ImageMagick:

Vertical sprite:

convert image1.png image2.png image3.png -append result/result-sprite.png

Horizontal sprite:

convert image1.png image2.png image3.png +append result/result-sprite.png



Dicas Linux

How do I list all cron jobs for all users?

From How do I list all cron jobs for all users? :

# As root:
for user in $(cut -f1 -d: /etc/passwd); do echo $user; crontab -u $user -l; done

How to create a CPU spike with a bash command

From How to create a CPU spike with a bash command :

dd if=/dev/zero of=/dev/null

To run more of those to put load on more cores, try to fork it:

fulload() { dd if=/dev/zero of=/dev/null | dd if=/dev/zero of=/dev/null | dd if=/dev/zero of=/dev/null | dd if=/dev/zero of=/dev/null & }; fulload; read; killall dd

Repeat the command in the curly brackets as many times as the number of threads you want to produce (here 4 threads). Simple enter hit will stop it (just make sure no other dd is running on this user or you kill it too).

Rsync

Pegando e enviando arquivos para a Amazon

rsync -avz --progress -e "ssh -i chave.pem" ubuntu@ip:arquivo .

Apenas arquivos novos

Dicas aqui

rsync --update -raz --progress <origem> <destino>

How to gzip a directory, transfer via scp, and decompress in one command?

rsync -az --progress source_dir/* remote_host:/destination_dir # Show progress bar
#or:
tar -zc path/to/source | ssh user@remote tar -zxC path/to/destination # Doesn't show progress bar

Rsync on a different SSH port

From Is it possible to specify a different ssh port when using rsync? - Stack Overflow:

rsync -azvP -e 'ssh -p 2222' ./dir user@host:/path

Encontrando arquivos com setuid ativado

Com ajuda, conseguimos encontrar todos os arquivos que estão com setuid ativado. Isso foi útil para resolver um problema que estava dando no SAS devido ao fato dos bin não estarem setados com ele:

find . -xdev \( -perm -4000 \) -type f -print0 | xargs -0 ls -l

Para se setar o setuid basta se adicionar qual bit será será setado como steuid (u,g,o):

chmod 4444 arquivo
# ou
chmod 2444 arquivo
# ou
chmod 1444 arquivo

Mouse

Quando o touchpad parar de funcionar basta executar estes dois comandos:

# Como root:
modprobe -r psmouse
modprobe psmouse

Sort

Sort com delimitador diferente de espaços

sort -t: myFile

Sort n-ésima coluna

sort -k3,3 myFile

Sort com ordenação numérica de verdade ( 9 < 100 )

sort -n myFile

Ativando swap

Ativando swap, seguindo o tutorial da DigitalOcean:

#!/usr/bin/env bash
if [ $(id -u) -ne 0 ]; then echo "Run as root"; exit 1; fi
free -m
fallocate -l 4G /swapfile
chmod 600 /swapfile
mkswap /swapfile
swapon /swapfile
swapon -s
free -m

Loop com arquivos que têm espaços no nome

Dicas extraídas daqui e daqui.

find . -print0 | while read -d $'\0' file; do cp -v "$file" /tmp; done

find . -type f -name '*.*' -printf '%p\0' | tar --null -uf archive.tar -T -

Descobrindo a placa de vídeo

Para se decobrir qual placa de vídeo estamos usando podemos utilizar o lspci como descrito aqui e aqui:

lspci -v

Copying

Avoid copy if files exist in destination

cp -R -u -p /source /destination

Due to these options:

-p                           same as --preserve=mode,ownership,timestamps
    --preserve[=ATTR_LIST]   preserve the specified attributes (default:
                            mode,ownership,timestamps), if possible
                            additional attributes: context, links, xattr,
                            all
-R, -r, --recursive          copy directories recursively
    --reflink[=WHEN]         control clone/CoW copies. See below
    --remove-destination     remove each existing destination file before
                            attempting to open it (contrast with --force)
    --sparse=WHEN            control creation of sparse files. See below
    --strip-trailing-slashes  remove any trailing slashes from each SOURCE
                            argument
-u, --update                 copy only when the SOURCE file is newer
                            than the destination file or when the
                            destination file is missing

Displaying Today’s Files Only

find -maxdepth 1 -type f -mtime -1

How to zip files that are listed in a text file

cat input.txt | zip filename.zip -@

Desabilitando um usuário, mas sem apagá-lo

usermod --expiredate 1 [LOGIN]

passwd -l [LOGIN]

IPTables (Firewall)

Algumas dicas interessantes:

Listando as regras, com portas e número das linhas:

iptables -L -n --line-numbers

Apagando uma linha específica:

iptables -D INPUT [num]

Adicionando regra para novas conexões:

iptables -A INPUT -m state --state NEW -p tcp --dport [porta] -j ACCEPT

Regra para se rejeitar demais conexões:

iptables -A INPUT -j REJECT --reject-with icmp-host-prohibited
iptables -A INPUT -j DROP

Bloqueando acesso de saída (upload) de um IP:

iptables -A OUTPUT -d [ip-address] -j DROP

Bloqueando saída por porta:

iptables -A OUTPUT -p tcp --dport [port] -j DROP

To block tcp port for an IP address:

iptables -A OUTPUT -p tcp -d [ip address] --dport [port] -j DROP

How to run multiple simultaneous X Window sessions

From Linux Commando

  • Switch to a virtual terminal
    • By default, six virtual text terminals are available to you (Ctrl+Alt+F1 to F6)
    • Press Control+Alt+F1 to go to virtual terminal 1
  • Login as her
  • Execute the following command startx -- :1
  • This starts another X session using the first free graphical console.
    • By default, 6 X consoles are available (Ctrl+Alt+F7 to F12)
    • Your own existing X session is Ctrl+Alt+F7
    • The next free X console is therefore Ctrl+Alt+F8
  • To switch from her X session to yours, and vice versa, press Ctrl+Alt+F7 and Ctrl+Alt+F8 respectively.

You may use the above procedure to create up to 5 additional X sessions (Ctrl+Alt+F8 to Ctrl+Alt+F12). For each additional X session, increment the console number in both step 1 and 3. For instance, switch to virtual terminal 2 (Control+Alt+F2) to execute the command startx -- :2.

Create another SSH server

Sometimes you need to debug your SSH connection, for those times you can open another SSH server and watch what is happening inside it.

/usr/sbin/sshd -d -p 2222

And when (from other machine) need to connect to it:

ssh -p 2222 user@machine

No wired connection after suspend

(Not tested yet)

From this Ubuntu Forum thread:

  • Get the Kernel module with lspci -k | grep -iA3 NETWORK or lspci -k | grep -iA3 ethernet
  • Edit /etc/pm/config.d/modules
    • Add SUSPEND_MODULES="<the_kernel_module_for_your_network_card>"

Or in one shot:

lspci -k | grep -iA3 ethernet | grep -i "Kernel driver" | awk '{print $NF}'

Knowing that your Kernel module is 8139:

  1. Unload 8139:

    sudo modprobe -r 8139

  2. Suspend:

    sudo pm-suspend

  3. Resume the computer from suspend

  4. Reload the module:

    sudo modprobe 8139

  5. Test the network connection.

Validating RSA public keys

ssh-keygen -l -f key.pub

More info on How do I validate a RSA ssh public key file (id_rsa.pub)? - Server Fault

Getting you own key from the command line

To get your fingerprint

ssh-add -l

To get your public key

ssh-add -L

This is useful when you are inside a Docker container that has your keys forwarded to it using:

-v $(dirname $SSH_AUTH_SOCK):$(dirname $SSH_AUTH_SOCK)
-e SSH_AUTH_SOCK=$SSH_AUTH_SOCK

Getting home directory by username

eval echo ~$USER

How do I find out which process is eating up my bandwidth

From networking - How do I find out which process is eating up my bandwidth? - Ask Ubuntu:

sudo apt-get install -y nethogs
sudo nethogs eth0

Another way:

  • Run sudo iftop
  • Push S or D to display Source and Destination ports
  • Then use netstat -tup to discover the process

Discovering available versions of a package to install

Discover which versions are available using one of the following commands:

apt-cache policy <package-name>
apt-cache madison <package-name>

Then, to install the chosen version:

sudo apt-get install package=version

Copying text from the command line

xclip -sel clip < ~/.ssh/id_rsa.pub

Which package an executable came from?

With the help of apt - How can I tell which package an executable came from? - Ask Ubuntu there are two alternatives:

sudo apt-get install apt-file
# It takes a bit of time
sudo apt-file update
apt-file search filename

OR

dpkg-query -S [executable]

Finding the size of files older than X days

With the great help of StackOverflow:

find . -mtime +180 -exec ls -lrt {} \; | awk '{ total += $5}; END { print total }'

It will give the total size of files, in bytes.

But if you want to see the sizes in a more human readable way:

find . -mtime +180 -exec ls -lrt {} \; | awk '{ total += $5}; END { print total }' | awk '{ split( "KB MB GB" , v ); s=0; while( $1>1024 ){ $1/=1024; s++ } print int($1) v[s] }'

Create disk image

From dd - ArchWiki

Boot from a live media and make sure no partitions are mounted from the source hard drive.

Then mount the external hard drive and backup the drive:

dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c > /path/to/backup.img.gz

If necessary (e.g. when the format of the external HD is FAT32) split the disk image in volumes (see also the split man pages):

dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c | split -a3 -b2G - /path/to/backup.img.gz

If there is not enough disk space locally, you may send the image through ssh:

dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c | ssh user@local dd of=backup.img.gz

Finally, save extra information about the drive geometry necessary in order to interpret the partition table stored within the image. The most important of which is the cylinder size.

fdisk -l /dev/sda > /path/to/list_fdisk.info

Note: You may wish to use a block size (bs=) that is equal to the amount of cache on the HD you are backing up. For example, bs=8192K works for an 8 MiB cache. The 64 KiB mentioned in this article is better than the default bs=512 bytes, but it will run faster with a larger bs=.

Restore system

To restore your system:

gunzip -c /path/to/backup.img.gz | dd of=/dev/sda

When the image has been split, use the following instead:

cat /path/to/backup.img.gz* | gunzip -c | dd of=/dev/sda

How to create a temporary ftp server

Using pyftpdlib:

pip3 install --user pyftpdlib
python3 -m pyftpdlib --port=2121 --write --username=user --password=password

This will create an FTP server listening on port 2121 accepting connections that can write into the current directory.

Group AWS ECR images

With the help of https://github.com/stedolan/jq/issues/274#issuecomment-64925860

aws ecr list-images --repository-name ${repository_name} | jq '.[] | group_by(.imageDigest) | map({"digest": .[0].imageDigest, "tags": map(.imageTag)})'

This will display all the tags associated with the image digest.

xorg - List all valid kbd layouts, variants and toggle options (to use with setxkbmap):

    Take a look at localectl, especially following options:

    localectl list-x11-keymap-layouts - gives you layouts (~100 on modern systems)
    localectl list-x11-keymap-variants de - gives you variants for this layout (or all variants if no layout specified, ~300 on modern systems)
    localectl list-x11-keymap-options | grep grp: - gives you all layout switching options

Onde logs estão localizados no Linux

Logs de ssh

  • /var/log/auth.log
  • /var/log/secure
  • journalctl -u sshd | tail -100

Simple monitoring with gkrellm

On the remote (to be monitored computer):

sudo sh -c 'apt-get update && apt-get install -y gkrellmd'

On your local machine, create an SSH tunnel to the remote machine:

ssh -N -f -L 19151:127.0.0.1:19150 user@remote_machine_ip

Open gkrellm on your machine listening to the local port that will receive information:

gkrellm -s 127.0.0.1 -P 19151

Help from https://totallynoob.com/server-monitoring-remote-monitor-a-server-with-gkrellm-via-ssh-tunnel/

Limiting the bandwith for a program

trickle -s -d 100 -u 100 <program>

Uses trickle to limit the bandwith that will be used by a program.

Discover other machines on your network

Grab your IP with a ifconfig then later use a nmap to scan your network, something like:

sudo nmap -sP 10.253.0.0/16

Updating the DNS being used

Check which DNS you are using:

nslookup google.com

It is using the IPs that appear on Server and Address. To change it:

Add

nameserver 8.8.8.8
nameserver 1.1.1.1

to /etc/resolvconf/resolv.conf.d/head and

sudo resolvconf -u

Validate that the DNS has been updated:

nslookup google.com

Thanks to https://www.linuxquestions.org/questions/linux-networking-3/how-to-change-the-dns-server-in-linux-mint-and-should-i-4175597949/#post5658301

Installing

sudo apt-get install -y pass

Do not forget to configure the completion for your preferred shell.

Before using it

Before using pass we need to have a key generated by GnuPG with:

gpg2 --gen-key

As it may take a lot of time, specially for it to gather enough entropy, one can use this solution from StackOverflow:

Anytime I've seen it (gpg --gen-key) hang like this, I log in to another shell and start a "dd if=/dev/sda of=/dev/zero" and it takes off after a few seconds / minutes.

By my experience, even using this method it still took around 10 minutes for the key generation.

Exporting Keys

If you need to export your keys to another machine one can follow the commands that are described in this StackOverflow question.

$ gpg --export-secret-keys > keyfile
$ gpg2 --import keyfile

Here they explicitly use different versions of GnuPG as the new versions of pass use gpg2.

Setting up

According to the official site tutorial and the extended git example we can start using it like this:

  • List your current available keys

    gpg2 --list-key

  • And use one of those keys with pass

    pass init key@mail

    pass git init

  • All files will be saved on ~/.password-store directory

  • If you have somewhere to push your passwords

    pass git remote add origin the-place-you-will-push-to:branch

  • Start inserting or generating your passwords

    pass generate A/B/mail@place.com 21 pass insert A/B/mail@place.com

  • When you are finished saving your passwords push them

    pass git push -u --all

More information on how to use pass can be found on its page and reading the man page.

Reaffirming trust

If you receive some error like this one after reimporting your key

gpg: <KEY>: There is no assurance this key belongs to the named user
gpg: [stdin]: encryption failed: Unusable public key

you can do as suggest on this StackOverflow thread and do a

gpg2 --edit-key <KEY>
gpg> trust
# Answer that you trust ultimately (5)
# Answer yes

Reduce size of PDF files

Low quality options:

gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -sOutputFile=new_file.pdf original_file.pdf
gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -sOutputFile=new_file.pdf original_file.pdf

The best balance was found in:

gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/default -sOutputFile=new_file.pdf original_file.pdf

Note: You may need to issue the command with a backslash in front of it if you use 'gs' as an alias:

\gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/default -sOutputFile=new_file.pdf original_file.pdf

Splitting and merging PDF files

With hints from:

Splitting

You can specify page ranges like this:

pdftk myoldfile.pdf cat 1-2 4-5 output mynewfile.pdf

pdftk has a few more tricks in its back pocket. For example, you can specify a burst operation to split each page in the input file into a separate output file.

pdftk myoldfile.pdf burst

By default, the output files are named pg_0001.pdf, pg_0002.pdf, etc.

Merging

pdftk is also capable of merging multiple pdf files into one pdf.

pdftk pg_0001.pdf pg_0002.pdf pg_0004.pdf pg_0005.pdf output mynewfile.pdf

That would merge the files corresponding to the first, second, fourth and fifth pages into a single output pdf.

Joining/merging pdf pages/files into a single one

Install pdfjam from texlive-latex-recommended:

sudo apt-get install -y texlive-latex-recommended

Merge files with:

pdfjam Page1.pdf Page2.pdf --nup 2x1 --landscape --outfile Page1_2.pdf

Merge pages from the same file:

pdfjam file.pdf --nup 2x1 --landscape --outfile together.pdf

All this was possible with the help of https://superuser.com/questions/366490/how-to-merge-multiple-pdf-files-onto-one-page-with-pdftk/750293#750293

Join png files into single PDF

pdfjoin --a4paper --fitpaper false --rotateoversize false *.png

Or

convert *.png -compress jpeg -quality 50 result.pdf

Thanks to: https://stackoverflow.com/questions/4778635/merging-png-images-into-one-pdf-file

Convert PDFs into JPEGs

All pages into the same file

for i in *.pdf; do convert -density 600 -append $i ${i%.*}.jpg; done

With the help of linux - How to merge images in command line? - Stack Overflow

Printers Adventures on Linux

To make the Brother MFC-L2730DW work (I was only able to make it work on a LinuxMint 18.3 Virtual Machine, couldn't make it work on 20)

Basically you have to download the drivers only the "Driver install tool is enough" and follow the recommendations from How to Make a Brother Printer and Scanner Work in Ubuntu and update the /lib/udev/rules.d/60-libsane1.rules file with:

ATTRS{idVendor}=="04f9", ATTRS{idProduct}=="0439", ENV{libsane_matched}="yes"

Copy Paste of How to Make a Brother Printer and Scanner Work in Ubuntu:

EDIT 2020-06-19
Long time no edit!  My instructions below still mostly work it seems (which is bad on Brother for not making this more simple – fail, fail fail)

I wanted to add a quick note for 18.04 generation Ubuntu friends to consider as you are working through my nasty old messy post below:

First, if you are installing a network scanner / printer and you get the question “Select the number of destination Device URI” question, I just type the number 14 (A): Auto. option at the bottom.  Seems to work…

Then, be ready to provide your printers IP address.  If you didn’t know you can usually grab this from your router admin settings (I find this easier) or you can find it by pushing some buttons on the printer itself but I recall this was annoying… in either case you will need to punch in the ip address of the printer during setup so have it ready.

For the ‘libsane udev’ stuff below, the file has seemingly changed in recent ubuntu.  It now seems to be

60-libsane1.rules

Hope these updates help!

———————————–

*THIS WILL UNDERGO SOME EDITS BETWEEN OCT 31st and Nov 4th, 2016.  If you can get some answers below, great, but hopefully next week it will be more clear and helpful to more models of printers.

*Make sure to read my edits below this before starting as some things have changed…

*many edits below!  don’t start till you’ve skimmed them all

*PRE-note: if you can buy HP it’s probably better for you.  If you like pain like me, or already have pain, read on.

For some reason Brother printers are kind of hard to make work in Ubuntu for me.  Especially the scanner part.  They claim to support ‘linux’ but it’s not typically plug in play for me.  However, they are ghetto cheap so I buy them and pay for the savings in set up pain.  Oh well.  But this time I’m wising up and I’m blogging this for myself (and mom) so that we can get it set up quicker when we do upgrades or machine changes.  The main issue always seems to be this:

    Install the drivers with the command line as per the ‘pretty decent’ generic software from Brother found here: LINK TO UBUNTU BROTHER PRINTER DRIVERS
    select ‘linux’select ‘Linux (deb’)’Choose ‘driver install tool’ if you can which gets both the printer and the scanner going.’Agree to the EULA and Download’

    save file.  it will go to your ‘downloads’ folder if you have not told your browser to download it somewhere else.  You will need to know this for the next part so take a moment after the download to confirm it downloaded and you know where it is.
    follow instructions that appear on brother site right after downloading drivers, but here they are as of today (make sure on their site it’s up to date and don’t fully trust mine).Step1. Download the tool.(linux-brprinter-installer-*.*.*-*.gz)The tool will be downloaded into the default “Download” directory.
    (The directory location varies depending on your Linux distribution.)
    e.g. /home/(LoginName)/Download

    Step2. Open a terminal window and go to the directory you downloaded the file to in the last step.

    Step3. Enter this command to extract the downloaded file:

    Command: gunzip linux-brprinter-installer-*.*.*-*.gz

    Step4. Get superuser authorization with the “su” command or “sudo su” command.

    Step5. Run the tool:

    Command: bash linux-brprinter-installer-*.*.*-* Brother machine name

    Step6. The driver installation will start. Follow the installation screen directions.


     When you see the message “Will you specify the DeviceURI ?”,

     For USB Users: Choose N(No)
     For Network Users: Choose Y(Yes) and DeviceURI.

    The install process may take some time. Please wait until it is complete.
    Do this:
    1. Open “/lib/udev/rules.d/40-libsane.rules” file with ‘sudo nano’ command
    2.  Add the following two lines to the end of the device list. (Before the line “# The following rule will disable …”):
    Copy to your computer memory this:
    # Brother scanners
    ATTRS{idVendor}==”04f9″, ENV{libsane_matched}=”yes”   <–Paste it in with the special ‘control+shift+v’ (don’t use just regular control+v) feature in terminal

    Reboot the machine (you can just type sudo reboot if you are still in terminal and want it done fast…)
    open simple scan software from dash and try a test scan

For me, without doing step #2 above the printer will usually work but not the scanner.

Which makes me wonder if there is really any Ubuntu support at all…

But my ghetto printer/scanner is doing its job so oh well.

Hope this helps!

Displaying a function definition

If you have a bash defined funcion, e.g. foobar, and want to display its definition you can:

type foobar To discover its location declare -f foobar To display its definition

Found this info at Can bash show a function's definition? - Stack Overflow.

Bang commands

Description
!! Will execute the last command. Same as !-1 or "up-arrow + return". The most common use is sudo !! when issued command failed due to insufficient privileges.
!n Will execute the line n of the history record. In most cases using mouse is a better deal
!-n Will execute the command n lines back. You usually remember the last three-four command you issues so !-2 and !-3 speed things up.
!gzip will re-execute the most recent gzip command (history is searched in reverse order). String specified is considered to be the prefix of the command.
!?etc.gz same as above but the unique string doesn't have to be at the start of the command. That means that you can identify command by a unique string appearing anywhere in the command (might be faster then Ctrl-R mechanism)
!!:1 designates the first argument of the last command. This can be shortened to !1.
!!:$ designates the last argument of the preceding command. This may be shortened to !$.

I think you need you need to know five major bang commands (!!, !!:h, !!:f, !$, !1)

Useful idioms

Description
sudo !! reexecute the last command with prefix sudo.
cd !$ cd to the directory which is the last argument of the previous command.

Retrieving previous command arguments

Description
!:0 is the previous command name
!^, !:2, !:3, …, !$ are the arguments of the previous command
!* is all the arguments
!$ is the last argument. You can also use $_ to get the last argument of the previous command.

Lines in history

Description
!-1 previous command
!-2, !-3, ... are earlier commands and arguments can be extracted from earlier commands too
!-2^, !-2:2, !-2$, !-2* you can extract particular arguments as well.

Word designators

Generally a colon (:) separates the event designator and the word designator, but it can be omitted, if the word designator begins with $, %, ^, *, or - . As well for for command line arguments from 1 to 9 ($1-$9)

Description
0 the zero’th word (command name)
n word n
ˆ the first argument, i.e., word one (usually first argument of the command)
$ the last argument
% the word matched by the most recent
!? str ? search of str
x-y words x through y . −y is short for 0−y
* words 1 through the last (like 1−$ ) (all arguments)
n* words n through the last (like n−$ )

Modifiers:

Description
h remove the part of a filename after last "/", leaving the path
t remove all but the part of the filename after the last slash. for example for "/etc/resolv.conf" it will be resolv.conf
r remove the last suffix of a filename (extension of the file). For example /etc/resolv
e remove all but the last suffix of a filename (extension)
g make changes globally, use with s modifier, below
p print the command but do not execute it
q quote the generated text
s/old/new/ substitute new for old in the text. Any delimiter may be used. An & in the argument means the value of old. With empty old , use last old , or the most recent !? str ? search if there was no previous old
x quote the generated text, but break into words at blanks and newline
& repeat the last substitution

Example:

echo this is a phrase
!:s/this/that<tab>

Send command to all panes

prefix :set-window-option synchronize-panes on|off

On a default configuration:

ctrl-b :set-window-option synchronize-panes on

Credits to: tmux send command to all panes

How to upgrade python version

This is one way of compiling Python code and have it working on your system (Debian based)

Always visit Download Python | Python.org to check the newest releases of Python.

#!/usr/bin/env bash

python_version=3.7.2

sudo apt-get update
sudo apt-get -y install \
  build-essential \
  checkinstall \
  libbz2-dev \
  libc6-dev \
  libffi-dev \
  libgdbm-dev \
  libncursesw5-dev \
  libreadline-gplv2-dev \
  libsqlite3-dev \
  libssl-dev \
  tk-dev

cd /usr/src
sudo wget https://www.python.org/ftp/python/${python_version}/Python-${python_version}.tgz
sudo tar xzf Python-${python_version}.tgz
cd Python-${python_version}
sudo ./configure --enable-optimizations
sudo make -j 4 altinstall

cd ~/

# Just being sure that the new version is installed
python3.7 -V

# If we check the current alternatives it will break
# update-alternatives --list python3

# One can always add other alternatives
sudo update-alternatives --install /usr/bin/python3 python3 /usr/local/bin/python3.7 1

# Just showing off that things are working now
namei "$(which python3)"
python3 -V
/usr/bin/env python3 -V

After executing this process, pip failed because it could not find lsb_release, creating a symbolic link solved this issue:

sudo ln -s /usr/share/pyshared/lsb_release.py /usr/local/lib/python3.7/site-packages/lsb_release.py

Possible with the help of:

Wifi after hibernation

Change /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf to be:

[connection]
wifi.powersave = 2

Don't know if it really helped anything, but at least now I know that I have wifi after hibernation.

Download a video from youtube

To download a video from youtube:

youtube-dl --list-formats $youtube_link

After seeing the list of options and formats

youtube-dl -f $format $youtube_link

e.g. for download only the audio:

youtube-dl -f 140 $youtube_link

Convert the downloaded audio

When you download the audio it have an m4a extension, to convert to a mp3 audio file:

ffmpeg -i $m4a_file -acodec libmp3lame -ab 128k ${m4a_file%.*}.mp3

To to a batch conversion, and have safe names:

for file in *m4a; do rename 's/ /_/g' $file; done && for file in *m4a; do ffmpeg -i $file -acodec libmp3lame -ab 128k ${file%.*}.mp3; done

Create a ramdisk

mkdir -p /mnt/ramdisk && mount -t tmpfs tmpfs /mnt/ramdisk -o size=8192M

Get your current IPs

curl ifconfig.me

curl ipinfo.io/ip

Resetting the gpg-agent

If, by any reason, gpg stops working you can kill it:

gconf --kill gpg-agent

GPG will restart next time it is needed.

Tip from https://superuser.com/a/1150399

VirtualBox shared folder

If you are having permission denied issues on VirtualBox shared folders:

sudo usermod -aG vboxsf $(whoami)