/cli-tips-and-tricks

MIT LicenseMIT

CLI Tips and Tricks

A collection of useful command-line one-liners, scripts, and tips for Linux/Unix systems administration and development.

Contents

Benchmarking

Quick server benchmarking scripts.

Method 1:

wget -qO- bench.sh | bash

Method 2:

curl -Lso- bench.sh | bash

⚠️ Security Note: Always review scripts before piping to bash. Consider running without | bash first to inspect the content.

User Management

Allow superuser access without password

Option 1: Add to main sudoers file

echo "$USER ALL=(ALL) NOPASSWD: ALL" | sudo tee -a /etc/sudoers

Option 2: Create user-specific sudoers file (recommended)

For Debian:

echo 'debian ALL=(ALL) NOPASSWD:ALL' | sudo tee /etc/sudoers.d/debian

For Ubuntu:

echo 'ubuntu ALL=(ALL) NOPASSWD:ALL' | sudo tee /etc/sudoers.d/ubuntu

For CentOS/RHEL:

echo 'centos ALL=(ALL) NOPASSWD:ALL' | sudo tee /etc/sudoers.d/centos

⚠️ Security Warning: NOPASSWD is convenient but reduces security. Use only for development/testing environments.

Colored Bash Prompts

Useful for distinguishing root from regular users.

Regular user (green prompt):

echo "PS1='\[\e[1;32m\][\u@\h \W]\$\[\e[0m\] '" >> ~/.bashrc

Root user (red prompt):

echo "PS1='\[\e[1;31m\][\u@\h \W]\$\[\e[0m\] '" >> ~/.bashrc

Apply changes:

source ~/.bashrc

System Configuration

Dropbox inotify fix

Increase the inotify watch limit:

echo fs.inotify.max_user_watches=100000 | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

Date and Time

Useful date formatting for timestamps.

Basic date format (YYYYMMDD):

date +"%Y%m%d"

Example output: 20131016

ISO date format (YYYY-MM-DD):

date +"%Y-%m-%d"

Example output: 2013-10-16

Full timestamp (YYYYMMDD_HHMMSS):

date +"%Y%m%d_%H%M%S"

Example output: 20131016_193655

Pastebin Services

Termbin

Quick text sharing via netcat.

Pipe any output to termbin:

ls -la | nc termbin.com 9999

Website: http://termbin.com/

Paste.rs

Modern Rust-based pastebin service.

Pipe to paste.rs:

echo "Hello World" | curl --data-binary @- https://paste.rs

From file:

curl --data-binary @file.txt https://paste.rs

Website: https://paste.rs

ix.io

Simple pastebin via curl.

Pipe any output:

ls -la | curl -F 'f:1=<-' ix.io

From file:

curl -F 'f:1=<-' ix.io < file.txt

Docker

Installation

Modern method (recommended):

Ubuntu/Debian:

sudo apt-get update
sudo apt-get install docker.io docker-compose

RHEL/CentOS/Fedora:

sudo dnf install docker docker-compose

Arch Linux:

sudo pacman -S docker docker-compose

Quick install script (for supported distros):

curl -fsSL https://get.docker.com | sudo sh

⚠️ Note: Always review scripts before piping to shell.

Allow non-root usage

Add current user to docker group:

sudo usermod -aG docker $USER

Add specific user (e.g., ubuntu):

sudo usermod -aG docker ubuntu

Apply group changes (or logout/login):

newgrp docker

Container IP addresses

Get IP of specific container (by ID):

docker inspect --format '{{ .NetworkSettings.IPAddress }}' ${CID}

Get IP of specific container (by name):

docker inspect --format '{{ .NetworkSettings.IPAddress }}' container_name

Get IPs of all running containers:

docker inspect --format '{{ .Name }} - {{ .NetworkSettings.IPAddress }}' $(docker ps -q)

Using jq for JSON parsing:

docker inspect container_name | jq -r '.[0].NetworkSettings.IPAddress'

AWK

Powerful text processing examples.

Print the first statement on first line:

cat file | awk 'NR==1{print $1}'

Print assigned IP addresses on network interface:

arp -n | grep eth0 | awk '{print $1}'

Print all columns:

awk '{print $0}' file

Print the 3rd column:

awk '{print $3}' file

Print the 1st and 3rd columns:

awk '{print $1 $3}' file

Print all columns except the 3rd:

awk '{$3=""; print $0}' file

Print all columns except the 1st and 2nd:

awk '{$1=$2=""; print $0}' file

Find

Change permissions

For directories:

find . -type d -exec chmod 755 {} +

For files:

find . -type f -exec chmod 644 {} +

SSH directory example:

find $HOME/.ssh/ -type f -exec chmod 600 {} +

Change ownership

sudo find . -type d -user root -exec chown idv:idv {} \;

Make scripts executable

find . -name "*.sh" -execdir chmod u+x {} +

Find largest files

du -hsx * | sort -rh | head -10

Sed

Common replacements

Disable GRUB boot animation:

Ubuntu/Debian:

sudo sed -i 's/quiet splash//' /etc/default/grub && sudo update-grub

RHEL/CentOS/Fedora:

sudo sed -i 's/quiet splash//' /etc/default/grub && sudo grub2-mkconfig -o /boot/grub2/grub.cfg

Locale correction:

sed -i 's/uk_UA.UTF-8/en_US.UTF-8/' /etc/default/locale

Replace hostname in /etc/hosts:

sed -i "s/ubuntu1404/$(hostname)/" /etc/hosts

Text replacement in multiple files

Method 1: Using grep and xargs

grep -rl "windows" . | xargs sed -i "s/windows/linux/g"

Method 2: Using find

find /path -type f -exec sed -i 's/example.com/superexample.com/g' {} +

💡 Tip: Use sed -i.bak to create backups before replacing.

Network Tools

ifconfig.me / ifconfig.co

Get external IP:

curl ifconfig.co

Get all network information:

curl ifconfig.co/all

Alternative services:

curl ifconfig.me
curl icanhazip.com
curl ipinfo.io/ip

SSH

Fix authentication agent error

Modern syntax (preferred):

eval "$(ssh-agent -s)"

Check agent socket:

echo $SSH_AUTH_SOCK

Legacy syntax (still works):

eval `ssh-agent`

Add SSH keys to agent

Add default key:

ssh-add

Add specific key:

ssh-add ~/.ssh/id_ed25519

List loaded keys:

ssh-add -l

SSH Port Forwarding

Local port forward syntax:

ssh -L <local_port>:<destination_server>:<destination_port> user@<ssh_server> -p <ssh_port>

Example: Access router's web interface

If router's WAN IP is 12.23.34.45, SSH port is 9999, and web interface is on port 80:

ssh -L 12345:localhost:80 root@12.23.34.45 -p 9999

Then access via: http://localhost:12345

Multiple port forwards:

ssh -L 8080:127.0.0.1:80 \
    -L 8443:127.0.0.1:443 \
    -L 8001:127.0.0.1:8001 \
    -L 5901:127.0.0.1:5901 \
    -L 1313:127.0.0.1:1313 \
    user@host

Bash Loops

Simple numeric range

for i in {1..10}; do command; done

Specific numbers

for i in {18,20,21}; do
    sleep 10
    ssh node-$i "tar zcvf - /var/log/ceilometer | cat > /tmp/ceilometer-node$i.tar.gz"
done

Copy files from multiple nodes

for i in {18,20,21}; do
    scp node-$i:/tmp/ceilometer-node$i.tar.gz .
done

Archive Handling

Download and extract archives in one command.

Using wget

Uncompressed tar:

wget http://example.com/archive.tar -O - | tar -x

Gzipped tar:

wget http://example.com/archive.tar.gz -O - | tar -xz

Bzip2 tar:

wget http://example.com/archive.tar.bz2 -O - | tar -xj

Using curl

Uncompressed tar:

curl http://example.com/archive.tar | tar -x

Gzipped tar:

curl http://example.com/archive.tar.gz | tar -xz

Bzip2 tar:

curl http://example.com/archive.tar.bz2 | tar -xj

Vim/Neovim Plugin Management

Pathogen (Legacy)

Install Pathogen plugins from file (if you have a plugins file listing GitHub repositories):

while read plugin; do
    git clone https://github.com/$plugin ~/.vim/bundle/
done < plugins

Modern Alternatives

vim-plug (most popular):

Add to ~/.vimrc:

call plug#begin()
Plug 'tpope/vim-sensible'
Plug 'junegunn/fzf'
call plug#end()

Native package management (Vim 8+):

git clone https://github.com/tpope/vim-sensible.git \
    ~/.vim/pack/vendor/start/vim-sensible

Neovim with lazy.nvim: Modern Lua-based plugin manager for Neovim users.

Cat with Heredoc

Multiline string to variable

sql=$(cat <<EOF
SELECT foo, bar FROM db
WHERE foo='baz'
EOF
)

Check the variable:

echo -e "$sql"

Multiline string to file

cat <<EOF > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
EOF

The print.sh file will contain:

#!/bin/bash
echo $PWD
echo /home/user

Multiline string to command/pipe

cat <<EOF | grep 'b' | tee b.txt | grep 'r'
foo
bar
baz
EOF

This creates b.txt with both bar and baz lines but prints only bar.

Contributing

Feel free to submit pull requests with additional tips and tricks!

License

MIT License - feel free to use these commands in your own work.