Memo - Shell

This is one of my memos about shell commands.

Memos are used for recording the problems I encountered during programming and its solutions. I also write down something that is hard to remember for myself.

shell十三问 asciinema - recording terminal sessions and sharing them on the web

Command operators & separators

Shell - Multiple commands in one line

Daemon

nohup PROGRAM > /dev/null &

Tree

# List directories only
tree . -d
#   -L  level
#       Max display depth of the directory tree.
tree . -d -L 2

System and hardware information

Linux Version

Linux Command: bashow Linux Version

# Linux kernel version
uname -r
# or
cat /proc/sys/kernel/{ostype,osrelease,version}

# Linux distribution version
lsb_relase -a
cat /etc/*release*

Hardware Information

# A very colorful system summary
neofetch
# cpu and processing units
lscpu
# list block devices 
lsblk
# disk space of file systems
df -H
# memory
free -h
# usb
lsusb
# nvidia gpu
nvidia-smi

System Resources

htop

# Dynamic monitor gpu (nvidia only)
watch -n 0.1 nvidia-smi
# kill process with fully command
pkill -f "process with arguments"
# Find process that listening specific port
sudo lsof -n -P -i :80

SSH

# Generate SSH key & add it to ssh agent
#   https://gist.github.com/jexchan/2351996
eval `ssh-agent`
ssh-keygen -t rsa -C "your_email@youremail.com" -f filename
ssh-add filename
ssh-add -l
# Enable trusted x11 forwarding
#   -Y      Enables trusted X11 forwarding.  
#           Trusted X11 forwardings are not subjected to 
#           the X11 SECURITY extension controls.
#   ( man ssh )
ssh NAME@HOST -p PORT -Y

# Port forwarding
#   This will forward FORWARD_HOST:FORWARD_PORT to localhost:LOCAL_PORT
#   via ssh NAME@HOST -p PORT
#   ( if you want to bind HOST:PORT with localhost:LOCAL_PORT,
#       just set FORWARD_HOST to 0.0.0.0
#       instead of setting FORWARD_HOST equal with HOST )
#   -L [bind_address:]port:host:hostport
#   -L [bind_address:]port:remote_socket
#   -L local_socket:host:hostport
#   -L local_socket:remote_socket
#   -N Do not execute a remote command (specific for port forwarding). Use this will not open a remote shell for you.
#   -f Go background
# Example: ssh -L 3000:mysql.server.com:3306 root@aliyun.com
#   mysql.server.com can only accessed by the machine whose hostname is aliyun.com
#   Notice: mysql.server.com is not deployed in the aliyun.com
#   This will forward mysql.server.com:3306 => localhost:3000
#   aliyun.com just like a bridge in this scenario
# Example: ssh -L 3000:0.0.0.0:3306 root@aliyun.com
#   This wiil forward aliyun.com:3306 => localhost:3000
# -f is optional
ssh -N -L -f LOCAL_PORT:FORWARD_HOST:FORWARD_PORT USERNAME@HOST -p PORT

# Authorized with keys
#   Clinet side: Add your public key to server
cat ~/.ssh/id_rsa.pub | ssh -p PORT NAME@HOST 'cat >> .ssh/authorized_keys'
#   Client side: Change the file mode on server ( important! )
cat ~/.ssh/id_rsa.pub | ssh -p PORT NAME@HOST 'mkdir .ssh; cat >> .ssh/authorized_keys'

Grammar

Associative array

Bash associative array examples

Read file

#!/bin/bash
# Read file line by line
input="/path/to/txt/file"
while IFS= read -r var
do
  echo "$var"
done < "$input"
# Read file line by line with IFS (internal field separator)
while IFS=, read -r v1 v2 v3
do
    echo "$v1: $v2, $v3"
done < "$input"