Linux

Inspect

File

# List files
ls -alh file

# Modify user group
chown -R alice file
chown -R alice:www-data file

# Modify perms
chmod 600 file
chmod -w file
chmod +x file
chmod o-x file
chmod u+w file

# Open with default app
xdg-open file

# link file
ln -s /user/bin/vim /usr/bin/vi
# Link file relative
ln -sr node_modules/eslint/bin/eslint.js node_modules/.bin/eslint

# Zip
zip -r data.zip data
# Inspect zip files
unzip -t data.zip
# Unzip file
unzip data.zip
# Unzip to specific folder
unzip -d output-dir data.zip
# Unzip with pass
zip -er data.zip data

# Tar
tar -cf data.tar.gz data
# Inspect tar files
tar -tf data.tar.gz
# Untar
tar -xf data.tar.gz
# Untar to specific folders
tar -xf data.tar.gz -C output-dir

# bz format compression (slower but smaller)
tar -cjf data.tar.bz2 data

# Download
wget $url
wget -O /tmp/file $curl
curl -o /tmp/file $curl

# Find
find -name README.md
find / -name sfz
find -type -f -name '*.log' -exec rm -rf {} \;

# split by number of copies
split -d -n 5 data.zip data.zip.part
# split by size
split -d -b 256M data.zip data.zip.part
# Combine split files
cat data.zip.part* > data.zip

# generate file
dd if=/dev/zero of=/tmp/1G.bin bs=1M count=1000
dd if=/dev/urandom of=/tmp/1G.bin bs=10M count=1000

User/Group

# add users (more complete, similar to interface operations)
adduser alice
# add user (recommended version)
useradd -m alice
# add user, specify user directory
useradd -d /d/alice alice
# add user, specify uid, gid
useradd -u 1001 -g 1001 nodejs
# add program account
useradd -r -s /usr/sbin/nologin nodejs

# MODIFY THE USER SHELL
usermod -s /usr/bin/bash alice

# user join group
usermod -a -G docker alice

# modify user password
passwd alice

# delete users
userdel nodejs

# add group
groupadd -g 344 linuxde
# delete group
groupdel linuxde

Process

# find process
ps aux | grep nginx

# kill process
kill $pid
# kill process forcelly
kill -9 $pid
# kill process by name
pkill nginx
pkill '^ssh$'
pkill -9 nginx

# find process by port
lsof -i:3000
netstat -utlpn | grep 3000
# find port by process
netstat -utlpn | grep nginx

cat /proc/$pid/status | grep VmRSS
cat /proc/$pid/cmdline 
cat /proc/$pid/environ 

ls -l /proc/$pid/cwd
ls -l /proc/$pid/exe
ls -l /proc/$pid/root

# run in backgroud
nohup server &
nohup server > server.log 2>&1 &
nohup server > server.log 2> server.err &

Text

# count lines
cat file | wc -l

# first n lines
cat file | head -3
# last n lists
cat file | tail -3

cat file | more

# hex
cat file | xxd 
cat file | xxd -p > file.hex

# split columns with `:`, only show first, third columns
cat /etc/group | cut -d: -f1,3
# only show 5-10 charactors of each row
cat file | cut -c5-10
# only show first 10 charactors of each row
cat file | cut -c-10
# only show 10th and subsequent of each line
cat file | cut -c10-

# replace charactor
cat file | tr '\t' ' '
# delete charactor
cat file | tr -d '\r'

# remove duplicates
cat file | sort | uniq 
# count duplicates
cat file | sort | uniq -c
# show duplicates
cat file | sort | uniq -d

sed

# delete first line
cat file | sed '1d'
# delete empty line
cat file | sed '/^$/d'
# insert at first line
cat file | sed '1i#!/usr/bin/env node\n'
# append on last line
cat file | sed '$a\\n'
# replace functions
cat file | sed '/foo() {/,/}/c foo() { }'
# replace path
cat file| sed 's|/bin/sh|/bin/bash|g'
# replace with matched parts
cat file | sed 's|\(\w\+\) \(\w\+\) \(\w\+\)|\2 \3 \1|'
# change file
sed -i 's/\w\+.ubuntu.com/mirrors.tuna.tsinghua.edu.cn/' /etc/apt/sources.list

awk

# print specific column
docker images | awk '{print $1}'
# specific delimeter
cat /etc/paswd | awk -F: '{print $1}'
# combine columns
cat file | awk '{print $1,$3}'

Regex

GLOB

Terminal

• !! last command
• !$ last postional parameter of last command

Set

set -euxo pipefail

• -e: Exit on none-zero status
• -x: Print a trace
• -u: Treat unset variables as error
• -o pipefail: Return none-zero if last pipeline return none-zero

Xargs

Capture the output of one command and pass it to another command

# Batch renames
ls -1 . | sed 's/\.mdx$//' | xargs -I{} mv {}.mdx {}.md

Cron Syntax

Min  Hour Day  Mon  Weekday
*    *    *    *    *  command to be executed
┬    ┬    ┬    ┬    ┬
│    │    │    │    └─  Weekday  (0=Sun .. 6=Sat)
│    │    │    └──────  Month    (1..12)
│    │    └───────────  Day      (1..31)
│    └────────────────  Hour     (0..23)
└─────────────────────  Minute   (0..59)

Common Snippets

Script Directory

SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )"

Sudo Without Pass

cat << EOF | sudo tee -a /etc/sudoers.d/$USER
$USER ALL=(ALL) NOPASSWD:ALL
EOF 

Ulimit

cat <<EOF | sudo tee -a /etc/security/limits.d/$USER.conf
$USER soft nproc 100000
$USER hard nproc 100000
$USER soft nofile 100000
$USER hard nofile 100000
EOF

Change repo source

ubuntu

sed -i -E 's/\w+.ubuntu.com/mirrors.tuna.tsinghua.edu.cn/g' /etc/apt/sources.list

Alpine

sed -i 's/dl-cdn.alpinelinux.org/mirrors.tuna.tsinghua.edu.cn/g' /etc/apk/repositories

Load environment variables from .env

eval $(cat .env | sed 's/^/export /')