cheatsheet

Just another nasty cheatsheet.

• Docker
• Git
• Node.js
• MySQL
• Shell scripting
• SSH
• Compression
• Image processing
• Scraping
• macOS
• Windows

Docker

Copy folder between Docker container and host

# Docker container -> Host
docker cp container_name:/srv/public/content/uploads ~/Downloads/uploads
# Host -> Docker container
docker cp ~/Downloads/uploads container_name:/srv/public/content/uploads

Import and export MySQL database dumps

# Export or dump database
sudo docker exec -i container_name bash -c 'mysqldump -u $DB_USER -p"$DB_PASS" --default-character-set=utf8mb4 $DB_NAME' > /path/to/$(date +%F)-database.sql
# Import database (Attention!)
sudo docker exec -i container_name bash -c 'mysql -u $DB_USER -p"$DB_PASS" --default-character-set=utf8mb4 $DB_NAME' < /path/to/$(date +%F)-database.sql

Git

Change remotes

# List remotes
git remote -v
# Add an 'origin' remote
git remote add origin [email protected]:ffraenz/macos-config.git
# Change the 'origin' remote's URL
git remote set-url origin [email protected]:ffraenz/macos-config.git
# Remove the 'origin' remote
git remote rm origin

Change file name case

git mv -f readme.md README.md

Configure git

Remove the --global flag to only configure the current repository.

git config --global user.name "Example User"
git config --global user.email [email protected]
git config --global pull.rebase false
git config --global init.defaultBranch main
git config --global commit.gpgsign true
# Use the last 8 hex-formatted bytes from the fingerprint as signing key id
git config --global user.signingkey 583D205C93C01BC0

Fix “error: cannot run gpg”

git config --global gpg.program "$(which gpg)"

Create a file patch using diff

diff -Naur original_file_name changed_file_name > name.patch

Node.js

Fix global and n package permissions

sudo mkdir -p /usr/local/n
sudo chown -R $(whoami) /usr/local/n /usr/local/bin /usr/local/lib /usr/local/include /usr/local/share

MySQL

Clear a database

DROP DATABASE name;
CREATE DATABASE name;

Enable or disable general logging

Log every connection and every query that clients send to the MySQL server.

SET GLOBAL general_log = 'ON';
SET GLOBAL general_log = 'OFF';

Follow default MySQL log:

tail -f /var/log/mysql/mysql.log

Shell scripting

Shebang

In Unix, when a text file has a shebang, it is interpreted as an executable file.

#!/bin/sh
#!/bin/bash
#!/usr/bin/env python

Date and time

Common date command formats:

Description	Command	Output
Date	date +"%d.%m.%Y"	09.02.2020
Date (path safe)	date +%F	2020-02-09
Time	date +%T	21:23:52
Time (path safe)	date +"%H-%M-%S"	21-23-52
Local date and time	date +%c	Sun Feb 9 21:23:52 2020
Unix timestamp	date +%s	1581279832

Redirect shell script stdout & stderr to a log file

This command redirects the following stdout and stderr to both a log file and the stdout of the shell script.

exec 1> >(tee $LOG_PATH) 2>&1
echo "Hello, stdout." >&1
echo "Hello, stderr." >&2

Typical control flow structures

Common bash control flow structures:

Description	Structure
String $a equals $b	if [ $a = $b ]; then ... fi
String $a does not equal $b	if [ $a != $b ]; then ... fi
$string is empty -z / not empty -n	if [ -z $string ]; then ... fi
$path exists	if [ -e $path ]; then ... fi
$path is a file -f / directory -d	if [ -f $path ]; then ... fi
$path is readable -r / -w / -x by user	if [ -r $path ]; then ... fi
$a is newer -nt / older -ot than $b	if [ $a -nt $b ]; then ... fi
For loop over values	for i in 1 2 3 4 5; do ... done
For loop over files	for PATH in /foo/*; do ... done
For loop over directories	for PATH in /foo/*/; do ... done
While loop	while [ condition ]; do ... done

SSH

Create SSH public and private key pair

ssh-keygen -t rsa -b 4096 -f ~/.ssh/id_rsa -C "[email protected]"

Add public key to a host's authorized keys

ssh-copy-id -i ~/.ssh/id_rsa user@host

Defer public key from existing private key

ssh-keygen -y -f ~/.ssh/id_rsa > ~/.ssh/id_rsa.pub

Fix ~/.ssh permissions

chown -R $USER ~/.ssh
sudo chmod 700 ~/.ssh
sudo chmod 644 ~/.ssh/authorized_keys
sudo chmod 600 ~/.ssh/id_* ~/.ssh/config

Compression

Tar archive compression and extraction

Create an archive (-c) using gzip compression (-z) with the given filename (-f). Given the (-C) option tar changes into the given folder before compressing the target . preventing absolute URLs from showing up in the resulting archive.

COPYFILE_DISABLE=1 tar -zcf archive.tar.gz -C path/to/folder *

Extract a tar ball (-x) with the given filename (-f):

tar -xf archive.tar.gz

ZIP archive compression and extraction

Create an archive from a folder (-r) without invisible Mac resource files (-X).

zip -r -X archive.zip path/to/folder
zip archive.zip file1 file2 file3

Extract a ZIP archive into the same folder:

unzip archive.zip

Image processing

Create multi-resolution favicon

# Make prerequisites available
brew install imagemagick optipng

# Optimize source PNGs and generate ICO file
optipng -o7 *.png
convert favicon-*.png favicon.ico

Scraping

Scrape an entire website to create a local static copy of it:

wget -m -k -E -l 7 -t 3 -w 1 -e robots=off --reject "none*" http://example.com

macOS

Resolve code signing issues

Before working with a certiciate from the shell, make sure it is available in the Keychain Access GUI and is shown as valid. If it is not shown as valid, the root certificate may be missing from the Apple PKI, so import it if needed.

Now, make sure certificates are available to the shell by running the following command and checking if it appears in the 'Valid identities only' section.

security find-identity -p codesigning

To sign an app or dylib library, do the following:

cp /usr/bin/true MyTrue
codesign -s "Apple Development" -f MyTrue

Resources:

• Resolving errSecInternalComponent errors during code signing

Create a bootable macOS installer on macOS

See How to create a bootable installer for macOS.

Windows

Create a bootable Windows 10 installer on macOS

First download a Windows 10 ISO image from this Microsoft page. After that follow these steps:

# If not done yet, install wimlib to split files that are too big
brew install wimlib

# Identify the disk identifier (disk#)
diskutil list
# Erase and format disk
diskutil eraseDisk MS-DOS "WINDOWS10" MBR disk#
# Mount the ISO file - returning the mounted volume name
hdiutil mount ~/Downloads/Win10_XXXX_XX_English_x64.iso
# Copy supportive files excluding install.swm
rsync -avhP --exclude=sources/install.wim /Volumes/CCCOMA_ISO_VOLUME/ /Volumes/WINDOWS10/
# Copy splitted install.swm file
wimlib-imagex split /Volumes/CCCOMA_ISO_VOLUME/sources/install.wim /Volumes/WINDOWS10/sources/install.swm 4000
# Unmount disks, the ISO file is no longer needed
hdiutil unmount /Volumes/WINDOWS10/
hdiutil unmount /Volumes/CCCOMA_ISO_VOLUME/

Clean a disk

During Windows installation or when setting up a drive for the first use, you may need to clean or reset all partitions on a drive removing all data from it. For that open cmd and run diskpart, then type:

list disk
REM Identify the disk you want to reset
select disk #
REM Caution! The following command is dangerous.
clean
REM Check on the results
list disk

Tunnel Windows Remote Desktop (RDP) through SSH on Linux

When having an an on-premise Linux server to SSH into it is possible to tunnel an RDP connection through SSH port forwarding to remote control a Windows machine from a Mac located outside the network.

Establish port forwarding between the Mac and a remote Linux host:

ssh -N -L 13389:[Remote IP]:3389 host

Now connect with the RDP client to 127.0.0.1:13389 as if it were the remote server.