Code Sniffer

First Check if phpcs is installed or not

which phpcs
It should return path of current phpcs installation.
If returned nothing probably phpcs is not installed.

phpcs --version
To check which version you're using. Always try to get latest version. Head out to https://github.com/squizlabs/PHP_CodeSniffer/releases to check latest version.

Install or update.

Depends on method you've installed phpcs you need to update.

Composer install or update.

Assuming you have php and composer pre installed.

Go to composer dir cd ~/.composer

composer global require "squizlabs/php_codesniffer=*"

composer update squizlabs/php_codesniffer to update if you already have installed.

Then you can check version by doing ./vendor/bin/phpcs --version
Add ~/.composer/vendor/bin to $PATH in .bashrc or .zshrc and reload terminal or open new tab.

Or Direct download

curl -OL https://squizlabs.github.io/PHP_CodeSniffer/phpcs.phar && chmod +x phpcs.phar && mv phpcs.phar /usr/local/bin/phpcs
curl -OL https://squizlabs.github.io/PHP_CodeSniffer/phpcbf.phar && chmod +x phpcbf.phar && mv phpcbf.phar /usr/local/bin/phpcbf

/usr/local/bin/ You can change this to custom path like ~/.bin and add that custom path to $PATH as mentioned above in composer install section.

Install WPCS and PHPCompatibility

Direct download

You can install WPCS and VIP Coding Standards via git repo as mentioned below.

cd ~/Documents
mkdir Coding-Standards && cd $_
git clone -b master https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards.git wpcs
git clone -b master https://github.com/Automattic/VIP-Coding-Standards.git
git clone -b master https://github.com/wimg/PHPCompatibility.git PHPCompatibility
pwd # copy this
ln -s {paste here}/PHPCompatibility/PHPCompatibility wpcs/PHPCompatibility
ln -s {paste here}/VIP-Coding-Standards/WordPressVIPMinimum wpcs/WordPressVIPMinimum
phpcs --config-set installed_paths {Paste here again}/wpcs # remember this path

via composer

You can install it via composer using following.

composer global require dealerdirect/phpcodesniffer-composer-installer \
    wp-coding-standards/wpcs 1.2.1 \
    automattic/vipwpcs \
    phpcompatibility/php-compatibility \
    phpcompatibility/phpcompatibility-wp:* --update-no-dev

Note: you won't need to set installed_paths when used with composer as dealerdirect/phpcodesniffer-composer-installer will take care of it.

You should checkout each github repo for coding standard and see it's purpose.

Check and Fix phpcs path

Try phpcs -i it should show WordPress, PHPCompatibility, WordPress-Extra, WordPress-Docs, WordPress-Core ruleset there.

If somehow it doesn't show you, you need to exec last command phpcs --config-set... again. (you should do this everywhere you update phpcs)

Update WPCS and PHPCompatibility

phpcs --config-show

Copy path given in installed_paths. If you don't get that path check above section on how to fix that.

cd {Paste here}
git pull origin master 
cd PHPCompatibility
git pull origin master

Note: You should update wpcs every month or so or on every release.

Using phpcs

You should checkout https://github.com/squizlabs/PHP_CodeSniffer/wiki for usage.

You can run phpcs on single file using phpcs --standards=wordpress-core file/or/folder/path

Ideally each project should have phpcs.ruleset.xml with rules defined in it.

Sample configuration file: https://github.com/xwp/wp-foo-bar/blob/master/phpcs.ruleset.xml