Steps:

Create a new pipeline in the root of the project with the file name bitbucket-pipelines.yml or if it exists add just the step and the trigger to the existed pipeline.

# These are yaml anchors, reused later
x-bash-env-steps:  
- &bash_env_export export BASH_ENV="$BITBUCKET_CLONE_DIR/.bashrc"  
- &bash_env_source source $BASH_ENV
# This is a larger yaml anchor, reused for each pipeline
pull_requests: &pull_requests  
- step:      
name: 'PHPCS'      
image: wodby/drupal-php:7.4      
script:        
- composer install        
- ./vendor/bin/phpcs -q --colors --standard=Drupal --extensions=php,module,inc,install,test,profile,theme ./web/modules/custom
- ./vendor/bin/phpcs -q --colors --standard=DrupalPractice --extensions=php,module,inc,install,test,profile,theme ./web/modules/custom        
- ./vendor/bin/phpcs -q --colors --standard=Drupal --extensions=php,module,inc,install,test,profile,theme --report=diff ./web/modules/custom        
- ./vendor/bin/phpcs -q --colors --standard=DrupalPractice --extensions=php,module,inc,install,test,profile,theme --report=diff ./web/modules/custom        
- ./vendor/bin/phpcs -q --colors --standard=Drupal --extensions=php,module,inc,install,test,profile,theme ./web/themes/custom  
- ./vendor/bin/phpcs -q --colors --standard=DrupalPractice --extensions=php,module,inc,install,test,profile,theme ./web/themes/custom        
- ./vendor/bin/phpcs -q --colors --standard=Drupal --extensions=php,module,inc,install,test,profile,theme --report=diff ./web/themes/custom        
- ./vendor/bin/phpcs -q --colors --standard=DrupalPractice --extensions=php,module,inc,install,test,profile,theme --report=diff ./web/themes/custom
options:  
max-time: 30
pipelines:  
pull-requests:    
# Using the custom pull_request pipeline on each pull request created.    
'**': *pull_requests