Run PHP code sniffer over the files that are about to be committed. Takes into account both PHP 5 and 7.

phpcs.xml

<?xml version="1.0"?>
<!-- Location: $HOME/config/phpcs.xml -->
<ruleset name="burhan">
    <rule ref="Squiz.Commenting.FunctionComment">
        <!-- excluded because they can't be used for both php 5 and 7 -->
        <!-- PHP 7 will make this complaint if scalar type hints (eg int) are missing -->
        <exclude name="Squiz.Commenting.FunctionComment.ScalarTypeHintMissing" />
        <!-- PHP 5 will make this complaint if scalar type hints (eg. int) exist -->
        <exclude name="Squiz.Commenting.FunctionComment.InvalidTypeHint" />
    </rule>
</ruleset>

pre-commit

#!/bin/sh

# Run PHP code sniffer over the files that are about to be committed.
# Add to $GITROOT/.git/hooks/pre-commit

# Make sure the command can be run regardless of where you are in the
# project tree.
gitroot=$(git rev-parse --show-toplevel)
standards="phpcs.user.xml,phpcs.xml"
phpcs="docker run --rm -v $gitroot:/data -v $HOME/config/phpcs.xml:/data/phpcs.user.xml cytopia/phpcs -s --runtime-set ignore_warnings_on_exit true -p --colors -n --cache=cache/phpcs/precommit --extensions=php --ignore=*/vendor/* --standard=$standards"

# Work out what files are queued up for committing.
filesToCheck=$(git diff-index --name-only --cached --diff-filter=ACMR HEAD -- )

# If there are any files to check, then check them.
# If there are any deleted files and phpcs passes, they will be included in
# the commit.
if [[ -n $filesToCheck ]]
then
    $phpcs $filesToCheck
    exit
fi

Revision 8: Removed deleted file checking because it was breaking git commit --amend.

Revision 9: Removed debug because I fail.

Revision 10: Use a dockerised phpcs. Saves having to install phpcs everywhere via composer.