I think, most of you know about Git repository's support for hooks. One of those hooks is pre-commit, which will be called before whenever a commit is been made. So I have created one Git pre-commit hook script specifically for PHP & Drupal 7 (Can be customized for your purpose as well) git repository. You can fork or download it from manojapare/pre-commit
For using this hook script just copy/download the script file to your git repository hooks folder that is in.git/hooks/. Don't forget to give executable permission for the script file.
Whenever a git commit is been performed, pre-commit hook script will be executed by git inbuilt hook support. The above script does syntax check as well as looks for any debugging function in the changes staged to commit (which is a bad practice). In both case, the commit operation will be aborted and can be committed after doing corrections or removing the debugging function from the code.
In case you want to force commit with any debugging functions (not recommended) you can do it by using the git command option -n OR --no-verify.
Syntax check is been performed using php -l command for each php files (file with extensions 'php, inc and module').
Check for debugging functions
Checking for debugging function is been performed using git diff command only to files staged to commit and in turn only to added/modified changes.
For better performance of the script, I have excluded the checking of files with following extensions: 'info, png, gif, jpg, ico, patch, htaccess, sh, ttf, woff, eot, svg'. Also excluded files residing in the following directories: 'features, contrib, devel, libraries'.
Merge conflict marker check
Merge conflict marker check is been performed to all files staged to commit using egrep pattern "(<<<<|====|>>>>)+.*(\n)?".