Make Git automatically remove trailing white space before committing

Those settings (core.whitespace and apply.whitespace) are not there to remove trailing whitespace but to:

• core.whitespace: detect them, and raise errors
• apply.whitespace: and strip them, but only during patch, not "always automatically"

I believe the git hook pre-commit would do a better job for that (includes removing trailing whitespace)

Note that at any given time you can choose to not run the pre-commit hook:

• temporarily: git commit --no-verify .
• permanently: cd .git/hooks/ ; chmod -x pre-commit

Warning: by default, a pre-commit script (like this one), has not a "remove trailing" feature", but a "warning" feature like:

if (/\s$/) {
    bad_line("trailing whitespace", $_);
}

You could however build a better pre-commit hook, especially when you consider that:

Committing in Git with only some changes added to the staging area still results in an “atomic” revision that may never have existed as a working copy and may not work.

For instance, oldman proposes in another answer a pre-commit hook which detects and remove whitespace.
Since that hook get the file name of each file, I would recommend to be careful for certain type of files: you don't want to remove trailing whitespace in .md (markdown) files!

Another approach, suggested by hakre in the comments:

You can have two spaces at end of line in markdown and not have it as trailing whitespace by adding "\" before \n.

Then a content filter driver:

git config --global filter.space-removal-at-eol.clean 'sed -e "s/ \+$//"'
# register in .gitattributes 
*.md filter=space-removal-at-eol

On macOS (or, likely, any BSD), the sed command parameters have to be slightly different. Try this:

#!/bin/sh

if git-rev-parse --verify HEAD >/dev/null 2>&1 ; then
   against=HEAD
else
   # Initial commit: diff against an empty tree object
   against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

# Find files with trailing whitespace
for FILE in `exec git diff-index --check --cached $against -- | sed '/^[+-]/d' | sed -E 's/:[0-9]+:.*//' | uniq` ; do
    # Fix them!
    sed -i '' -E 's/[[:space:]]*$//' "$FILE"
    git add "$FILE"
done

Save this file as .git/hooks/pre-commit -- or look for the one that's already there, and paste the bottom chunk somewhere inside it. And remember to chmod a+x it too.

Or for global use (via Applying a git post-commit hook to all current and future repos) you can put it in $GIT_PREFIX/git-core/templates/hooks (where GIT_PREFIX is /usr or /usr/local or /usr/share or /opt/local/share) and run git init inside your existing repos.

According to git help init:

Running git init in an existing repository is safe. It will not overwrite things that are already there. The primary reason for rerunning git init is to pick up newly added templates.

I'd rather leave this task to your favorite editor.

Just set a command to remove trailing spaces when saving.

This doesn't remove white space automatically before a commit, but it is pretty easy to effect. I put the following Perl script in a file named git-wsf (Git white space fix) in a directory in $PATH, so I can:

git wsf | sh

And it removes all white space only from lines of files that Git reports as a diff.

#! /bin/sh
git diff --check | perl -x $0
exit

#! /usr/bin/perl

use strict;

my %stuff;
while (<>) {
    if (/trailing whitespace./) {
        my ($file,$line) = split(/:/);
        push @{$stuff{$file}},$line;
    }
}

while (my ($file, $line) = each %stuff) {
    printf "ex %s <<EOT\n", $file;
    for (@$line) {
        printf '%ds/ *$//'."\n", $_;
    }
    print "wq\nEOT\n";
}

Python Script for the same result.

import subprocess                                                                 
                                                                              
def get_trailing_lines():                                                         
                                                                              
    result = subprocess.run([                                                     
                            'git',                                            
                            'diff',                                           
                            '--check'                                         
                        ], capture_output=True)                               
                                                                              
    return result.stdout.decode().split('\n')                                     
                                                                              
                                                                              
def modify_line(file_path, l_num):                                                
                                                                              
    f_lines = open(file_path).readlines()                                         
    f_lines[l_num] = f_lines[l_num].rstrip()+'\n'\                                
                     if '\n' in f_lines[l_num] else f_lines[l_num].rstrip()    
                                                                              
    with open(file_path, "w") as w_fp:                                            
        w_fp.writelines(f_lines)                                                  
                                                                              
                                                                              
if __name__ == '__main__':                                                        
                                                                              
    l = get_trailing_lines()                                                      
    for m, d in zip(l[::2], l[1::2]):                                             
        f_path, l_no, *_ = m.split(":")                                           
        modify_line(f_path, int(l_no)-1)                                          

This probably won't directly solve your problem, but you might want to set those via git-config in your actual project space, which edits file ./.git/config as opposed to file ~/.gitconfig. It is nice to keep the settings consistent among all project members.

git config core.whitespace "trailing-space,space-before-tab"
git config apply.whitespace "trailing-space,space-before-tab"