gitignore binary files that have no extension

How can binary files be ignored in git using the .gitignore file?

Example:

$ g++ hello.c -o hello

The "hello" file is a binary file. Can git ignore this file ?

# Ignore all
*

# Unignore all with extensions
!*.*

# Unignore all dirs
!*/

### Above combination will ignore all files without extension ###

# Ignore files with extension `.class` & `.sm`
*.class
*.sm

# Ignore `bin` dir
bin/
# or
*/bin/*

# Unignore all `.jar` in `bin` dir
!*/bin/*.jar

# Ignore all `library.jar` in `bin` dir
*/bin/library.jar

# Ignore a file with extension
relative/path/to/dir/filename.extension

# Ignore a file without extension
relative/path/to/dir/anotherfile

Add something like

*.o

in the .gitignore file and place it at the root of your repo ( or you can place in any sub directory you want - it will apply from that level on ) and check it in.

Edit:

For binaries with no extension, you are better off placing them in bin/ or some other folder. Afterall there is no ignore based on content-type.

You can try

*
!*.*

but that is not foolproof.

To append all executables to your .gitignore (which you probably mean by "binary file" judging from your question), you can use

find . -executable -type f >>.gitignore

If you don't care about ordering of lines in your .gitignore, you could also update your .gitignore with the following command which also removes duplicates and keeps alphabetic ordering intact.

T=$(mktemp); (cat .gitignore; find . -executable -type f | sed -e 's%^\./%%') | sort | uniq >$T; mv $T .gitignore

Note, that you cannot pipe output directly to .gitignore, because that would truncate the file before cat opens it for reading. Also, you might want to add \! -regex '.*/.*/.*' as an option to find if you do not want to include executable files in subdirectories.