Shell script helper for git commits

You must quote the variable in your script.

#!/bin/bash -e
commit_message="$1"
git add . -A
git commit -m "$commit_message"
git push

I also set "-e" so that if there are any errors, the script will exit without processing subsequent commands.

As to your second question, the . in the script should refer to your current working directory, as you intend. However the -A is causing it to add all files that have been modiied in the repo.

You can create alias with argument. Something like:

[alias]
  cap = "!git add . && git commit -m '$1' && git push origin"

with and Alias I couldn`t put variables in the middle of the sentence, but you can create a function and put it on your .bashrc like this

commit(){
  git add --all . && git commit -m '$1' && git push origin master
}