I need some guidance with my Git hook for pre-commit using Bash

Please use:

if ( mvn compile ) ; then

[ is for runing test command in really

A nice way to create menus in bash is with the select command, here's an example (assumed to be run somewhere in the project directory):

#! /bin/bash

cmds=("Commit" "Compile and commit")
select cmd in "${cmds[@]}"; do
    pushd "$(git rev-parse --show-toplevel)"
    echo "You picked $cmd, working dir changed to $(pwd)"
    if [[ $cmd == "Compile and commit" ]]; then
        mvn compile
        if [[ $? != "0" ]]; then
            echo "Something went wrong"
        else
            echo "Compilation ok!"
        fi
    fi
    #git commit
    popd
    echo "Done, working dir now $(pwd)"
    break
done

Without addressing either maven, or whether this is a reasonable thing to be doing in a pre-commit hook, there are several points to consider here:

• Git hooks are run in some directory.

  The precise current-working-directory for the hook varies. If git commit is run anywhere within the repository tree, the pre-commit hook itself runs in the top level of the Git repository. This is true regardless of which sub-directory you are in:

  $ cat .git/hooks/pre-commit
  #! /bin/sh
  echo precommit: pwd = $(pwd)
  exit 1
  $ git commit
  precommit: pwd = [snip]/git
  $ cd Documentation
  $ git commit
  precommit: pwd = [snip]/git
  

  Note that this was not .../git/Documentation despite the fact that I was in the Documentation sub-directory.

  If git commit is run elsewhere, the current working directory may not be the top level of the repository, and may in fact be entirely unrelated to the repository itself, or the work-tree:

  $ cd /tmp
  $ git --git-dir=$HOME/src/kernel.org/git/.git commit
  precommit: pwd = /tmp
  

  It is therefore vital to: (1) constrain the location where git commit is run, or (2) avoid using the current working directory at all. I put this in bold because of the third point below. However, if you like, you can treat the current working directory as the work-tree: there is no need to attempt to cd ../.. out of the .git/hooks directory.

• The standard input of a Git hook is often not connected to the user's terminal—assuming there is a user and a terminal in the first place. For example:

  $ cat .git/hooks/pre-commit
  #! /bin/sh
  if [ -t 0 ]; then
      echo precommit: stdin is a tty
  else
      echo precommit: stdin is NOT a tty
  fi
  exit 1
  $ git commit
  precommit: stdin is NOT a tty
  

  While you can attempt to open /dev/tty, this will only work if there is a /dev/tty to open, so there is a risk here.

• During a git commit, the contents of the work tree are not the contents that will be committed. What will be committed is whatever is in the index. Examining the work-tree is only correct if the index matches the work-tree. You can test for this using the require_clean_work_tree shell function in git-sh-setup, which is in the git --exec-path, and git --exec-path has been added at the front of $PATH, so you can simply run:

  . git-sh-setup
  require-clean-work-tree "commit" "message to emit if work tree is not clean"
  

  for instance (the two arguments are the action and the message to produce on failure).

That said, the other issue you found is that:

[ expression ]

is the syntax to run the [ command, passing it expression ] as its parameters. (The [ command is also known as the test command; when invoked as test <expression> it does not demand a final ] argument, and otherwise works the same as when run as [.) You wanted to run the mvn command, not the [ or test command.