Shell script to check git for changes and then loop through changed files?

Question

I am trying write a shell script that does the following:

1. Checks the remote git repository for any changes to pull.
2. If there are changes in the remote git repository pull those changes.
3. Loops through the files that are new or have been modified.

Through my research I have found some of the necessary commands to do these things but I haven't been able to get them to work together in a shell script.

Here is a script with some of the commands that I have:

#!/bin/sh

#Check if there are any changed files
git --git-dir="/dir/.git" fetch origin

if git --git-dir="/dir/.git" log HEAD..origin/master --oneline
then

#Output the modified files from the last pull
        git --git-dir="/dir/.git" diff --name-status ORIG_HEAD..

fi

The things that I have not been able to get working with the commands in this script are:

1. The if statement to check if there are changes or not always is true. I have tried if statements with other git commands and they also are always true. It seems that git does not work like normal shell commands where you get a 0 or 1 response. How can I get a git command like this or other git commands to return the right responses in an if statement?
2. How can I assign the variables output from the command to see the changed files to an array so that I can loop through them using a for?

If the commands in my script won't really work in this case what is a better way to do this?

Edit: Sorry should have been more clear when I loop through the changed files I need to pull the changes from the remote repository before I loop through the files so that when I work with these files I have the latest changes.

Answer 1

For your first question, you can use git diff --quiet (or git diff --exit-code, but generally when you're using it for its exit code you want it not to print output anyhow, and git diff --quiet implies --exit-code) to determine if there have been any changes. That will give you a 1 value if there are changes, and a 0 if there are not. So if you want to have code that will run only if there are changes:

if ! git --git-dir="/dir/.git" diff --quiet
then
    # do stuff...
fi

For your second question, I'd recommend a while read ... loop to read lines from git diff-tree:

git --git-dir="/dir/.git" diff-tree ORIG_HEAD.. | \
    while read srcmode dstmode srcsha dstsha status srcfile dstfile
    do
        # do something with $srcfile and $dstfile
    done

Note that $srcmode will have an extra : at the beginning, and $dstfile will only have a value if the file was renamed. If you don't want to worry about renames, pass in --no-renames, and instead of seeing renames you'll see just the adds and deletes.

Answer 2

You can simply use git diff --name-only to list all filenames of files changed.

For example, here a simple script to list all PHP files edited and test the syntax.

#!/bin/bash
files=`git diff --name-only | grep -E '.php$' `
for file in $files; do
  php -l $file
done

Answer 3

You're right, git does not normally exit with nonzero status unless there's an error. The easiest way I've found to detect uncommitted changes is something like this:

 let changes=0
 while read status filename; do
    let changes=1
    # do something with this filename/status
 done < <(git status --porcelain)
 if (( ! changes )); then
    echo "No changes."
 fi

In general, if you're going to try to drive git from code, you should use --porcelain on those subcommands which support it, to make it act in a more automation-friendly fashion. You may also want to investigate libraries for other languages to interact with git without constructing your own shell commands; for instance, in Ruby there's grit.

Now, in your case, you want to detect what changed upstream. For that, you probably want to use git diff-tree. Similar logic to the above:

 git fetch   # not pull
 while read filename; do
   # do something with filename
 done < <(git diff-tree --name-only origin/master master)  # or whatever branch you're using

Answer 4

If you're scripting and want to make sure the repo is in a committed state (e.g. no new, modified, or staged files), try this:

# Get to code.  Exit if unsaved changes in repo
if `git status | grep -q "nothing to commit"`; then
  git checkout --quiet $BRANCH || exit 1
else
  echo "ERROR: repo has unsaved changes"
  exit 1
fi

This is the simplest thing I could find that checked for new, changed, and staged files.