An alternative to testing whether the output of git status --porcelain is empty is to test each condition you care about separately. One might not always care, for example, if there are untracked files in the output of git status.
For example, to see if there are any local unstaged changes, you can look at the return code of:
git diff --exit-code
To check if there are any changes that are staged but not committed, you can use the return code of:
git diff --cached --exit-code
Finally, if you want to know about whether there are any untracked files in your working tree that aren’t ignored, you can test whether the output of the following command is empty:
git ls-files --other --exclude-standard --directory
Update: You ask below whether you can change that command to exclude the directories in the output. You can exclude empty directories by adding --no-empty-directory, but to exclude all directories in that output I think you’ll have to filter the output, such as with:
git ls-files --other --exclude-standard --directory | egrep -v '/$'
The -v to egrep means to only output lines that don’t match the pattern, and the pattern matches any line that ends with a /.