Ways to see what a command would do, without actually carrying out the action.

.gitignore

To list the files that don't match .gitignore:

• git ls-files -ocm --exclude-standard
• git status -u

To list the files that do match .gitignore:

• (git ls-files -oi --exclude-standard; git ls-files -oi --exclude-standard --directory) | sort | uniq
• (git ls-files -oi --exclude-standard; git ls-files -oi --exclude-standard --directory) | perl -nle '$seen{$_}++||next;if(-d){system"find",$_,"-type","f"}else{print}'
• git clean -ndX

To list both together:

(git ls-files -ocm --exclude-standard | perl -ple 's/^/+ /'; (git ls-files -oi --exclude-standard; git ls-files -oi --exclude-standard --directory) | perl -nle '$seen{$_}++||next;if(-d){system"find",$_,"-type","f"}else{print}' | perl -ple 's/^/- /') | sort

built-in

• git add -n
• git commit --dry-run