Comparer

Comparer is an application for comparing text files and highlighting the differences between them.

Opening from the command line

Pass two paths to open them side by side and compare them straight away:

comparer old.txt new.txt
comparer before/ after/          # two folders
comparer screenshot-a.png screenshot-b.png

Relative paths are resolved against the current directory. When started this way, the app quits when its window closes, so tools that wait for it — such as git difftool — carry on once you are done.

comparer --help lists everything it takes, and comparer --version prints the version. Both answer on the command line without opening a window:

comparer --version               # 1.2.3
comparer --help

On Windows the packaged app is a GUI binary with no console attached, so these print nothing when run bare from cmd or PowerShell. Redirect the output to see it — comparer --version | more, or comparer --version > version.txt.

Opening a patch or a diff

--diff takes a patch or diff file; --text takes the diff itself. Either compares the two texts the diff describes, rather than two files on disk. - reads standard input:

comparer --diff fix.patch
comparer --text "$(git diff)"
diff -u old.txt new.txt | comparer --text -
git diff | comparer --diff -

Quote the substitution. Unquoted, --text $(diff a b) is split on whitespace by the shell and only its first word reaches the app.

Both formats are read: the unified format that diff -u, git diff and patch files use, and the older format plain diff a b writes. Prefer unified where there is a choice — it quotes a few lines of context around each change, which is what lets the two sides line up. The older format quotes only the changed lines, so a deletion in one place and an addition in another are paired up by what they contain, and can come out as a single change rather than as two.

Only what the diff quotes can be shown. It carries the changed lines and a little context, not the whole file, so the comparison is the hunks one after another and its line numbers are the diff's own rather than the original file's. A patch describing several files opens the first and says what else it changes; a binary change is described by a patch but never quoted, so there is nothing to show for one.

Where the comparer executable lives depends on how it was installed:

Platform	Executable
Linux (deb / rpm)	comparer (on your PATH)
macOS	/Applications/comparer.app/Contents/MacOS/comparer
Windows	%LOCALAPPDATA%\comparer\comparer.exe

Using Comparer as git difftool

git config --global difftool.comparer.cmd 'comparer "$LOCAL" "$REMOTE"'
git config --global diff.tool comparer
git config --global difftool.prompt false

Then:

git difftool                 # each changed file, one window at a time
git difftool main -- src/    # against another branch, for some paths
git difftool --dir-diff      # every change at once, as a folder comparison

On macOS or Windows, use the full executable path from the table above in difftool.comparer.cmd.

Recent comparisons

Comparisons of files, images or folders opened from disk are remembered. Reopen one from Recent in the header, in the editors view.

Development

pnpm install
pnpm start        # run the app
pnpm run test     # unit tests
pnpm run lint     # prettier and eslint