golang-diff is a Go library and CLI tool for comparing text files line by line and character by character. It provides colored terminal output and an interactive viewer.

• Line Alignment: Uses a hash-based lookahead algorithm to align lines efficiently.
• Character-Level Diff: Computes precise character-level differences within modified lines.
• Terminal Colors: Highlighting for additions (green) and deletions (red).
• Interactive Mode: View differences in less (or your preferred pager) for easy navigation.
• Configurable Lookahead: Adjust the search depth for line alignment.

--- file1.txt
+++ file2.txt
@@ -1,2 +1,2 @@
 Hello world
-This is a test
+This is a test case

Hello world    ==  Hello world
This is a test 1d  This is a test case

Why it's better:

• Side-by-Side View: Compare changes in context without mental context switching.
• Character-Level Precision: Highlights exactly what changed within the line (e.g., " case" added).
• Line Alignment: Hash-based lookahead ensures lines are aligned even after large insertions/deletions.

To install the CLI tool:

go install github.com/arran4/golang-diff/cmd/diff@latest

This will install the diff binary to your $GOPATH/bin directory.

The tool supports three main commands: compare, diff, and patch.

Compare two individual files side-by-side:

diff compare <file1> <file2> [flags]

Compare two directories recursively:

diff diff <dir1> <dir2> [flags]

This will walk through both directories and display diffs for all modified files.

Apply a patch generated by golang-diff to a target directory:

diff patch <patchFile> <targetDir>

• --term / -t: Enable terminal colors (default: false).
• --interactive / -i: Open the diff in an interactive pager (less) (default: false).
• --max-lines / -m: Set the maximum number of lines to search ahead for alignment (default: 1000).

Compare two files with color output:

diff compare file1.txt file2.txt -t

Compare two files interactively:

diff compare file1.txt file2.txt -i

Recursive diff:

diff diff src/ v1/src/

The output displays the two files side-by-side. The center column contains a symbol indicating the type of difference between the lines.

When terminal mode is enabled (-t):

• Green: Added or identical content.
• Red: Deleted or modified content.
• Yellow: Whitespace or EOL differences.

Hello world    ==  Hello world
This is a test 1d  This is a test case

In this example:

• The first line is identical (==).
• The second line has one difference (1d): " case" is added on the right side.

You can also use golang-diff as a library in your Go projects.

import "github.com/arran4/golang-diff/pkg/diff"

package main

import (
	"fmt"
	"github.com/arran4/golang-diff/pkg/diff"
)

func main() {
	text1 := "Hello world\nThis is a test"
	text2 := "Hello World\nThis is a test case"

	// Compare strings with options
	output := diff.Compare(text1, text2, diff.TermMode(true))

	fmt.Println(output)
}

To run the tests:

go test ./...