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README

golang-diff

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.

Features

• 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.

Visual Comparison

Standard Diff (Unified)

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

golang-diff (Side-by-Side)

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.

Installation

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.

Usage (CLI)

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

Compare Two Files

Compare two individual files side-by-side:

diff compare <file1> <file2> [flags]

Recursive Directory Diff

Compare two directories recursively:

diff diff <dir1> <dir2> [flags]

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

Apply Patch

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

diff patch <patchFile> <targetDir>

Flags

• --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).

Examples

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/

Output Guide

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

Symbols

Symbol	Meaning	Color (Term Mode)
==	Lines are identical	Green
1d	One continuous difference block	Red
2d	Two difference blocks	Red
d	Multiple difference blocks	Red
w	Whitespace difference only	Yellow
q	Mixed character and whitespace difference	Red
$	End of Line (EOL) difference (e.g., CRLF vs LF)	Yellow

Colors

When terminal mode is enabled (-t):

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

Example Output

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.

Usage (Library)

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

Import

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

Example

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)
}

Development

To run the tests:

go test ./...

Documentation

Index

• func CompareFiles(file1 string, file2 string, term bool, interactive bool, maxLines int)
• func DiffFiles(path1, path2 string, term bool, interactive bool, maxLines int, ...)
• func PatchFiles(patchFile string, targetDir string)

Functions

func CompareFiles

func CompareFiles(file1 string, file2 string, term bool, interactive bool, maxLines int)

CompareFiles is a subcommand `diff compare` Compares two files side by side.

Flags:

file1: @1 File 1 path
file2: @2 File 2 path
term: --term -t Terminal mode (colors)
interactive: --interactive -i Interactive mode
maxLines: --max-lines -m (default: 1000) Max lines to search for alignment

func DiffFiles

func DiffFiles(path1, path2 string, term bool, interactive bool, maxLines int, selectFile string)

DiffFiles is a subcommand 'diff diff' Compares two paths (files or directories) recursively.

Flags:

path1: @1 Path 1
path2: @2 Path 2
term: --term -t Terminal mode (colors)
interactive: --interactive -i Interactive mode
maxLines: --max-lines -m (default: 1000) Max lines to search for alignment
selectFile: --select-file -s Glob pattern to filter files

func PatchFiles

func PatchFiles(patchFile string, targetDir string)

PatchFiles is a subcommand 'diff patch' Applies a patch file to a target directory.

Flags:

patchFile: @1 Patch file path
targetDir: @2 Target directory path