Text Diff Checker — Developer Code Samples

Text diff algorithms compare two strings or files and highlight additions, deletions, and changes. Python's difflib generates unified and HTML diffs. The Unix diff command and Node's diff package provide similar functionality for CI pipelines and code review tools.

Try the interactive version online: Open Text Diff Checker Tool →

Parameters

Parameter	Type	Required	Description
text1	str	Yes	Original text (left side / before)
text2	str	Yes	Modified text (right side / after)
diff_type	str	No	Diff format: unified, context, html, sidebyside (default: unified)

Returns: Diff output as string with additions (+), deletions (-), and context lines

Code Examples

import difflib

# Unified diff (like git diff output)
text1 = """Line 1: Hello World
Line 2: This is unchanged
Line 3: This will be modified
Line 4: Goodbye World"""

text2 = """Line 1: Hello World
Line 2: This is unchanged
Line 3: This has been modified
Line 4: See you later"""

lines1 = text1.splitlines(keepends=True)
lines2 = text2.splitlines(keepends=True)

# Generate unified diff
diff = list(difflib.unified_diff(lines1, lines2, fromfile='original.txt', tofile='modified.txt'))
print(''.join(diff))

# Context diff (shows more surrounding context)
context_diff = list(difflib.context_diff(lines1, lines2, fromfile='original.txt', tofile='modified.txt'))
print(''.join(context_diff))

# HTML diff (colored output for web)
html_diff = difflib.HtmlDiff(wrapcolumn=80)
html_output = html_diff.make_file(lines1, lines2, fromdesc='Original', todesc='Modified')
with open('diff.html', 'w') as f:
    f.write(html_output)

# Simple line-by-line comparison
matcher = difflib.SequenceMatcher(None, lines1, lines2)
for tag, i1, i2, j1, j2 in matcher.get_opcodes():
    if tag == 'equal':
        print(f"  {lines1[i1].rstrip()}")
    elif tag == 'replace':
        print(f"- {lines1[i1].rstrip()}")
        print(f"+ {lines2[j1].rstrip()}")
    elif tag == 'delete':
        print(f"- {lines1[i1].rstrip()}")
    elif tag == 'insert':
        print(f"+ {lines2[j1].rstrip()}")

# Similarity ratio (0.0 to 1.0)
ratio = difflib.SequenceMatcher(None, text1, text2).ratio()
print(f"Similarity: {ratio:.1%}")

// Install: npm install diff

// Using diff package (npm install diff)
const Diff = require('diff');

const text1 = `Line 1: Hello World
Line 2: This is unchanged
Line 3: This will be modified`;

const text2 = `Line 1: Hello World
Line 2: This is unchanged
Line 3: This has been modified`;

// Unified diff
const patch = Diff.createPatch('file.txt', text1, text2, 'Original', 'Modified');
console.log(patch);

// Line-by-line diff
const lineDiff = Diff.diffLines(text1, text2);
lineDiff.forEach(part => {
  const prefix = part.added ? '+ ' : part.removed ? '- ' : '  ';
  const color = part.added ? '\x1b[32m' : part.removed ? '\x1b[31m' : '\x1b[0m';
  process.stdout.write(color + prefix + part.value + '\x1b[0m');
});

// Word-level diff
const wordDiff = Diff.diffWords(text1, text2);
wordDiff.forEach(part => {
  if (part.added) process.stdout.write('[+' + part.value + ']');
  else if (part.removed) process.stdout.write('[-' + part.value + ']');
  else process.stdout.write(part.value);
});

// Character-level diff
const charDiff = Diff.diffChars('Hello World', 'Hello W0rld');
charDiff.forEach(part => {
  if (part.added) process.stdout.write('[+' + part.value + ']');
  else if (part.removed) process.stdout.write('[-' + part.value + ']');
  else process.stdout.write(part.value);
});

# Basic diff (line-by-line)
diff file1.txt file2.txt

# Unified diff format (like git diff)
diff -u file1.txt file2.txt

# Side-by-side diff
diff -y file1.txt file2.txt

# Ignore whitespace differences
diff -w file1.txt file2.txt

# Ignore blank lines
diff -B file1.txt file2.txt

# Color output (GNU diff)
diff --color=always -u file1.txt file2.txt

# Diff two strings inline
diff <(echo "Hello World") <(echo "Hello W0rld")

# Count differences
diff file1.txt file2.txt | grep -c '^[<>]'

# Git-style diff with Python
python3 -c "
import difflib, sys
a = open(sys.argv[1]).readlines()
b = open(sys.argv[2]).readlines()
print(''.join(difflib.unified_diff(a, b, sys.argv[1], sys.argv[2])))
" file1.txt file2.txt

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