Comparing Text and Code: Tools and Methods

Comparing text and code is a fundamental development task: code review, branch merging, configuration audits, and contract checks. This article covers algorithms, tools, and practical comparison methods.

To quickly compare two texts or code snippets, use Diff Checker on rechecker.ru.

Why compare text

Comparison algorithms

Longest Common Subsequence (LCS)

This classic algorithm finds the longest common subsequence. Its complexity is O(n*m), where n and m are the lengths of the strings.

Файл A: ABCDEF
Файл B: ACDEFG
LCS:    ACDEF

Myers diff

An optimized algorithm used by Git. It minimizes the number of changes in the output. Its complexity is O(ND), where N is the sum of the lengths and D is the size of the diff.

Patience diff

A variant for code: it first matches unique lines, then fills in the rest. It produces more readable diffs for refactoring.

Output formats

Unified diff (standard)

--- file1.txt
+++ file2.txt
@@ -1,4 +1,4 @@
-старая строка
+новая строка
  без изменений
  без изменений

Change symbols

Context diff

*** file1.txt
--- file2.txt
***************
*** 1,4 ****
- старый текст
  общий контекст
--- 1,4 ----
+ новый текст
  общий контекст

Command-line tools

diff

diff file1.txt file2.txt
diff -u file1.txt file2.txt    # unified
diff -r dir1/ dir2/            # рекурсивно
diff -w file1 file2           # игнорировать пробелы

git diff

git diff HEAD~1              # последний коммит
git diff branch1 branch2     # между ветками
git diff --word-diff         # по словам
git diff --stat              # статистика

colordiff

colordiff file1 file2        # цветной вывод

Online tools

Online diff services are useful for:

• Comparing without installing Git
• Working with configurations and logs
• Quick checks during code review
• Comparing output from different sources

Diff Checker rechecker.ru supports text and code comparison with syntax highlighting and character-by-character mode.

Comparing by word and character

By line (default)

Each line is a unit of comparison. Suitable for code and structured text.

By word

Было:    "старый текст"
Стало:   "новый текст"
Diff:    "старый" -> "новый" (остальное без изменений)

By character

Used for short strings, passwords, and hashes. Shows exact differences.

Practical scenarios

Comparing Nginx configurations

diff -u /etc/nginx/sites-available/default /etc/nginx/sites-available/backup

Comparing JSON

diff <(jq -S . file1.json) <(jq -S . file2.json)

Sorting keys (jq -S) removes the effect of field order.

Ignoring whitespace

diff -w file1 file2          # все пробелы
diff -B file1 file2          # пустые строки
diff -b file1 file2          # пробелы в конце строк

CI/CD integration

File comparison is part of build pipelines:

# Пример: проверка изменений конфигурации
- name: Compare configs
  run: |
    diff -u config.prod.yaml config.staging.yaml || true

# Git diff в отчёте
- name: Generate diff report
  run: git diff HEAD~1 --stat > diff-report.txt

Comparing three or more versions

Three-way comparison (3-way merge) is used to merge changes from multiple branches. Tools: diff3, meld, kdiff3, built into Git.

diff3 ours.txt base.txt theirs.txt

Comparing in an IDE

Recommendations

1. Use unified format — it is more readable and standard for patches
2. Ignore nonessential differences — whitespace, case, where appropriate
3. Limit the context — for large files, show only the changed sections
4. Preserve the encoding — UTF-8 for correct display of Cyrillic text
5. Normalize before comparison — sort JSON keys, remove trailing whitespace

For regular comparison of configurations, logs, and code snippets, Diff Checker on rechecker.ru provides a quick result without installing additional software.