191 lines
2.8 KiB
Markdown
191 lines
2.8 KiB
Markdown
# diff Command Reference
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The `diff` command is a standard Unix/Linux utility used to compare files line by line. It is commonly used in development, DevOps, and system administration to identify changes between configuration files, source code, logs, or generated outputs.
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---
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## 1. Basic File Comparison
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Compare two files line by line:
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```bash
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diff file1 file2
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```
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### Output Behavior
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* Shows only the lines that differ
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* Uses symbols to indicate changes:
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* `<` line from `file1`
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* `>` line from `file2`
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* `c` change
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* `a` addition
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* `d` deletion
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---
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## 2. Side-by-Side Comparison
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Display files next to each other:
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```bash
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diff -y file1 file2
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```
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### Notes
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* Useful for human-readable comparison
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* Differences are shown in two columns
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* Change indicators appear in the middle
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Limit output width:
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```bash
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diff -y --width=120 file1 file2
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```
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Suppress common lines:
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```bash
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diff -y --suppress-common-lines file1 file2
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```
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---
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## 3. Unified Diff Format (Most Common)
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Generate a unified diff:
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```bash
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diff -u file1 file2
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```
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### Why Unified Diff
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* Standard format used by Git, patch, and code reviews
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* Shows context before and after changes
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* Easier to read and apply
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Example output markers:
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* `+` added lines
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* `-` removed lines
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* `@@` line numbers and context
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---
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## 4. Save Diff Output to a File
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Redirect diff output to a file:
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```bash
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diff -u file1 file2 > different.diff
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```
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Common use cases:
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* Code reviews
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* Patch creation
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* Change tracking
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* CI/CD artifact storage
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---
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## 5. Recursive Directory Comparison
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Compare directories:
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```bash
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diff -r dir1 dir2
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```
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Unified recursive diff:
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```bash
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diff -ru dir1 dir2
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```
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Ignore missing files:
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```bash
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diff -rq dir1 dir2
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```
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---
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## 6. Ignore Differences
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Ignore whitespace:
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```bash
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diff -w file1 file2
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```
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Ignore blank lines:
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```bash
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diff -B file1 file2
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```
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Ignore case differences:
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```bash
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diff -i file1 file2
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```
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---
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## 7. Apply a Diff as a Patch
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Create a patch:
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```bash
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diff -u oldfile newfile > change.patch
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```
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Apply patch:
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```bash
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patch < change.patch
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```
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Dry-run patch:
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```bash
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patch --dry-run < change.patch
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```
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---
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## 8. diff vs Git diff
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| diff | git diff |
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| -------------------- | ------------------------------- |
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| Compares any files | Compares Git-tracked files |
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| Works without Git | Requires Git repository |
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| Produces patch files | Integrated with version control |
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---
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## 9. Best Practices
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* Use `-u` format for readability and compatibility
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* Store diff files with `.diff` or `.patch` extensions
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* Avoid committing generated diff files unless required
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* Use `diff` for system configuration audits
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* Use `git diff` inside Git repositories
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---
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## 10. Quick Reference
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```bash
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diff file1 file2
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diff -y file1 file2
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diff -u file1 file2
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diff -ru dir1 dir2
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diff -u file1 file2 > change.diff
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```
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