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Takahiro Sato
Takahiro Sato

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In-Place Markdown Editing with mq's --update Flag

#markdown #cli #rust #automation

When managing documentation across multiple markdown files, manual editing becomes inefficient. The mq command-line tool includes an --update flag that modifies files in place while preserving their markdown structure.

demo

In-Place File Modification

Most markdown processors output filtered results without modifying source files. The -U or --update flag changes this behavior by updating the original markdown structure, replacing specific nodes with query results.

# Basic syntax for updates mq --update 'your_query_here' file.md
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Update Examples

1. Batch URL Updates

Replace URLs across multiple files:

# Update specific URLs across all markdown files mq -U 'if (and(or(.link, .definition), matches_url("old-domain.com"))): update(replace("old-domain.com", "new-domain.com"))' docs/**/*.md
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Before:

See our [API docs](https://old-domain.com/api) [Reference]: https://old-domain.com/reference
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After:

Check out our [API docs](https://new-domain.com/api) [Reference]: https://new-domain.com/reference
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2. Content Standardization

Standardize code block languages across your documentation:

# Convert all 'js' code blocks to 'javascript' mq -U '.code | if (attr("lang") == "js"): set_attr("lang", "javascript")' *.md
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3. Header Consistency

Ensure consistent header formatting:

# Remove trailing colons from headers mq -U '.h | if (ends_with(":")): update(rtrimstr(":"))' documentation.md
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Before:

# Getting Started: ## Installation:
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After:

# Getting Started ## Installation
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4. Link Reference Cleanup

Update broken internal links:

# Fix internal link references mq -U '.link | if (starts_with("#old-section")): update(replace("#old-section", "#new-section"))' README.md
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Advanced Update Patterns

Conditional Updates

Update content based on complex conditions:

# Update deprecated badges mq -U 'if (and(.image, contains("deprecated"))): update(replace("deprecated", "legacy"))' CHANGELOG.md
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Selective Text Replacement

Replace text only in specific contexts:

# Update version numbers only in code blocks mq -U '.code | if (contains("v1.0")): update(replace("v1.0", "v2.0"))' docs/*.md
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Nested Element Updates

Modify content within complex structures:

# Update URLs inside link text mq -U '.link | if (matches_url("example.com")): update("newexample.com")' documentation/*.md
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Update Safety

Advanced Patterns

Update + Custom Functions

Create reusable update patterns:

# Save to custom.mq def modernize_badges(badge_text): if (contains("build-passing")): replace("build-passing", "build%20passing") else: badge_text; # Use it mq -U 'include "custom" | .image | modernize_badges()' README.md
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Update + File Context

Use file information in updates:

# Add file-specific prefixes mq -U 'let filename = __FILE__ | .h1 | let text = to_text() | update(s"[${filename}] ${text}")' docs/*.md
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Update Scenarios

Documentation Maintenance 

# Remove outdated warning boxes mq -U 'select(.blockquote) | if (contains("deprecated")): update("")' docs/*.md # Update installation commands mq -U '.code("bash") | if (contains("npm install old-package")): update("npm install new-package")' tutorials/*.md
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Link Management 

# Convert relative to absolute URLs mq -U '.link | if (starts_with("./")): update(replace("./", "https://docs.example.com/"))' *.md # Update image CDN URLs mq -U '.image | if (matches_url("old-cdn.com")): update(replace("old-cdn.com", "new-cdn.com"))' assets/*.md
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Implementation Details

Structure Preservation

mq parses markdown into an abstract syntax tree, unlike text replacement tools:

# This won't accidentally modify code blocks or URLs mq -U '.text | if (contains("API")): update("Interface")' docs.md
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Element Targeting

Queries target specific markdown elements:

# Only update headers, not body text mq -U '.h | if (contains("v1")): update(replace("v1", "v2"))' changelog.md
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Format Preservation

Updates maintain markdown formatting conventions:

# Preserves link formatting styles mq -U --link-title-style=double '.link | update_text("New Title")' docs.md
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Integration with Workflows

CI/CD Automation 

# GitHub Actions - uses: harehare/setup-mq@v1 - name: Update Documentation URLs run: | mq -U '.link | if (contains("staging.example.com")): update(replace("staging.example.com", "example.com"))' docs/*.md
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Installation

The easiest way to install mq is through Cargo:

cargo install --git https://github.com/harehare/mq.git mq-cli --tag v0.2.7
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For other installation methods, including Homebrew, Docker, and pre-built binaries, check the official installation guide.

Summary

The --update flag modifies mq behavior from read-only filtering to in-place file editing. The feature handles markdown transformations by operating on parsed syntax trees rather than raw text, preserving document structure during modifications.

Start with simple text replacements, then implement conditional logic for complex transformations. This approach reduces manual editing overhead in documentation maintenance workflows.

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