runblock

README

runblock

runblock is a tool for executing code blocks in Markdown files using external commands.

Usage

Basic usage

$ runblock example.md

Read from stdin

$ cat example.md | runblock

With default command

$ runblock --default-command "cat" example.md

With language-specific commands

Use -c to specify commands for specific languages:

$ runblock -c 'go:gofmt' -c 'python:python3' example.md

Multiple -c flags can be used to specify different commands for different languages.

Watch mode

You can use the --watch flag to continuously monitor changes to your Markdown file and automatically re-run when the file is modified:

$ runblock --watch example.md

This is useful during development as it allows you to see changes in real-time as you edit the Markdown file.

How it works

runblock parses Markdown files and extracts fenced code blocks. Each code block can specify a command in the info string after the language identifier.

Specifying commands in code blocks

Commands are specified after the language identifier, separated by a space:

```go /usr/bin/gofmt
package main

func main() {}
```

When runblock processes this block, it executes /usr/bin/gofmt with the code block content.

Template variables

Commands support template variables using CEL (Common Expression Language) syntax:

Variable	Description
{{lang}}	Language identifier of the code block
{{content}}	Content of the code block
{{i}}	Index of the code block (0-based)

CEL expressions are supported within {{ }}:

# Ternary operator
{{ lang == "" ? "txt" : lang }}

# String concatenation
{{ "prefix_" + lang }}

# Arithmetic
{{ i + 1 }}

Environment variables

The following environment variables are set when executing commands:

Variable	Description
CODEBLOCK_LANG	Language identifier of the code block
CODEBLOCK_CONTENT	Content of the code block
CODEBLOCK_INDEX	Index of the code block (0-based)

Standard input

The code block content is also passed to the command via stdin.

Examples

Convert code blocks to images

```go /path/to/code2img {{lang}} -o output_{{i}}.png
package main

func main() {
    fmt.Println("Hello, World!")
}
```

Format code blocks

```go gofmt
package main
func main(){fmt.Println("hello")}
```

Execute code blocks

```python python3
print("Hello from Python")
```

Using default command for all blocks

$ runblock --default-command "cat > block_{{i}}.txt" example.md

This saves each code block to a separate file.

Installation

Homebrew:

$ brew install k1LoW/tap/runblock

go install:

$ go install github.com/k1LoW/runblock@latest

Flags

Flags:
  -c, --command stringArray      command for specific language (format: lang:command, e.g., 'go:gofmt')
      --default-command string   default command for code blocks without explicit command
  -h, --help                     help for runblock
  -v, --version                  version for runblock
  -w, --watch                    watch the file for changes and re-run on modifications

Command priority

Commands are resolved in the following order (highest priority first):

1. Command specified in the code block info string (e.g., ```go gofmt)
2. Language-specific command via -c flag
3. Default command via --default-command flag

Documentation

Overview

Copyright © 2026 Ken'ichiro Oyama <k1lowxb@gmail.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.