Merge multiple Markdown files into one stream

Goal: Concatenate several files, with the source path visible before each one, to review a set of docs in one pass.

Prerequisites: None.

Query

$ mq -S 's"\n${__FILE__}\n"' 'identity' docs/**/*.md

Input

docs/intro.md:

# Introduction
Welcome.

docs/usage.md:

# Usage
Use it like this.

Output

docs/intro.md
# Introduction
Welcome.

docs/usage.md
# Usage
Use it like this.

Notes

• -S <query> inserts the result of <query> as a separator between files; __FILE__ is a built-in variable holding the current file’s path.
• identity passes each node through unchanged, swap it for a real query to filter/transform while merging.
• This runs the query once per file and stitches the results together with -S. To instead run one query across all files at once, e.g. to count something over the whole set, use --eval-all. It has no per-file separator, so it’s for aggregation, not this kind of readable concatenation.