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CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

What is pk?

pk is a Rust command-line field extraction utility — a middle ground between cut and awk for selecting columns from input streams. It handles variable whitespace, quoted/escaped delimiters, empty fields, field ranges, and exclude patterns.

Build Commands

Requires Rust toolchain (cargo).

# Build (debug)
cargo build

# Build (release, optimized + stripped)
cargo build --release

# Run tests
cargo build && test/system/run

# Run a single test manually
cd test/system && PK=../../target/debug/pk . <name>.cmd < <name>.in

Testing

Tests are system/integration tests in test/system/. Each test case is a triplet:

  • <name>.cmd — shell command invoking $PK with flags
  • <name>.in — input fed via stdin
  • <name>.out — expected output

The test/system/run script iterates all .cmd files, compares output via md5/md5sum. Set PK env var to override the binary path (default: ../../target/debug/pk).

Architecture

Single-file implementation in src/main.rs. The pipeline is: CLI parsing → tokenizer → field printer.

  • CLI / Config — Uses clap for arg parsing. Optional-value flags (-E, -N, -q) are handled by argv preprocessing before clap, since argp-style "attached value only" semantics aren't natively supported by clap.
  • Tokenizer (tokenize()) — Splits input lines into a Vec<String> of tokens. Handles delimiters, quoting, backslash escaping, empty fields, trimming, and exclude string removal.
  • Field Printer (print_fields()) — Takes parsed field specs (indices, ranges, literal strings) and a token list, prints selected fields to stdout via buffered writer.
  • Field Spec — Enum with Number(usize), Range(usize, Option<usize>), and Literal(String) variants.