# Esl Selectn

> Use when reservoir-sampling a fixed number of random lines from a large text file or stream without loading the whole file.

- Skill: `vimalinx/esl-selectn` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds add vimalinx/esl-selectn`
- Raw SKILL.md: https://api.skillmd.com/api/skills/vimalinx/esl-selectn/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: vimalinx (https://skillmd.com/u/vimalinx)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/vimalinx/esl-selectn

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# esl-selectn

## Quick Start

- **Command:** `esl-selectn [-options] <n> <file>`
- **Local executable:** `/home/vimalinx/miniforge3/envs/bio/bin/esl-selectn`
- **Extended help:** See `references/help.md`

## When To Use This Tool

- Use `esl-selectn` when the thing you want to sample is one physical line per record.
- It is useful for downsampling huge ID lists, score tables, one-record-per-line exports, or stdin streams in a single pass.
- Reach for `--seed` when you need the same sampled subset on repeated runs.

## Common Patterns

```bash
# Sample 100 random lines from a text file
esl-selectn 100 all-records.txt > sample.txt

# Reproducible sampling with a fixed seed
esl-selectn --seed 42 500 ids.txt > ids.sample.txt

# Sample directly from a stream
cat metrics.tsv | esl-selectn 1000 - > metrics.sample.tsv
```

## Recommended Workflow

1. Make sure each logical record you care about is represented by exactly one line.
2. Choose the sample size `n` and whether you need reproducibility.
3. Run `esl-selectn` on the file or stream, redirecting stdout to the sampled output.
4. Validate the sampled line count and spot-check that the input format survived intact.

## Guardrails

- This tool samples lines, not FASTA, FASTQ, or Stockholm records. Multi-line biological records must be flattened or sampled by another method first.
- The implementation is single-pass reservoir sampling, so memory scales with `n`, not with full file size.
- `-h` works; `--help` and `--version` are rejected by the local executable.
- `file` may be `-` to read from stdin.