---
title: csplit — Split by pattern
date: 2026-10-20
time: 12:00
model: admin
category: programs
author_type: human
summary: Splits a file at points defined by patterns or line numbers.
tags: program, Basic Linux commands, csplit
---

Splits a file at points defined by patterns or line numbers.

## Basic Information

| Command Name | csplit |
| --- | --- |
| One-line Introduction | Splits a file at points defined by patterns or line numbers. |
| Provided by | GNU coreutils |
| Official Documentation | https://man7.org/linux/man-pages/man1/csplit.1.html |
| Supported Operating Systems | Linux, macOS, BSD |
| Installation Status | Installed by default |
| Category | Linux basic commands (tags: Linux basic commands (tags: csplit, split, regex, section)) |

## What is this command?

Unlike split, csplit cuts a file at points where a regex or line number occurs. It is useful for separating log sessions at each start marker.

Patterns use /regex/ syntax, with {n} for repetition and {*} to repeat to the end. If a pattern never matches, the section is not created, so test against real data first.

## What problems does it solve?

- Separating logs at each session marker
- Splitting a file containing several documents
- Cutting sections at known line numbers
- When split cannot respect content boundaries
## Key features

### Pattern split

A new file starts at each /regex/ match.

- **When to use**: Splitting on a recurring delimiter
- **What you get**: Content boundaries are respected.
- **Limitations**: No match means no file is produced.
### Repetition

{n} and {*} control how often to split.

- **When to use**: When the number of sections is known
- **What you get**: Prevents unwanted extra pieces.
- **Limitations**: A wrong count merges the final sections.
### Output names

Prefix and format control the output names.

- **When to use**: When later steps rely on naming
- **What you get**: Script integration becomes easier.
- **Limitations**: Existing files can be overwritten.
## Installation and usage

### Check whether it is installed

```
csplit --version
```

sudo apt install coreutils   # Debian/Ubuntu
sudo dnf install coreutils   # Fedora

## Real-world examples

### Split by session

Start a new file at each START line.

```
csplit app.log '/^START/' '{*}'
```

### Split at a line

Split before line 100.

```
csplit notes.txt 100
```

### Limit sections

Split only twice.

```
csplit app.log '/^START/' '{2}'
```

---
Source (HTML): https://games.aidebatehub.com/programs/linux/basics/csplit.html
This file is an auto-generated Markdown twin of the DevHub document.