---
title: sed — stream text substitution
date: 2026-10-18
time: 12:00
model: admin
category: programs
author_type: human
summary: A tool that replaces or deletes specific strings without opening the file. Useful for making batch configuration changes.
tags: program, Automation and scheduled tasks, sed
---

**💬 "sed command"**

sed processes text as a stream to perform substitution and deletion. It is often used for batch changes to configuration files.

-i modifies files directly; to avoid mistakes, it is best to use a backup extension as well.

- **Concept**: Replaces or deletes matching parts of an input stream.
- **s///**: The basic form of the substitution command.
- **-i**: Modifies files directly.
- **-n + p**: Prints only specific lines.
## Commonly used options

| Option | Description |
| --- | --- |
| -i.bak | Backs up the original to .bak before modification |
| s/old/new/g | Replaces all matches |
| -E | Uses extended regular expressions |
| -n '/pattern/p' | Prints only lines matching the pattern |

## 3 essential command combinations

- `sed -i.bak 's/10.0.0.5/10.0.0.9/g' /etc/app/config.yml` — Batch-change IPs in a configuration (with backup)
- `sed -n '/^server_name/p' /etc/nginx/nginx.conf` — Extract only specific configuration lines
- `sed '/^#/d;/^$/d' /etc/app/config.yml | head` — Remove comments and blank lines for viewing
**💬 "Create an example that includes how to undo this operation"**

Here are common situations on production servers, organized step by step.

### Step 1 · Check the current value

Check the target string before changing it.

```
grep -n '10.0.0.5' /etc/app/config.yml
```

### Step 2 · Replace (with backup)

Use -i.bak to keep the original while replacing.

```
sed -i.bak 's/10.0.0.5/10.0.0.9/g' /etc/app/config.yml
```

### Step 3 · Verify

Check the result and confirm the service reflects it.

```
grep -n '10.0.0.9' /etc/app/config.yml && systemctl restart myapp
```

## In practice, this is how it is used

### 1. Replace configuration IPs

**Scenario** — Change IPs in the configuration due to a database server migration.

```
sed -i.bak 's/10.0.0.5/10.0.0.9/g' /etc/app/config.yml
```

**Result** — All references are changed to the new IP, and the original remains in .bak.

**Key point** — Check the number of matches with grep before replacing to avoid omissions or over-replacement.

### 2. Compare settings by removing comments

**Scenario** — You want to see only the settings that actually apply.

```
sed '/^#/d;/^$/d' /etc/nginx/nginx.conf | head -30
```

**Result** — You see the actual settings with comments and blank lines removed.

**Key point** — Because the original is not modified, you can check safely.

## Things to watch out for

- -i modifies files directly. Always include a backup extension.
- If the string to replace contains /, change the delimiter (e.g., s|a|b|g).
- Regular expression special characters need to be escaped.
## Actual execution output

This is the result of batch-replacing configuration IPs with a backup and verifying them.

![sed command execution result: batch configuration replacement](https://games.aidebatehub.com/assets/sed-demo.png)

Actual production server

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