---
title: "Useful Commands"
visible: true
---

[toc]

## Imagemagick

### Splitting PDF files

```sh
convert -density 600 {INPUT.PDF} -crop 50x100% +repage {OUT.PDF}
```

```
-density: adjusts the quality of the resulting pdf. Higher values look better, but take longer to process
-crop 50x100%: this splits the pdf into "left" and "right". 100x50% would split into "top" and "bottom"
```

## Find

### Change filtered permissions

Using find with its `exec` switch one can set different permissions based on the usual find filters.  
One example would be only changing file or directory permissions.

```sh
find (directory) -type f -exec chmod 744 {} +
```

Replacing `-type f` with `-type d` would execute the `chmod` for directories instead.

## Various

### Overwrite disk with pseudorandom data

Using openssl on CPUs with AES acceleration one can create pseudorandom data with high speeds.  
Much faster than `/dev/urandom` at least

```sh
openssl enc -aes-128-ctr -md sha512 -pbkdf2 -nosalt -pass file:/dev/urandom < /dev/zero | pv > {TARGET DISK}
```

Around 2GiB/s on my Ryzen 7 1700x if output to `/dev/null`

### Formatted csv in terminal

> [From Pretty CSV viewing on the Command Line](https://www.stefaanlippens.net/pretty-csv.html)

```sh
column -t -s, < {FILE.CSV}
```

### Download directory from webdav

Using `wget`, it's possible to download directories recursively from WebDAV.

```sh
wget -r -nH -np --cut-dirs=1 --user={USERNAME} --password={PASSWORD} https://WEBDAVHOST/DIR/DIR
```