wiki-grav/pages/04.other/useful-commands/default.en.md
2023-07-29 15:37:39 +02:00

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---
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"
```
## Ghostscript
### Merge multiple PDF files
Ghostscript is preinstalled on a lot of Linux systems and can quite easily be used to merge and optimize multiple PDF files into one.
[shuser]
```sh
gs -q -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress -o merged.pdf <first>.pdf <second>.pdf
```
[/shuser]
> [Merge / convert multiple PDF files into one PDF](https://stackoverflow.com/a/19358402)
## 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.
## Arch Linux
### Detect AUR package rebuilds
Install the package `extra/rebuild-detector`
It will create a `pacman` hook to check which packages need to be rebuild, but can also be executed with the following command.
[shuser]
```sh
checkrebuild
```
[/shuser]
The packages might be rebuilt automatically a lot of the time, but sometimes it is necessary to for a rebuild using the AUR helper.
This is an example using `paru`
[shuser]
```sh
paru -S --rebuild=yes <package>
```
[/shuser]
## 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
```
### Find USB speed in use
First, the USB device you want to check has to be selected
[shuser]
```sh
lsusb
(out)Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
(out)Bus 003 Device 003: ID 0c45:652f Microdia Backlit Gaming Keyboard
(out)Bus 003 Device 002: ID 046d:c084 Logitech, Inc. G203 Gaming Mouse
(out)Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
(out)Bus 002 Device 002: ID 0781:55a3 SanDisk Corp. SanDisk 3.2Gen1
(out)Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
(out)Bus 001 Device 002: ID 2972:0047 FiiO Electronics Technology FiiO BTR5
(out)Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
```
[/shuser]
Now, using the ID, the USB class used can be determined
[shuser]
```sh
lsusb -d 0781:55a3 -v | grep bcdUSB
(out)bcdUSB 3.20
```
[/shuser]
### Change file modify time
Using `touch` it is possible to change the timestamps on a file.
_Note: The file has to be owned by the user executing the command_
Example changing the access and modify timestamps:
[shuser]
```
touch -a -m -t 202307291506.07 <file>
```
[/shuser]
```
-a: accessed time
-m: modified time
-t: timestamp - [[CC]YY]MMDDhhmm[.ss] time format
```
Alternatively to `-t` it is also possible to use `-d` for a looser format.
[ISO8061](https://en.wikipedia.org/wiki/ISO_8601) obviously works as well.
[shuser]
```
touch -a -m -d "2 hours ago" <file>
touch -a -m -d "2023-07-29T00:23" <file>
```
[/shuser]
> [Linux - modify file modify/access/change time](https://stackoverflow.com/questions/40630695/linux-modify-file-modify-access-change-time)
> [How can I change the date modified/created of a file?](https://askubuntu.com/questions/62492/how-can-i-change-the-date-modified-created-of-a-file)
### Create a random temporary directory / file
Using `mktemp`, a randomly named file or directory will be created in `/tmp`
Create a file:
[shuser]
```sh
mktemp
```
[/shuser]
Create a directory:
[shuser]
```sh
mktemp -d
```
[/shuser]
Save the output into an environment variable for future referencing
sh / Bash:
[shuser]
```sh
export TMPDIR=$(mktemp -d)
```
[/shuser]
Fish:
[shuser]
```fish
set TMPDIR (mktemp -d)
```
[/shuser]