213 lines
4.5 KiB
Markdown
213 lines
4.5 KiB
Markdown
---
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title: "Useful Commands"
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visible: true
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---
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[toc]
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## Imagemagick
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### Splitting PDF files
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```sh
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convert -density 600 {INPUT.PDF} -crop 50x100% +repage {OUT.PDF}
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```
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```
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-density: adjusts the quality of the resulting pdf. Higher values look better, but take longer to process
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-crop 50x100%: this splits the pdf into "left" and "right". 100x50% would split into "top" and "bottom"
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```
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## Ghostscript
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### Merge multiple PDF files
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Ghostscript is preinstalled on a lot of Linux systems and can quite easily be used to merge and optimize multiple PDF files into one.
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[shuser]
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```sh
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gs -q -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress -o merged.pdf <first>.pdf <second>.pdf
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```
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[/shuser]
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> [Merge / convert multiple PDF files into one PDF](https://stackoverflow.com/a/19358402)
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## Find
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### Change filtered permissions
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Using find with its `exec` switch one can set different permissions based on the usual find filters.
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One example would be only changing file or directory permissions.
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```sh
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find (directory) -type f -exec chmod 744 {} +
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```
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Replacing `-type f` with `-type d` would execute the `chmod` for directories instead.
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## Arch Linux
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### Detect AUR package rebuilds
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Install the package `extra/rebuild-detector`
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It will create a `pacman` hook to check which packages need to be rebuild, but can also be executed with the following command.
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[shuser]
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```sh
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checkrebuild
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```
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[/shuser]
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The packages might be rebuilt automatically a lot of the time, but sometimes it is necessary to for a rebuild using the AUR helper.
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This is an example using `paru`
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[shuser]
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```sh
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paru -S --rebuild=yes <package>
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```
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[/shuser]
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## Various
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### Overwrite disk with pseudorandom data
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Using openssl on CPUs with AES acceleration one can create pseudorandom data with high speeds.
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Much faster than `/dev/urandom` at least
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```sh
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openssl enc -aes-128-ctr -md sha512 -pbkdf2 -nosalt -pass file:/dev/urandom < /dev/zero | pv > {TARGET DISK}
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```
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Around 2GiB/s on my Ryzen 7 1700x if output to `/dev/null`
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### Formatted csv in terminal
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> [From Pretty CSV viewing on the Command Line](https://www.stefaanlippens.net/pretty-csv.html)
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```sh
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column -t -s, < {FILE.CSV}
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```
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### Download directory from webdav
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Using `wget`, it's possible to download directories recursively from WebDAV.
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```sh
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wget -r -nH -np --cut-dirs=1 --user={USERNAME} --password={PASSWORD} https://WEBDAVHOST/DIR/DIR
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```
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### Find USB speed in use
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First, the USB device you want to check has to be selected
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[shuser]
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```sh
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lsusb
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(out)Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
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(out)Bus 003 Device 003: ID 0c45:652f Microdia Backlit Gaming Keyboard
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(out)Bus 003 Device 002: ID 046d:c084 Logitech, Inc. G203 Gaming Mouse
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(out)Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
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(out)Bus 002 Device 002: ID 0781:55a3 SanDisk Corp. SanDisk 3.2Gen1
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(out)Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
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(out)Bus 001 Device 002: ID 2972:0047 FiiO Electronics Technology FiiO BTR5
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(out)Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
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```
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[/shuser]
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Now, using the ID, the USB class used can be determined
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[shuser]
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```sh
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lsusb -d 0781:55a3 -v | grep bcdUSB
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(out)bcdUSB 3.20
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```
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[/shuser]
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### Change file modify time
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Using `touch` it is possible to change the timestamps on a file.
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_Note: The file has to be owned by the user executing the command_
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Example changing the access and modify timestamps:
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[shuser]
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```
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touch -a -m -t 202307291506.07 <file>
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```
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[/shuser]
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```
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-a: accessed time
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-m: modified time
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-t: timestamp - [[CC]YY]MMDDhhmm[.ss] time format
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```
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Alternatively to `-t` it is also possible to use `-d` for a looser format.
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[ISO8061](https://en.wikipedia.org/wiki/ISO_8601) obviously works as well.
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[shuser]
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```
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touch -a -m -d "2 hours ago" <file>
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touch -a -m -d "2023-07-29T00:23" <file>
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```
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[/shuser]
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> [Linux - modify file modify/access/change time](https://stackoverflow.com/questions/40630695/linux-modify-file-modify-access-change-time)
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> [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)
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### Create a random temporary directory / file
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Using `mktemp`, a randomly named file or directory will be created in `/tmp`
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Create a file:
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[shuser]
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```sh
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mktemp
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```
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[/shuser]
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Create a directory:
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[shuser]
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```sh
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mktemp -d
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```
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[/shuser]
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Save the output into an environment variable for future referencing
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sh / Bash:
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[shuser]
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```sh
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export TMPDIR=$(mktemp -d)
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```
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[/shuser]
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Fish:
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[shuser]
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```fish
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set TMPDIR (mktemp -d)
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```
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[/shuser]
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