shell

Operators Link to heading

|: pipes the standard output (stdout) of the left command into the standard input of the right one
|&: pipes stdout and stderr in the standard input of the right command
&&: executes the right command if the left one succeeded
||: executes the right command if the left one failed

General Link to heading

Find out linux version

cat /etc/os-release

Find out current user and its groups:

whoami  # shows current user
groups # shows groups of current user
groups <user>  # shows groups user belongs to

gentent group # list all groups
getent group <group> # shows members of a group

# add user to an additional group
sudo usermod -aG <group> <user>
# -a: append, otherwise user will be removed from all not listed groups
# -G: takes a comma separated list of groups

Reboot / shutting down

reboot

Updating packages on Ubuntu

sudo apt-get update
sudo apt-get upgrade # upgrades all packages that can be upgraded without breaking other packages

Managing environment variables

# setting env variable
export https_proxy=http://<user>:@<proxy_address>:8080
# removing env variable
unset https_proxys
# showing env variables
printenv

Commands Link to heading

TODO: df # total used and available disk space
TODO: nohup
TODO: tail -n 200 some.log
- tail -f some.log
chmod: changing rights
3 numbers: _ _ _ -> permission for user, group, others
- parameters:
  permission symbol number
  read r 4
  write w 6
  execute x 1
  permissions add up: 6 = 4 + 2: read and write access
```
chmod 400 private-key-file.pem  # restricting file access (read) to yourself
chmod +x some_script.py  # make a file executable
```
du:
- get the size of a folder: du -hs /path/to/directory
  - s: gives only the summary of the folder, not for every folder separately
  - h: human readable size in MiB or GiB instead of exact KiB
grep:
- i: case-insensitive search e.g. to search environment variables env | grep -i proxy
- use regex: e.g. select the lines that contain either “hook id:” or “duration:”:
```
grep -E '(hook id:|duration:)' pre-commit-logs.txt
```

permission	symbol	number
read	r	4
write	w	6
execute	x	1

ln: command used to create links between files

s: create a symbolic (soft) link rather than a hard link

# creating a symlink
ln -s <path to real file e.g. ~/dotfiles/ghostty/config> <where the symlink should be created e.g. ~/.config/ghostty/config>

# checking a symlink
ls -l <path to symlink>

rm:

rm *   # delete all files (no directories) in the current working directory
rm -rf *  # delete all files + directories recursively

Custom function Link to heading

# in .zshrc
start_ec2() {
  export AWS_DEFAULT_REGION=eu-central-1
  export AWS_PROFILE=<AWS profile name>
  aws ec2 start-instances --instance-ids <instance id>
}

# use the command
start_ec2