Linux
Linux (ˈlinʊks) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds.

• etc: system-wide configuration folder (eg. pacman mirrorlist)
• bin: common binary files for applications (eg. ls)
• boot: stores my bootloader
• lib: shared libraries that applications use
• mnt: where external drives are mounted (eg. usbstick)
• opt: manually installed softwares
• proc: information about system processes and resources, each folder is a process' PID.
• root: volatile storage
• srv: service directory, where service data is stored
• sys: it's a way to interact with the hardware
• tmp: where files are temporary stored in a session (eg. writing in a libreoffice file)
• usr: user application's space, where applications will be installed
• var: contains files that are supposed to grow (eg. logs)
• home: where you store your own personal files

Instead of retyping a long list of arguments of a mispelled command, we can correct whatever typo we made with ^typo^correct

$ dc /tmp

$ ^dc^cd

We can use shell expansion to:

• rename and backup operations
• pattern matching
• match any string

• & (Ampersand Operator)

  run one or more jobs in the background,

  EXAMPLE: ping www.google.com & apt-get update & apt-get upgrade &

  • Ctrl-z pauses the job
  • jobs prints all the jobs

• ; (Semi-colon operator)

  run several commands at once sequentially, disregarding the exit status of the preceding command

  EXAMPLE: apt-get update ; apt-get upgrade ; mkdir test

• && (AND operator)

  executes a command IF the exit status of the preceding command is 0

  EXAMPLE: ping www.google.com && links www.google.com (checking the connection before using links command)

• || (OR operator)

  much like an 'else' statement, allows to execute the second command only if the execution of the first fails (i.e., the exit status is 1)

  EXAMPLE: apt-get update || links www.google.com

• ! (NOT operator)

  much like an 'except' statement, this command will execute all except the condition provided

  EXAMPLE: rm -r !(*.html) removes all files in a folder except .html files

• | (PIPE operator)

  passes the output of the first command to the second one

  EXAMPLE: ls -l | less

• {} (Command Combination operator)

  combine two or more commands

  [ -d Folder] || { echo creating Folder; mkdir Folder; } && echo Folder exists.

• grep (Globally search for a Regular Expression and Print) for searching stuff in files, or any STDOUT (eg. 'ls' command)

  EXAMPLE: ls | grep "\.exe$"

• sed (stream editor) for substitituing, deleting or filtering text on a stream

  EXAMPLE: sed 's/regexp/replacement/g' file > output

  -r will extend the Regex portability (POSIX)

• xargs (command args) pass any command to it and it will execute it on a stream.

  EXAMPLE: find | grep "\.exe$" | xargs ls -lh

Steps to free disk space on your Linux machine:

1. Check directories disk space: cd / && sudo du -h --max-depth=1
2. Delete pacman cache:
   • sudo paccache -r keep at least 3 caches
   • sudo paccache -rk 1 keep only 1 pkg cache