The Shell

Stream Manipulation

Standard I/O
- stdin: standard input
- stdout: standard output
- stderr: standard error
COMMAND > FILE: takes the stdout and writes it to the file
- 2> writes stderr to file
- >> appends instead of overwriting file contents
COMMAND < FILE: takes the contents of the file and sends it as input to the command
COMMAND_1 | COMMAND_2: the pipe character, which takes the stdout of the left command and moves it to stdin for the right command
- stdin input is NOT the same as sending arguments to command! Some commands will have functionality to take file arguments and read its contents, or to take in contents of stdin
tee FILE: takes input and write it to file and stdout

Useful Commands

cd -: changes directory to the one you were at previously, i.e. a back button
pushd, popd: generate/prune a directory stack as you move between directories
which PROGRAM: shows the absolute path to the program being called
man PROGRAM: the manual command, a more readable -h or --help
sudo: “do as su (super user)”
- sudo su: creates a super user terminal instance, which you’ll notice looks like root@DEVICE:PATH# instead of USER@DEVICE:PATH$
xdg-open FILE: open file in appropriate application

Linux Filesystem

Uses for different directories in /:
- /bin = essential command binaries
- /sbin = essential system binaries, usually to be run by root
- /dev = device files, special files that often are interfaces to hardware devices
- /etc = host-specific system-wide configuration files
- /home = home directories for users in the system
- /lib = common libraries for system programs
- /opt = optional application software
- /sys = contains information and configuration for the system
- /tmp = temporary files (also /var/tmp). Usually deleted between reboots.
- /usr/ = read only user data
  - /usr/bin = non-essential command binaries
  - /usr/sbin = non-essential system binaries, usually to be run by root
  - /usr/local/bin = binaries for user compiled programs
- /var = variable files like logs or caches