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Linux Shell Introduction

Command Anatomy


command [option] arguement
binary how to run what to run against
ls
ls -l
ls -lah /etc
  1. Command - program being run
  2. Option - how to operate ( dash and letter, stacking, --longer-options )
  3. Argument - what to operate on (like a filepath)

Key Differences

There are some important differences to note when coming from a Windows environment:

  1. Everything is a file

    • Ordinary Files
    • Directories
    • Special Files - hard / soft links etc.

  2. CaSe sEnSiTiVe!

    • "logfile.txt" is not the same as "Logfile.txt"

  3. /// FORWARD /// slashes

    • backslashes are used, but a more advanced topic

  4. File extensions don't matter

    • not required, but best practice to use

File System

/bin        binaries (points to /usr/bin)
/sbin       admin binaries programs
/dev        external devices are mounted (optical / hdd / ssd )
/etc        system and application configuration files
    elasticsearch/
    kibana/
    logstash/
/home       place for all user profile ~
/lib        libraries of code
/tmp        temporary "permissions free" working space
/var        various files system uses
/var/log    logged events
/usr/       user apps / tools / libraries
/opt        optional binaries

Absolute and Relative Paths

There are two types of filepaths when working in the terminal:

  1. Absolute

    • full path starting at root ( / )
    • path that always begins at / (root) i.e. very “top” of filesystem
    • bottom line: if it starts with a “ / “ it’s an absolute file path
    • example: /home/user/Documents/my-project

  2. Relative

    • relative to your current location in file system
    • example: ./Documents/my-project

Getting Help

Let's talk about how to help yourself. Here are some basic commands to get your bearings and help answer the basic questions of terminal life:

Surroundings

  • whoami - print the current user id and name
  • hostname - print or change system hostname
  • date - display or change date and time
  • uname - print general system information
  • cat /etc/*-release - print out OS information
  • which - Search user $PATH for program

Man Pages (RTFM)

The man pages are built-in documentation and user manual. Your box is packed full of them, so the trick is that it just takes patience and being able to search for what your looking for.

Let's look at an example workflow to get more information on how to use your current bash shell session:

  • man bash - opens the paginated manual
  • <spacebar> - jump to next page
  • f / b - forward / back
  • u / d - up / down
  • /<search_string> - search for a keyword
  • n(ext) / shift + n - forward and back
  • q - quit