Lesson 3: Shell Navigation

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The Shell

A shell is a text-based user-interface for a computer.
sea shell

Shell Examples

Required by all POSIX Operating Systems.
Default on most GNU/Linux-based Operating Systems.
Default shell on most BSD (Unix) based Operating Systems
Useful but not sh compliant shell.
The hip new shell on the block.

Basic Shell Commands

$ pwd    # Prints the current working directory (where you are)
$ ls     # Prints the contents of the current working directory
$ cd <path/to/other/directory>   # Navigates to a new directory.
$ echo "some thing $AND_VARS"    # Prints a string to the screen.
$ cat  foo.txt bax.txt # Prints the contents of a file(s) to the screen.
$ grep foo file.txt    # Searches `file.txt` for the string `foo`
$ less  file.txt       # Prints a file to the screen so you can arrow up/down.
$ env    # Prints environment variables to the screen.
$ whoami # Prints out current user
$ help   # When in doubt, always type help.

Shell Scripts


if [ $(whoami) == "root" ]; then
  echo "You're root!"
  echo "Your username is $(whoami)"
  echo "Your home-directory is $HOME"
  echo "Your current directory is $PWD"
  echo "Your computer's host-name is $HOSTNAME"

Invoke with:

$ chmod +x about_me.sh  # Tell Linux that this can be run as a program.
$ ./about_me.sh         # Invoke the script.

File Paths

The current directory.
The parent directory.
Alias for your home directory.

Separates directories: one_dir/another_dir/last_dir

Alone, or at the start of a path, it is the root directory.

File Paths

$ tree -F
|-- bar/
|   |-- one
|   `-- two
|-- baz/
`-- foo/
    `-- a/
        `-- b/

5 directories, 2 files

Special Characters

Wildcard (*)

Used as a stand-in for any character(s).

Example: cat *.log cats all files in the current working directory ending in .log.

End of line ($)
Used to specify the end of a regex. We'll cover what regex is later.
Curl braces ({ })

Used to specify a set.

Example: ls {foo,bar,baz}ley-thing expands to ls fooley-thing barley-thing bazley-thing

Escape special characters (treat them as normal characters) with the escape character (\).

Type Less, Tab More

Pressing the tab key auto-completes a command, file-path, or argument in your shell.

Pressing tab multiple times completes the command to the best of the shells ability and then lists the possible completions (if there are any).

$ ls b    # <tab>
$ ls ba   # <tab>
bar_thing/ baz_thing/
$ ls bar  # <tab>
$ ls bar_thing


Further Reading

BASH Programming - Introduction HOW-TO
A free online resoruce of learning bash programming. Covers some concepts we'll get to later in DOBC, but a good resoruce to have on hand.
Running rm -rf / on Linux
This video demonstrates what happens when you 'delete your hard-drive' on Linux. A fun watch!