Navigating the System

Basic Commands

In this, we’ll learn about:

• Windows
  • GUI (Graphical User Interface)
  • CLI (Command Line Interface)
• Linux
  • Command
  • Shell

    The CLI interpreter on Linux is called a shell, and the language that we’ll use to interact with this shell is called Bash.

List Directories in a GUI

• On Windows, filesystems are assigned to drive letters, which look like C:, or D:, or X:.
• The parent/root directory of C: would be written *C:*, and the root directory of X: would be written *X:*.
• Subdirectories are separated by **.

Windows List Directories in CLI

• To list contents of C drive

  ls C:\
  

• To get help for specific command

  Get-Help <command name>
  

  • In case of, ls command,

  Get-Help ls
  

  • To get more detailed help

  Get-Help ls-full
  

• To see hidden files in a directory

  ls -Force C:\
  

Linux: List Directories

• To list the contents of root directory

  ls /
  

  • /bin: essential binaries for program
  • /etc: system configuration file
  • /home: Where user files and configs live
  • /proc: Contain information of currently running processes
  • /usr: Meant for user installed software
  • /var: Stores system logs and anything that constantly changing
• ls command has very useful flags too.

• To see available flags for ls

  ls --help
  

• man shows the manual pages.

  man <command>
  

• To see hidden files, and long listing

  ls -al
  

• You can hide a file by prepending a . in the start of the filename.

Flags

Similar to Windows command parameters, a flag is a way to specify additional options for a command.

Windows: Changing Directories in a GUI

Absolute path

An absolute path is one that starts from the main directory.

Relative path

A Relative path is the path from your current directory.

Windows: Changing Directories in the CLI

• To know where you are in the folder

  pwd
  

• To change the directory you’re in

  cd <path\to\the\directory>
  

• To go one level up

  cd ..
  

• Get to the $HOME directory

  cd ~
  

Windows: Making Directories in the & CLI

• To make a new directory

  mkdir <directory name>
  

• To make a directory with spaces in its name

  mkdir 'directory name'
  mkdir directory` name
  

Linux: Making Directories in Bash

• To make a directory with spaces in its name

  mkdir directory\ name
  mkdir 'directory name'
  

Windows: Command History

• To see the history of previous commands

  history
  

• To reverse-search through history, shortcut is <ctrl+r>

• To clean PowerShell palette

  clear
  

Windows: Copying Files & Directories

• To copy a file

  cp <Path\to\the\file\to\be\copied> <Path\to\the\directory\of\copying> 
  

  • To copy multiple file at once, Wildcard is used

      cp *.<common pattern> <path\to\where\copied>
    

• To copy a directory and its content

  cp <directory name> <Path\to\where\copied> -Recurse -Verbose
  

Wildcard

A character that’s used to help select files based on a certain pattern.

Linux: Copying Files & Directories

• To copy a directory

  cp <Directory/to/be/copied> <Path/where/to/be/copied>
  

File and Text Manipulation

Windows: Display File Contents

• To view the file contents

  cat <File Name>
  

• To view the file contents, one page at a time

  more <File Name>
  

• To see only part of the file contents

  cat <File Name> -Head <Number of Lines>
  

• To see only part of the file contents from the tail

  cat <File Name> -Tail <Number of Lines>
  

Linux: Display File Contents

• To see file’s contents, interactively

  less <File Name>
  

• more has been abandoned in favor of more useful less command on Linux.

• To see only part of a file’s contents, head is used, which by default only shows first 10 lines

  head <File Name>
  

• To see only part of file’s contents, tail is used, which by default only shows last 10 lines

  tail <File Name>
  

Windows: Modifying Text Files

• To modify file’s contents from a CLI

  start notepad++ <File Name>
  

Windows PowerShell

• PowerShell is a powerful and complex command line language.

• To list directories, the real PowerShell command is can be found by:

  Get-Alias ls
  

so, to list directories

  Get-ChildItem <path\to\directory>

• Some old but not powerful as PowerShell, cmd.exe commands are

  

Windows: Searching within Files

• In GUI, Indexing Options applications are used.

• In command-line, search is done as:

  Select-String <Search String> <path\to\the\file>
  

• To search in multiple files at once

  Select-String <Search String> *.<file extension name>
  

Windows: Searching within Directories

• -Filter parameter is used with ls so search for particular files in a directory.
  • The -Filter parameter will filter the results for file names that match a pattern.

  ls <path\to\the\file> -Recurse -Filter *.exe
  

  • The asterisk means match anything, and the .exe is the file extension for executable files in Windows.

Linux: Searching within Files

• To search in files

  grep <Search String> <path/to/the/file>
  

• To search through multiple files at once

  grep <Search String> *.txt
  

Windows: Input, Output, and the Pipeline

  echo hello_word > hello.py

• The echo is an alias for PowerShell command Write-Output.
• Every Windows process and every PowerShell command can take input and can produce output. To do this, we use something called I/O streams or input output streams.
• I/O streams are
  • stdin
  • stdout
  • stderr
• The symbol > is something we call a Redirector operator that let us change where we want our stdout to go.

• The symbol » is used to not create a new file, just append the stdout

  echo 'Hello Planet' >> hello.py
  

• | Pipe operator is used to redirect the stdout of one command to stdin of another command.

  cat hello.py | Select-String planet
  

• To put new stdout to a new file.

  cat hello.py | Select-String pla > planet.txt
  

• If we don’t want to see error in CLI, to get them in a file

  rm secure_file 2> error.txt
  

  • All the output streams are numbered, 1 is for stdout and 2 for stderr

• If we don’t care about error messages and don’t want to save them in a file, we can redirect them to a null variable (a black hole for stderr)

  rm secure_file 2> $null
  

Linux: Input, Output, and the Pipeline

• On Linux, stdin operator can be used via symbol <.

  cat < SomeFile.py
  

  • Here we are using < operator for file input instead of keyboard input.

• To redirect error message to a file

  ls /dir/fake_dir 2> error_output.txt
  

• To filter out error message completely without saving

  ls /dir/fake_dir 2> /dev/null
  

Windows and Linux Advanced Navigation

• For more advance navigation, regex is used.

Regular expression (Regex)

Used to help you do advance pattern-based selections.