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
```

For more advance navigation, regex is used.

Regular expression (Regex)

Used to help you do advance pattern-based selections.