Shells

About

  • A command interpreter allowing interaction with the OS.

  • Processes typed commands and executes programs.

  • When you open a terminal, the shell is the program that receives your commands.

Windows: Shells without native support

  • Some shells are not natively supported, but can be used on Windows through:

    • WSL .

    • Msys2 .

    • GitBash .

    • CygWin .

  • This also applies to TMux .

No Shell

win32 API

Create Processes

  • CreateProcessW

File Association

  • Use ShellExecuteEx  or ShellExecuteW , to open files by association (e.g., foo.pdf  with Acrobat).

  • CreateProcess  does not handle file associations.

UAC Elevation

  • CreateProcessW  runs with the caller’s token. It will not trigger UAC elevation.

  • To elevate use ShellExecuteEx  with runas  or use CreateProcessWithTokenW  / CreateProcessAsUser  with the right token.

"Conveniences" you lose by not using a shell

  • Built-ins :

    • Will not run dir , cd , or other cmd.exe  built-ins. Those are implemented inside the shell.

  • .bat / .ps1 files :

    • *.bat , *.cmd , .ps1  are not native executables.

    • *.bat  must be run by cmd.exe cmd.exe /c yourscript.bat  (or use the shell).

    • *.ps1  must be run by PowerShell (or invoked via pwsh -File ).

  • Pipes :

    • This refers to the usage of something like:

      • >

        • cmd.exe: Redirect stdout to a file (overwrite).

        • powershell: Redirect stdout to a file (overwrite).

      • |

        • cmd.exe: byte-stream pipe.

        • powershell: object pipeline.

    • You must create pipes yourself and wire STARTUPINFO.hStdInput / hStdOutput  and bInheritHandles .

    • You control the environment block and current directory. If you want inherited handles or specific stdio redirection you must set those in STARTUPINFO  and use bInheritHandles .

    • Odin does this with the win32  api by: 

    &win32.STARTUPINFOW{
    cb = size_of(win32.STARTUPINFOW),
    hStdError  = stderr_handle,
    hStdOutput = stdout_handle,
    hStdInput  = stdin_handle,
    dwFlags = win32.STARTF_USESTDHANDLES,
},

  • Conditionals :

    • This refers to the usage of something like:

      • ||

        • cmd.exe: run RHS if LHS fails.

        • powershell: run RHS if LHS fails.

      • &&

        • cmd.exe: run RHS if LHS success.

        • powershell: run RHS if LHS success.

    • Parent or shell must implement conditional logic. Parent must check exit code and decide.

  • Sequence invoke :

    • This refers to the usage of something like:

      • &

        • cmd.exe: Command operator. Runs next command unconditionally.

      • ;

        • powershell: Command operator.

    • If you want sequencing invoke multiple CreateProcessW  calls or implement sequencing logic in your program.

Shells

Commands from tools

Help

  • tldr :

    • tldr

View Directory Contents

  • eza :

    • l

    • l2

    • l3

    • lr

    • ll

  • fzf :

    • fd

      • find dir

    • ff

      • find file

Change Directory

  • zoxide

    • z

cmd.exe

  • OSs :

    • Windows.

    • Default on macOS since 2019.

  • Older Windows shell, present since Windows NT.

  • Limited compared to PowerShell, no support for advanced scripts.

Tokens

  • |

    • Byte-stream pipe.

    • Stdout of left goes to stdin of right.

    • The shell creates an anonymous pipe and sets child std handles.

  • |>

    • Not a thing.

  • >

    • Redirect stdout to a file (overwrite).

  • 2>

    • Redirects stderr.

  • >>

    • Appends.

  • ||

    • Run RHS only if LHS exit code != 0 (failure).

  • &&

    • Run RHS only if LHS exit code == 0 (success).

  • ;

    • Not a thing.

    • Treated as a literal character unless quoted or part of a command argument.

  • &

    • Command separator. Runs next command unconditionally.

Commands

  • help

  • cls

    • Clears the terminal

  • cd  / chdir

    • Change Directory

  • dir

    • See contents of directory ( ls  equivalent).

  • cat <file>  / type <file>

    • Sees the content of the file.

  • mkdir <dir>

    • Create directory

  • del <file>

    • Remove files.

  • copy NUL <file>

    • Create empty file.

  • rmdir /s /q <dir>

    • Remove directory.

    • I'm not sure about the flags.

  • move <from> <to>

    • Move file.

  • copy <from> <to>

    • Copy file.

  • rename <old> <new>

    • Rename file.

  • find <text> <file>

    • Find in file.

  • start <file>

    • Opens IN Explorer.

  • explorer

    • Opens THE Explorer.

  • systeminfo

    • System information.

    • CPU-Z and GPU-Z are better.

    • Doesn't show much.

  • ipconfig

PowerShell

  • OSs :

    • Windows.

  • Replaces Command Prompt as Microsoft’s official tool.

  • Based on .NET, supports objects  instead of just text.

  • Can run traditional Windows commands ( dir , ipconfig ) and advanced scripts ( .ps1 ).

Configuration

  • $PROFILE

    • Shows the desired path for the configuration file.

Tokens

  • |

    • Object pipeline. Cmdlets pass .NET objects (not raw bytes). When external programs are involved PowerShell passes text through std streams.

  • |>

    • Forward-pipe operator in PowerShell 7+. It passes the left-hand value as the first argument to the right-hand command or script block.

    • Different from |  which is an object pipeline.

  • >

    • Redirect stdout to a file (overwrite).

  • 2>

    • Redirects stderr.

  • >>

    • Appends.

  • ||

    • Conditional OR in PowerShell 7+, running RHS if LHS failed.

  • &&

    • Conditional AND in PowerShell 7+, running RHS if LHS sucess.

  • ;

    • Command separator.

    • Example: Get-Process; Get-Service  runs both commands sequentially.

  • &

    • Call operator, used to invoke a command, script, or scriptblock stored in a variable or string.

    • Example: & 'C:\script.ps1' .

Commands

  • help

  • cls  / clear

    • Clears the terminal

  • ls  / gci  ( Get-ChildItem ) / dir

    • See contents of directory.

  • cd  / chdir  / sl  ( Set-Location )

    • Change Directory

  • mkdir  / ni

    • Create directory

    • If the file doesn't exist, it creates it.

    • Does not update the modification date of an existing file.

  • del

    • Remove files or directories

  • cat

    • Sees the content of the file.

  • start

    • Opens IN Explorer.

  • explorer

    • Opens THE Explorer.

  • systeminfo

    • System information.

    • CPU-Z and GPU-Z are better.

    • Doesn't show much.

  • ipconfig

NuShell

  • NuShell .

    • It was recommended to me.

    • Crossplatform, Rust.

Starship

  • OSs :

    • Windows

    • Linux.

    • MacOS.

      • Default on macOS since 2019.

  • Features :

    • Written in Rust.

    • Supposedly better than Zsh.

  • Impressions :

    • Cross-platform is nice.

    • Nice customization.

    • Nice.

    • Cool.

Bash (Bourne Again Shell)

  • OSs :

    • ~Windows (no native support)

    • Linux

      • Default in most Linux distributions.

    • MacOS.

  • Supports scripts, variables, loops, and customization via ~/.bashrc .

  • To check if using Bash: 

    echo $SHELL

    • If output is /bin/bash , you are using Bash.

Commands

  • man

    • [man]ual in Linux.

  • ls

    • See contents of directory.

  • cat

    • See contents of file.

  • cls  / clear

  • cd

    • Change directory.

  • pwd

    • Shows current directory.

  • touch

    • If the file doesn't exist, it creates it.

    • If the file already exists, it updates the modification date without altering the content.

  • rm <file>

    • Remove file.

  • mkdir <dir>

    • Make directory.

  • rm -r <dir>

    • Remove directory.

  • cp <from> <to>

    • Copy file.

  • mv <old> <new>

    • Rename file.

  • grep <text> <file>

    • Find in file.

  • ps

    • Show processes.

  • kill <PID>

    • Kill a process.

Zsh (Z Shell)

  • Zsh config .

  • OSs :

    • ~Windows (no native support)

    • Linux.

    • MacOS.

      • Default on macOS since 2019.

  • More powerful than Bash.

  • Advanced autocompletion and command suggestions.

  • Better support for plugins and themes , with frameworks like Oh My Zsh .

  • Supports advanced globbing ( **/*.txt  finds all .txt  files in subfolders).

  • Install on Linux : 

    sudo apt install zsh     # Debian/Ubuntu
sudo pacman -S zsh       # Arch Linux
sudo dnf install zsh     # Fedora

    • Make default: 

      chsh -s $(which zsh)
Themes

Fish (Friendly Interactive Shell)

  • OSs :

    • ~Windows (no native support).

    • Linux

    • macOS

  • Extremely easy to use and interactive.

  • Automatic command suggestions with history.

  • Syntax more intuitive than Bash/Zsh.

  • Incompatible with Bash scripts, may cause issues for advanced users.

  • To install: 

    sudo apt install fish     # Debian/Ubuntu
sudo pacman -S fish       # Arch Linux
sudo dnf install fish     # Fedora

  • To test: 

    fish

GitBash

  • Based on MinGW.

  • Comes with 'Git for Windows', allowing use of Unix commands ( ls , grep , vim ).