powershell-shell-detection

# PowerShell Shell Detection & Cross-Shell Compatibility

Critical guidance for distinguishing between PowerShell and Git Bash/MSYS2 shells on Windows, with shell-specific path handling and compatibility notes.

## Shell Detection Priority (Windows)

When working on Windows, correctly identifying the shell environment is crucial for proper path handling and command execution.

### Detection Order (Most Reliable First)

1. **process.env.PSModulePath** (PowerShell specific)
2. **process.env.MSYSTEM** (Git Bash/MinGW specific)
3. **process.env.WSL_DISTRO_NAME** (WSL specific)
4. **uname -s output** (Cross-shell, requires execution)

## PowerShell Detection

### Primary Indicators

**PSModulePath (Most Reliable):**
```powershell
# PowerShell detection
if ($env:PSModulePath) {
    Write-Host "Running in PowerShell"
    # PSModulePath contains 3+ paths separated by semicolons
    $env:PSModulePath -split ';'
}

# Check PowerShell version
$PSVersionTable.PSVersion
# Output: 7.5.4 (PowerShell 7) or 5.1.x (Windows PowerShell)
```

**PowerShell-Specific Variables:**
```powershell
# These only exist in PowerShell
$PSVersionTable    # Version info
$PSScriptRoot      # Script directory
$PSCommandPath     # Script full path
$IsWindows         # Platform detection (PS 7+)
$IsLinux           # Platform detection (PS 7+)
$IsMacOS           # Platform detection (PS 7+)
```

### Shell Type Detection in Scripts

```powershell
function Get-ShellType {
    if ($PSVersionTable) {
        return "PowerShell $($PSVersionTable.PSVersion)"
    }
    elseif ($env:PSModulePath -and ($env:PSModulePath -split ';').Count -ge 3) {
        return "PowerShell (detected via PSModulePath)"
    }
    else {
        return "Not PowerShell"
    }
}

Get-ShellType
```

## Git Bash / MSYS2 Detection

### Primary Indicators

**MSYSTEM Environment Variable (Most Reliable):**
```bash
# Bash detection in Git Bash/MSYS2
if [ -n "$MSYSTEM" ]; then
    echo "Running in Git Bash/MSYS2: $MSYSTEM"
fi

# MSYSTEM value