Code Layout & Formatting

These guidelines are about readability. Some of them are arbitrary rules, but they are based on decades of traditions in programming, so while you may disagree with some rules (and should always follow the rules of individual projects), when we ask you to leave an empty line after a closing function brace, or two lines before functions, we're not being capricious, we're doing so because it makes it easier for experienced developers to scan your code.

Maintain Consistency in Layout

Rules about indentation, line length, and capitalization are about consistency across code bases. Long practice has shown that it's easier to read and understand code when it looks familiar and you're not being distracted by details, which means that it's better for everyone in the community to follow a single set of rules.

We don't expect everyone to follow these guidelines, and rules for individual projects always trump these. Whether for legacy reasons, or to match guidelines for multiple languages in a single project, different projects may have different style guidelines. Since the goal is consistency, you should always abide by any style rules that are in place on the project you are contributing to.

If you do have a legacy project that is in source control and you decide to reformat code to adopt these rules, try to make all of your whitespace changes in a single commit that does nothing but edit the whitespace. You should never reformat the whitespace on a file as part of a content change because it makes the changes hard to spot.

Capitalization Conventions

PowerShell is not case sensitive, but we follow capitalization conventions to make code easy to read. They are based on the capitalization conventions Microsoft created for the .NET framework, since PowerShell is a .NET scripting language, and PowerShell cmdlets are primarily written in .NET languages following those guidelines.

Terminology
  • lowercase - all lowercase, no word separation
  • UPPERCASE - all capitals, no word separation
  • PascalCase - capitalize the first letter of each word
  • camelCase - capitalize the first letter of each word except the first.

PowerShell uses PascalCase for all public identifiers: module names, function or cmdlet names, class, enum, and attribute names, public fields or properties, global variables and constants, etc. In fact, since the parameters to PowerShell commands are actually properties of .Net classes, even parameters use PascalCase rather than camelCase.

PowerShell language keywords are written in lower case (yes, even foreach and dynamicparam), as well as operators such as -eq and -match. The keywords in comment-based help are written in UPPERCASE to make it easy to spot them among the dense prose of documentation.

function Write-Host {
    <#
    .SYNOPSIS
        Writes customized output to a host.
    .DESCRIPTION
        The Write-Host cmdlet customizes output. You can specify the color of text by using
        the ForegroundColor parameter, and you can specify the background color by using the
        BackgroundColor parameter. The Separator parameter lets you specify a string to use to
        separate displayed objects. The particular result depends on the program that is
        hosting Windows PowerShell.
    #>
    [CmdletBinding()]
    param(
        [Parameter(Position = 0, ValueFromPipeline = $true, ValueFromRemainingArguments = $true)]
        [PSObject]
        $Object,

        [Switch]
        $NoNewline,

        [PSObject]
        $Separator,

        [System.ConsoleColor]
        $ForegroundColor,

        [System.ConsoleColor]
        $BackgroundColor
    )
    begin {
    ...

As stated previously, PowerShell uses PascalCase for all public identifiers. Function names should follow PowerShell's Verb-Noun naming conventions, using PascalCase within both Verb and Noun.

A special case is made for two-letter acronyms in which both letters are capitalized, as in the variable $PSBoundParameters or the command Get-PSDrive. Note that (as specified in the .NET guidelines) this does not affect the commonly capitalized (but not acronym) words "OK" and "ID" . You should also not extend it to compound acronyms, such as when Azure's Resource Manager (RM) meets a Virtual Machine (VM) in Start-AzureRmVM...

We are aware that there are many places where these conventions have not been followed properly for various reasons -- you should consider these exceptions (such as for COM interop) or mistakes (such as System.Data.SqlClient.SQLDebugging), but not a reason for you to disregard the conventions.

If you wish, you may use camelCase for variables within your functions (or modules) to distinguish private variables from parameters, but this is a matter of taste. Shared variables should be distinguished by using their scope name, such as $Script:PSBoundParameters or $Global:DebugPreference. If you are using camelCase for a variable that starts with a two-letter acronym (where both letters are capitalized), both letters should be set to lowercase (such as adComputer).

One True Brace Style

This guide recommends the so-called "One True Brace Style" variant to K&R, which requires that every braceable statement should have the opening brace on the end of a line, and the closing brace at the beginning of a line.

There is one notable exception when passing small scriptblocks to parameters (where K&R would allow leaving off the braces entirely), we allow putting the entire statement on a single line.

enum Color {
    Black,
    White
}

function Test-Code {
    [CmdletBinding()]
    param(
        [int]$ParameterOne
    )
    end {
        if (10 -gt $ParameterOne) {
            "Greater"
        } else {
            "Lesser"
        }
    }
}

# An Exception case:
Get-ChildItem | Where-Object { $_.Length -gt 10mb }

The primary reason for this recommendation is practical: there are no exceptions necessary when following this rule, and when code is written following this style, new lines of code can be inserted between any two lines with no risk of accidentally breaking the code by separating braces from their statement blocks. Thus, it's easier to follow, and makes errors less likely.

Because this choice was somewhat contentious in the community (about 1/3 of voters opposed), it's worth adding some addition reasoning here: First: in some historical consoles, it was necessary to write this way, so much of the early PowerShell code follows this style anyway. Second: PowerShell functions which accept scriptblocks (such as ForEach-Object and Where-Object) are common, and an inherent part of the syntax of important PowerShell-based domain-specific languages such as DSC. Since it's required to place the opening brace on the end of the line in those cases, the only consistent option is to follow OTBS.

Always Start With CmdletBinding

All of your scripts or functions should start life as something like this snippet:

[CmdletBinding()]
param()
process {
}
end {
}

You can always delete or ignore one of the blocks (or add the begin block), add parameters and necessary validation and so on, but you should avoid writing scripts or functions without [CmdletBinding()], and you should always at least consider making it take pipeline input.

Prefer: param(), begin, process, end

Having a script written in the order of execution makes the intent clearer. Since there is no functional reason to have these blocks out of order (they will still be executed in the normal order), writing them out of order can be confusing, and makes code more difficult to maintain and debug.

More explicit code is more maintainable. While PowerShell allows leaving off the explicit name of the end block (and even has a filter keyword that converts the anonymous block to a process block), we recommend against using these features as it results in less explicit code.

Indentation

Use four spaces per indentation level

Usually you will press the [Tab] key to indent, but most editors can be configured to insert spaces instead of actual tab characters. For most programming languages and editors (including PowerShell ISE) the default is four spaces, and that's what we recommend. Different teams and projects may have different standards, and when contributing to a project, you should abide by the predominant style, of course.

function Test-Code {
    foreach ($exponent in 1..10) {
        [Math]::Pow(2, $exponent)
    }
}

Indenting more than 4-spaces is acceptable for continuation lines (when you're wrapping a line which was too long). In such cases you might indent more than one level, or even indent indent an odd number of spaces to line up with a method call or parameter block on the line before.

function Test-Code {
    foreach ($base in 1,2,4,8,16) {
        foreach ($exponent in 1..10) {
            [System.Math]::Pow($base,
                               $exponent)
    }
}

Maximum Line Length

Limit lines to 115 characters when possible.

Keeping lines to a small width allows scripts to be read in one direction (top to bottom) without scrolling back-and-forth horizontally. What, exactly, this width should be is a one of the favorite arguing points among developers on the internet (more splintered than emacs vs vi or gnu GPL vs MIT).

In this guide we use two particular sources for the maximum line width:

The PowerShell console is, by default, 120 characters wide, but it allows only 119 characters on output lines, and when entering multi-line text, PowerShell uses a line continuation prompt: >>> and thus limits your line length to 116 anyway.

Github's current maximum line width varies between 121 and 126 depending on your browser and OS (and thus, font). However, the 115 line length suggested by PowerShell would be enough to even allow side-by-side diffs to be displayed without scrolling or wrapping on the current "standard" 1080p monitor.

Again, this is a particularly flexible rule, and you should always follow the guidelines of projects when you're contributing to other people's projects. Although most of us work on widescreen monitors, not everyone can see well without magnification or extremely large fonts.

The preferred way to avoid long lines is to use splatting (see Get-Help about_Splatting) and PowerShell's implied line continuation inside parentheses, brackets, and braces -- these should always be used in preference to the backtick for line continuation when applicable, even for strings:

Write-Host -Object ("This is an incredibly important, and extremely long message. " +
                         "We cannot afford to leave any part of it out, " + 
                         "nor do we want line-breaks in the output. " +
                         "Using string concatenation lets us use short lines here, " +
                         "and still get a long line in the output")

Blank Lines and Whitespace

Surround function and class definitions with two blank lines.

Method definitions within a class are surrounded by a single blank line.

Blank lines may be omitted between a bunch of related one-liners (e.g. empty functions)

Additional blank lines may be used sparingly to separate groups of related functions, or within functions to indicate logical sections (e.g. before a block comment).

End each file with a single blank line.

Trailing spaces

Lines should not have trailing whitespace. Extra spaces result in future edits where the only change is a space being added or removed, making the analysis of the changes more difficult for no reason.

Spaces around parameters and operators

You should use a single space around parameter names and operators, including comparison operators and math and assignment operators, even when the spaces are not necessary for PowerShell to correctly parse the code.

One notable exception is when using colons to pass values to switch parameters:

# Do not write:
$variable=Get-Content $FilePath -Wai:($ReadCount-gt0) -First($ReadCount*5)

# Instead write:
$variable = Get-Content -Path $FilePath -Wait:($ReadCount -gt 0) -TotalCount ($ReadCount * 5)

Another exception is when using Unary Operators:

# Do not write:
$yesterdaysDate = (Get-Date).AddDays( - 1)

$i = 0
$i ++

# Instead write:
$yesterdaysDate = (Get-Date).AddDays(-1)

$i = 0
$i++

# Same principle should be applied when using a variable.
$yesterdaysDate = (Get-Date).AddDays(-$i)

Spaces around special characters

White-space is (mostly) irrelevant to PowerShell, but its proper use is key to writing easily readable code.

Use a single space after commas and semicolons, and around pairs of curly braces.

Subexpressions $( ... ) and scriptblocks { ... } should have a single space on the inside of the braces or parentheses to improve readability by making code blocks stand out -- and to further distinguish scriptblocks from variable delimiter braces ${...}

Avoid unnecessary spaces inside parenthesis or square braces.

$Var = 1
"This is a string with one (${Var}) delimited variable."

"There are $( (Get-ChildItem).Count ) files."

Obviously, these rules should not be applied in such a way as to affect output.

Avoid Using Semicolons (;) as Line Terminators

PowerShell will not complain about extra semicolons, but they are unnecessary, and can get in the way when code is being edited or copy-pasted. They also result in extra do-nothing edits in source control when someone finally decides to delete them.

They are also unnecessary when declaring hashtables if you are already putting each element on its own line:

# This is the preferred way to declare a hashtable if it extends past one line:
$Options = @{
    Margin   = 2
    Padding  = 2
    FontSize = 24
}

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