How can I make PowerShell handle [ or ] in file name well?

Question

I modified PowerShell script from PowerShell - Batch change files encoding To UTF-8.

# Modified version of https://stackoverflow.com/q/18684793

[Threading.Thread]::CurrentThread.CurrentUICulture = 'en-US'

$Encoding = New-Object System.Text.UTF8Encoding($True) # If UTF8Encoding($False), It will be UTF-8 without BOM
$source = "C:\Users\AKULA\Desktop\SRC" # source directory
$destination = "C:\Users\AKULA\Desktop\DST" # destination directory

if (!(Test-Path $destination)) {
    New-Item -Path $destination -ItemType Directory | Out-Null
}

# Delete all previously generated file
Get-ChildItem -Path $destination -Include * -File -Recurse | ForEach-Object {$_.Delete()}

# Recursively convert all files into UTF-8
foreach ($i in Get-ChildItem $source -Force -Recurse -Exclude "desktop.ini") {
    if ($i.PSIsContainer) {
        continue
    }

    $name = $i.Fullname.Replace($source, $destination)

    $content = Get-Content $i.Fullname

    if ($null -ne $content) {
        [System.IO.File]::WriteAllLines($name, $content, $Encoding)
    } else {
        Write-Host "No content from: $i"   
    }
}

But after using it, I've found that PS cannot handle [ or ] well. I made some test files that has diversity in name/content.

Get-Content : An object at the specified path C:\Users\AKULA\Desktop\SRC\FILENAME[[[[[[]]]]]]]].txt does not exist, or
has been filtered by the -Include or -Exclude parameter.
At C:\Users\AKULA\Desktop\Convert_to_UTF-8.ps1:24 char:16
+     $content = Get-Content $i.Fullname
+                ~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (System.String[]:String[]) [Get-Content], Exception
    + FullyQualifiedErrorId : ItemNotFound,Microsoft.PowerShell.Commands.GetContentCommand

Since I cannot embed images in question, here is link of IMGUR album.
Full image list: https://i.stack.imgur.com/LtSBS.jpg

These are what I've tested:

• Test files have different names. Their name contains space, ', []. Also made up different language(Japanese, Korean).
• These files have same content, encoded with UCS-2 BE BOM(UTF-16 BE) so that I can check if it has re-encoded to UTF-8.

How can I make my script handle [ or ] in file name well?

Answer 1

tl;dr

Indeed, use of the -LiteralPath parameter is the best solution (in PowerShell (Core) v6+, you can shorten to -lp):

$content = Get-Content -LiteralPath $i.Fullname

-LiteralPath ensures that $i.Fullname is taken verbatim (literally); that is, [ and ] in the path are interpreted as themselves rather than having special meaning, as they would have as a -Path argument, due to being interpreted as a wildcard expression - note that -Path is positionally implied if you only pass a value (a string) as the first argument, as you did (Get-Content $i.FullName)

Note: This answer analogously applies to all cmdlets that have both -Path and
-LiteralPath parameters, such as Set-Content, Out-File, and Set-Location.

---

As for what you tried:

$content = Get-Content $i.Fullname

is effectively the same as:

$content = Get-Content -Path $i.Fullname

That is, the (first) positional argument passed to Get-Content is implicitly bound to the
-Path parameter.

The -Path parameter accepts wildcard expressions to allow matching paths by patterns; in addition to support for * (any run of characters) and ? (exactly 1 character), [...] inside a wildcard pattern denotes a character set or range (e.g., [12] or [0-9]).

Therefore an actual path that contains [...], e.g., foo[10].txt, is not recognized as such, because the [10] is interpreted as a character set matching a single character that is either 1 or 0; that is foo[10].txt would match foo0.txt and foo1.txt, but not a file literally named foo[10].txt.

When (implicitly) using -Path, it is possible to escape [ and ] instances that should be interpreted verbatim, namely via the backtick (`), but note that this can get tricky to get right when quoting and/or variable references are involved.

If you know a path to be a literal path, it is best to form a habit of using -LiteralPath (which in PowerShell Core you can shorten to -lp).

However, if your path contains literal [ and ] and you also need wildcard matching, you must use `-escaping - see this answer.

Answer 2

There are at least two situations where the solution's good advice doesn't hold, unfortunately.

Selective error handling (PS: only an issue in legacy Windows PowerShell)

Get-Content -LiteralPath "nobox[]" gives an error message and exception type as if wildcards are involved:

Get-Content : An object at the specified path box[] does not exist, or has been filtered by the -Include or -Exclude parameter.
At line:1 char:1
+ Get-Content -Path "nobox[]"
+ ~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (System.String[]:String[]) [Get-Content], Exception
    + FullyQualifiedErrorId : ItemNotFound,Microsoft.PowerShell.Commands.GetContentCommand

whereas without the brackets, we get:

Get-Content : Cannot find path 'nobox' because it does not exist.
At line:1 char:1
+ Get-Content -LiteralPath "nobox"
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (nobox:String) [Get-Content], ItemNotFoundException
    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetContentCommand

Therefore, to silently deal with an optional file, but not bluntly suppress every exception, something like:

   try {
        $lines = Get-Content -LiteralPath $path -ErrorAction Stop
    }
    catch [System.Management.Automation.ItemNotFoundException] {
        $lines = @()
    }

chokes on paths with brackets.

Creating a hard or symbolic link

A minor and a major caveat:

• The Path parameter, the name of the new item, "works like the LiteralPath parameter of other cmdlets", says the documentation of New-Item clearly, and that seems true and makes sense. Though I wish we could clarify that by writing -LiteralPath.
• The Value parameter, the target of the link (also known as Target secretly in v5 and openly later), does not accept wildcard characters according to the same documentation, but that's a lie. The command:

New-Item -ItemType "HardLink" -Path "whatever" -Target "*"

makes Powershell squeal "Cannot set the location because path '*' resolved to multiple containers.".

So you always need the escapes for the target. If you have a file named "f[]", then this will display an error:

New-Item -ItemType "HardLink" -Path "whatever" -Target "f[]"

and this will create a link:

New-Item -ItemType "HardLink" -Path "f[2]" -Target ([WildcardPattern]::Escape("f[]"))

Same for ItemType "SymbolicLink".