Powershell – Read UTF-8 files correctly with PowerShell

encodingpowershellutf-8

Following situation:

A PowerShell script creates a file with UTF-8 encoding
The user may or may not edit the file, possibly losing the BOM, but should keep the encoding as UTF-8, and possibly changing the line separators
The same PowerShell script reads the file, adds some more content and writes it all as UTF-8 back to the same file
This can be iterated many times

With Get-Content and Out-File -Encoding UTF8 I have problems reading it correctly. It's stumbling over the BOM it has written before (putting it in the content, breaking my parsing regex), does not use UTF-8 encoding and even deletes line breaks in the original content part.

I need a function that can read any file with UTF-8 encoding, ignore and delete the BOM and not modify the content. What should I use?

Update

I have added a little test script that shows what I'm trying to do and what happens instead.

# Read data if exists
$data = ""
$startRev = 1;
if (Test-Path test.txt)
{
    $data = Get-Content -Path test.txt
    if ($data -match "^[0-9-]{10} - r([0-9]+)")
    {
        $startRev = [int]$matches[1] + 1
    }
}
Write-Host Next revision is $startRev

# Define example data to add
$startRev = $startRev + 10
$newMsgs = "2014-04-01 - r" + $startRev + "`r`n`r`n" + `
    "Line 1`r`n" + `
    "Line 2`r`n`r`n"

# Write new data back
$data = $newMsgs + $data
$data | Out-File test.txt -Encoding UTF8

After running it a few times, new sections should be added to the beginning of the file, the existing content should not be altered in any way (currently loses line breaks) and no additional new lines should be added at the end of the file (seems to happen sometimes).

Instead, the second run gives me an error.

Best Answer

If the file is supposed to be UTF8 why don't you try to read it decoding UTF8 :

Get-Content -Path test.txt -Encoding UTF8

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Stand-alone utility approach

iconv -f ISO-8859-1 -t UTF-8 in.txt > out.txt

-f ENCODING  the encoding of the input
-t ENCODING  the encoding of the output

You don't have to specify either of these arguments. They will default to your current locale, which is usually UTF-8.

Php – UTF-8 all the way through

Data Storage:

Specify the utf8mb4 character set on all tables and text columns in your database. This makes MySQL physically store and retrieve values encoded natively in UTF-8. Note that MySQL will implicitly use utf8mb4 encoding if a utf8mb4_* collation is specified (without any explicit character set).
In older versions of MySQL (< 5.5.3), you'll unfortunately be forced to use simply utf8, which only supports a subset of Unicode characters. I wish I were kidding.

Data Access:

In your application code (e.g. PHP), in whatever DB access method you use, you'll need to set the connection charset to utf8mb4. This way, MySQL does no conversion from its native UTF-8 when it hands data off to your application and vice versa.
Some drivers provide their own mechanism for configuring the connection character set, which both updates its own internal state and informs MySQL of the encoding to be used on the connection—this is usually the preferred approach. In PHP:
- If you're using the PDO abstraction layer with PHP ≥ 5.3.6, you can specify charset in the DSN:
```
 $dbh = new PDO('mysql:charset=utf8mb4');
```
- If you're using mysqli, you can call set_charset():
```
  $mysqli->set_charset('utf8mb4');       // object oriented style
  mysqli_set_charset($link, 'utf8mb4');  // procedural style
```
- If you're stuck with plain mysql but happen to be running PHP ≥ 5.2.3, you can call mysql_set_charset.
If the driver does not provide its own mechanism for setting the connection character set, you may have to issue a query to tell MySQL how your application expects data on the connection to be encoded: SET NAMES 'utf8mb4'.
The same consideration regarding utf8mb4/utf8 applies as above.

Output:

If your application transmits text to other systems, they will also need to be informed of the character encoding. With web applications, the browser must be informed of the encoding in which data is sent (through HTTP response headers or HTML metadata).
In PHP, you can use the default_charset php.ini option, or manually issue the Content-Type MIME header yourself, which is just more work but has the same effect.
When encoding the output using json_encode(), add JSON_UNESCAPED_UNICODE as a second parameter.

Input:

Unfortunately, you should verify every received string as being valid UTF-8 before you try to store it or use it anywhere. PHP's mb_check_encoding() does the trick, but you have to use it religiously. There's really no way around this, as malicious clients can submit data in whatever encoding they want, and I haven't found a trick to get PHP to do this for you reliably.
From my reading of the current HTML spec, the following sub-bullets are not necessary or even valid anymore for modern HTML. My understanding is that browsers will work with and submit data in the character set specified for the document. However, if you're targeting older versions of HTML (XHTML, HTML4, etc.), these points may still be useful:
- For HTML before HTML5 only: you want all data sent to you by browsers to be in UTF-8. Unfortunately, if you go by the only way to reliably do this is add the accept-charset attribute to all your <form> tags: <form ... accept-charset="UTF-8">.
- For HTML before HTML5 only: note that the W3C HTML spec says that clients "should" default to sending forms back to the server in whatever charset the server served, but this is apparently only a recommendation, hence the need for being explicit on every single <form> tag.

Other Code Considerations:

Obviously enough, all files you'll be serving (PHP, HTML, JavaScript, etc.) should be encoded in valid UTF-8.
You need to make sure that every time you process a UTF-8 string, you do so safely. This is, unfortunately, the hard part. You'll probably want to make extensive use of PHP's mbstring extension.
PHP's built-in string operations are not by default UTF-8 safe. There are some things you can safely do with normal PHP string operations (like concatenation), but for most things you should use the equivalent mbstring function.
To know what you're doing (read: not mess it up), you really need to know UTF-8 and how it works on the lowest possible level. Check out any of the links from utf8.com for some good resources to learn everything you need to know.

Best Answer

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Php – UTF-8 all the way through

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