[SOLVED] How to generate and apply git patches correctly in Powershell (vs bash)?

Issue

Please, observe the following short scenario (this is in Powershell):

PS> git diff -U3 -r -M HEAD -- .\Metadata\LegacyTypeModules\xyz.Web.Main.draft.json | Out-File -Encoding ascii c:\temp\1.diff

PS> git apply --cached C:\temp\1.diff
error: patch failed: Metadata/LegacyTypeModules/xyz.Web.Main.draft.json:69
error: Metadata/LegacyTypeModules/xyz.Web.Main.draft.json: patch does not apply

This fails because the last line in the file does not end with CRLF:

However, the same exact commands work when run in bash:

$ git diff -U3 -r -M HEAD -- Metadata/LegacyTypeModules/xyz.Web.Main.draft.json > /c/Temp/2.diff

$ git apply --cached /c/Temp/2.diff

P11F70F@L-R910LPKW MINGW64 /c/xyz/tip (arch/1064933)

The difference between the two patches is:

So the problem seems to happen because Powershell terminates each line going through the pipe with CRLF whereas bash preserves the original line endings.

I understand why this happens - Powershell operates with objects and the objects are strings excluding the EOL characters. When writing to file Powershell converts objects to strings (in the case of strings the conversion is a nop) and uses the default EOL sequence to delimit the lines.

Does it mean Powershell cannot be used at all in EOL sensitive scenarios?

Solution

Indeed:

• PowerShell, up to v7.3.x, invariably decodes output from external programs as text (using [Console]::OutputEncoding).

• It then sends the decoded output line by line through the pipeline, as lines become available.

• A file-output cmdlet such as Out-File then invariably uses the platform-native newline sequence - CRLF on Windows - to terminate each (stringified) input object when writing to the target file (using its default character encoding (or the one specified via -Encoding), which is technically unrelated to the encoding that was used to decode the external-program output).

In other words:

• In Windows PowerShell and PowerShell (Core) up to v7.3.x, PowerShell pipelines (and redirections) do not support passing raw binary data through.

• They do, however, in PowerShell (Core) v7.4+ (see this answer).

  • Note that you'll have to use > rather than Out-File in order to capture the raw byte output from an external program such as git, just like in Bash.
  • In other words: in v7.4+, your Bash command can be used as-is in PowerShell.

Workarounds for v7.3-:

• Manually join and terminate the decoded output lines with LF newlines ("`n"), and write the resulting multi-line string as-is (-NoNewLine) to the target file, as shown in zdan's helpful answer.

• In this simple case it is easiest to delegate to cmd.exe /c, given that cmd.exe's pipelines and redirections are raw byte conduits:

cmd /c @'
git diff -U3 -r -M HEAD -- .\Metadata\LegacyTypeModules\xyz.Web.Main.draft.json > c:\temp\1.diff
'@

^{Note the use of a here-string for readability and ease of any embedded quoting (n/a here).}

Answered By - mklement0

Answer Checked By - Senaida (WPSolving Volunteer)