Git clone: Redirect stderr to stdout but keep errors being written to stderr

Question

git clone writes its output to stderr as documented here. I can redirect this with the following command:

git clone https://myrepo          


        

Answer 1

Generally speaking:

• Console (terminal) applications - whether on Windows or on Unix-like platforms - only have two output streams at their disposal:

  • stdout (standard output) - this is where data ("return values") goes.
  • stderr (standard error) - this is where error messages and - for lack of additional streams - anythings else that isn't data goes, such as progress and status information.

• Therefore, you cannot and shouldn't infer success vs. failure from the presence of stderr output.

  • Instead, you must rely solely on an application's process exit code:

    • 0 indicates success
    • any nonzero value indicates failure

  • In PowerShell, the **process exit code is reflected in automatic variable $LASTEXITCODE**.

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Specifically, this means:

• Given git's stderr output lines, you cannot infer whether they represent error message or other kind of non-data information, such as progress or status messages, which git frequently uses.

  • Telling git to categorically redirect its stderr output to stdout (by setting environment variable GIT_REDIRECT_STDERR to string 2>&1; $env:GIT_REDIRECT_STDERR = '2>&1' in PowerShell) does not help, because error messages and progress/status messages alike are then sent there.

• As stated, you should only infer failure from a nonzero exit code.

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A pragmatic approach is to do the following:

# Invoke git and capture both its stdout and stderr streams.
$result = git clone https://myrepo c:\repo 2>&1
# Throw an error, if git indicated failure.
if ($LASTEXITCODE) { Throw "git failed (exit code: $LASTEXITCODE):`n$($result -join "`n")" }                                            #`
# Output the captured result, as an array of strings
$result | % ToString 

Note:

• | % ToString ensures that only strings are output, given that the stderr lines (via stream 2) redirected to (>) the success output stream (&1) are wrapped in System.Management.Automation.ErrorRecord instances.

• 2>&1 can have unexpected side effects - see this answer for background information.

• Better integration of external-program calls into PowerShell's error handling is the subject of this RFC draft, notably to have the option to abort execution automatically on encountering a nonzero exit code.