在 PowerShell 中抑制 Git 命令的输出

Question

As part of a script I am running git clean -fd . It typically outputs a bunch of files that are cleaned up. I would like to suppress this output.

I tried git clean -fd | Out-Null git clean -fd | Out-Null but it did not seem to work. Googling returned no options for git to suppress output, so is there another PowerShell method I can use? Or am I doing something wrong? It may be worth noting that the PowerShell script itself is being executed from within a .bat file.

Answer 1

只需添加选项-q ：

git clean -fdq

Answer 2

phd's helpful answer offers the best solution for the case at hand.

As for why ... | Out-Null ... | Out-Null wasn't effective:

Out-Null suppresses only stdout output from external programs such as git , but not stderr output.

git , like many CLIs (console / terminal programs), uses the stderr stream not just to report errors , but also for status information - basically, anything that's not data .

To suppress both stdout and stderr output, use *> $null :

git clean -fd *> $null

Note: *> $null suppresses all output streams ; while external programs only have 2 (stdout and stderr), applying *>$null to a PowerShell-native command silences all 6 output streams.

See about_Redirection for more information.

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Optional reading: Selective stream redirection from external programs:

Building on feedback from nmbell :

• >$null (or 1>$null ) can be used to suppress stdout output selectively , which is effectively the same as | Out-Null | Out-Null .

• 2>$null can be used to suppress stderr output selectively .

• *>$null , as discussed above, silences both (all) streams.

Of course, instead of $null for suppressing output, the redirection target may also may be a file (name or path).

Note:

• PowerShell processes output from external programs line by line in its pipeline, and if the output is captured in a variable ( $out = ... ) and comprises 2 or more lines , it is stored as an array ( [object[]] ) of lines (strings).

• PowerShell only ever "speaks text" (uses strings) with external programs, both when sending and receiving data, which means that character-encoding issues may come into play.

• See this answer for more information on both these aspects.

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Scenarios with examples :

Setup:

# Construct a platform-appropriate command, stored in a script block ({ ... }) 
# that calls an external program (the platform-native shell) that outputs
# 1 line of stdout and 1 line of stderr output each, and can later be 
# invoked with `&`, the call operator.
$externalCmd = if ($env:OS -eq 'Windows_NT') {     # Windows
                 { cmd /c 'echo out & echo err >&2' } 
               } else {                            # Unix (macOS, Linux)
                 { sh -c 'echo out; echo err >&2' } 
               }

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Capture stdout, pass stderr through :

PS> $captured = & $externalCmd; "Captured: $captured"
err            # Stderr output was *passed through*
Captured: out  # Captured stdout output.

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Capture stdout, suppress stderr output, with 2>$null :

PS> $captured = & $externalCmd 2>$null; "Captured: $captured"
Captured: out  # Captured stdout output - stderr output was suppressed.

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Capture both stdout and stderr, with *>&1 :

PS> $captured = & $externalCmd *>&1 | % ToString; "Captured: $captured"
Captured: out err  # *Combined* stdout and stderr output.

Note:

• % ToString is short for ForEach-Object ToString , which calls the .ToString() method on each output object, which ensures that the System.Management.Automation.ErrorRecord instances that PowerShell wraps stderr lines in are converted back to strings .
• $captured receives a 2-element array ( [object[]] ) of lines - containing the stdout and stderr line as elements, respectively; it is PowerShell's string interpolation that turns them into a single-line, space-separated string in this case.

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Capture only stderr , suppress stdout:

PS> $captured = 
      & $externalCmd *>&1 | 
        ? { $_ -is [System.Management.Automation.ErrorRecord] } | 
          % ToString; "Captured: $captured"
Captured: err  # Captured stderr output *only*.

Note:

• ? { $_ -is [System.Management.Automation.ErrorRecord] } ? { $_ -is [System.Management.Automation.ErrorRecord] } is short for
  Where-Object { $_ -is [System.Management.Automation.ErrorRecord] } , which passes only stderr lines - identifiable via the wrapper type being tested for - through, and % ToString again converts them back to strings.

• This technique is neither obvious nor convenient; GitHub suggestion #4332 proposes a syntax such as 2> variable:stderr to support redirecting streams to variables , such as $stderr in this case.