如何使用PowerShell打印文件的某一行？

Question

我在这台服务器上没有一个像样的文本编辑器,但是我需要看看是什么导致某个文件的第10行出错.我确实有PowerShell ......

Answer 1

它就像使用select一样简单:

Get-Content file.txt | Select -Index (line - 1)

例如,获得第5行

Get-Content file.txt | Select -Index 4

或者您可以使用:

(Get-Content file.txt)[4]

Answer 2

这将显示myfile.txt的第10行:

get-content myfile.txt | select -first 1 -skip 9

两个-first和-skip是可选参数,并且-context,或者-last可以是在类似情况下是有用的.

Answer 3

您可以使用cmdlet的-TotalCount参数来读取第一行,然后使用仅返回第n行:Get-ContentnSelect-Objectn

Get-Content file.txt -TotalCount 9 | Select-Object -Last 1;

根据@CB的评论,这应该通过只读取包括第一n行而不是整个文件来提高性能.请注意,您可以使用别名-First或-Head代替-TotalCount.

Answer 4

只是为了好玩，这里有一些测试：

# Added this for @Graimer's request ;) (not same computer, but one with HD little more
# performant...)
> measure-command { Get-Content ita\ita.txt -TotalCount 260000 | Select-Object -Last 1 }


Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 28
Milliseconds      : 893
Ticks             : 288932649
TotalDays         : 0,000334412788194444
TotalHours        : 0,00802590691666667
TotalMinutes      : 0,481554415
TotalSeconds      : 28,8932649
TotalMilliseconds : 28893,2649


> measure-command { (gc "c:\ps\ita\ita.txt")[260000] }


Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 9
Milliseconds      : 257
Ticks             : 92572893
TotalDays         : 0,000107144552083333
TotalHours        : 0,00257146925
TotalMinutes      : 0,154288155
TotalSeconds      : 9,2572893
TotalMilliseconds : 9257,2893


> measure-command { ([System.IO.File]::ReadAllLines("c:\ps\ita\ita.txt"))[260000] }


Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 0
Milliseconds      : 234
Ticks             : 2348059
TotalDays         : 2,71766087962963E-06
TotalHours        : 6,52238611111111E-05
TotalMinutes      : 0,00391343166666667
TotalSeconds      : 0,2348059
TotalMilliseconds : 234,8059



> measure-command {get-content .\ita\ita.txt | select -index 260000}


Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 36
Milliseconds      : 591
Ticks             : 365912596
TotalDays         : 0,000423509949074074
TotalHours        : 0,0101642387777778
TotalMinutes      : 0,609854326666667
TotalSeconds      : 36,5912596
TotalMilliseconds : 36591,2596

获胜者是： ([System.IO.File]::ReadAllLines( path ))[index]

Answer 5

这是一个System.IO直接使用.NET 类的函数：

function GetLineAt([String] $path, [Int32] $index)
{
    [System.IO.FileMode] $mode = [System.IO.FileMode]::Open;
    [System.IO.FileAccess] $access = [System.IO.FileAccess]::Read;
    [System.IO.FileShare] $share = [System.IO.FileShare]::Read;
    [Int32] $bufferSize = 16 * 1024;
    [System.IO.FileOptions] $options = [System.IO.FileOptions]::SequentialScan;
    [System.Text.Encoding] $defaultEncoding = [System.Text.Encoding]::UTF8;
    # FileStream(String, FileMode, FileAccess, FileShare, Int32, FileOptions) constructor
    # http://msdn.microsoft.com/library/d0y914c5.aspx
    [System.IO.FileStream] $input = New-Object `
        -TypeName 'System.IO.FileStream' `
        -ArgumentList ($path, $mode, $access, $share, $bufferSize, $options);
    # StreamReader(Stream, Encoding, Boolean, Int32) constructor
    # http://msdn.microsoft.com/library/ms143458.aspx
    [System.IO.StreamReader] $reader = New-Object `
        -TypeName 'System.IO.StreamReader' `
        -ArgumentList ($input, $defaultEncoding, $true, $bufferSize);
    [String] $line = $null;
    [Int32] $currentIndex = 0;

    try
    {
        while (($line = $reader.ReadLine()) -ne $null)
        {
            if ($currentIndex++ -eq $index)
            {
                return $line;
            }
        }
    }
    finally
    {
        # Close $reader and $input
        $reader.Close();
    }

    # There are less than ($index + 1) lines in the file
    return $null;
}

GetLineAt 'file.txt' 9;

调整$bufferSize变量可能会影响性能。使用默认缓冲区大小并且不提供优化提示的更简洁的版本可能如下所示：

function GetLineAt([String] $path, [Int32] $index)
{
    # StreamReader(String, Boolean) constructor
    # http://msdn.microsoft.com/library/9y86s1a9.aspx
    [System.IO.StreamReader] $reader = New-Object `
        -TypeName 'System.IO.StreamReader' `
        -ArgumentList ($path, $true);
    [String] $line = $null;
    [Int32] $currentIndex = 0;

    try
    {
        while (($line = $reader.ReadLine()) -ne $null)
        {
            if ($currentIndex++ -eq $index)
            {
                return $line;
            }
        }
    }
    finally
    {
        $reader.Close();
    }

    # There are less than ($index + 1) lines in the file
    return $null;
}

GetLineAt 'file.txt' 9;