PowerShell获取大(大)文件的行数

Question

从文件中获取行数的方法之一是PowerShell中的以下方法：

PS C:\Users\Pranav\Desktop\PS_Test_Scripts> $a=Get-Content .\sub.ps1
PS C:\Users\Pranav\Desktop\PS_Test_Scripts> $a.count
34
PS C:\Users\Pranav\Desktop\PS_Test_Scripts> 

但是，当我有一个很大的800MB文本文件时，如何在不读取整个文件的情况下获得行号？

上面的方法会消耗太多的RAM，导致脚本崩溃或需要太长时间才能完成。

Answer 1

使用Get-Content -Read $nLinesAtTime逐部分读取文件：

$nlines = 0;

# Read file by 1000 lines at a time
gc $YOURFILE -read 1000 | % { $nlines += $_.Length };
[string]::Format("{0} has {1} lines", $YOURFILE, $nlines)

下面是一个简单但很慢的脚本，用来验证一个小文件上的工作：

gc $YOURFILE | Measure-Object -Line

Answer 2

下面是我拼凑起来的一个PowerShell脚本，它演示了在文本文件中计算行数的几种不同方法，以及每种方法所需的时间和内存。结果(如下)显示了时间和内存需求的明显差异。在我的测试中，Get-Content似乎是最好的选择，使用的ReadCount设置为100。其他测试需要更多的时间和/或内存使用。

#$testFile = 'C:\test_small.csv' # 245 lines, 150 KB
#$testFile = 'C:\test_medium.csv' # 95,365 lines, 104 MB
$testFile = 'C:\test_large.csv' # 285,776 lines, 308 MB

# Using ArrayList just because they are faster than Powershell arrays, for some operations with large arrays.
$results = New-Object System.Collections.ArrayList

function AddResult {
param( [string] $sMethod, [string] $iCount )
    $result = New-Object -TypeName PSObject -Property @{
        "Method" = $sMethod
        "Count" = $iCount
        "Elapsed Time" = ((Get-Date) - $dtStart)
        "Memory Total" = [System.Math]::Round((GetMemoryUsage)/1mb, 1)
        "Memory Delta" = [System.Math]::Round(((GetMemoryUsage) - $dMemStart)/1mb, 1)
    }
    [void]$results.Add($result)
    Write-Output "$sMethod : $count"
    [System.GC]::Collect()
}

function GetMemoryUsage {
    # return ((Get-Process -Id $pid).PrivateMemorySize)
    return ([System.GC]::GetTotalMemory($false))
}

# Get-Content -ReadCount 1
[System.GC]::Collect()
$dMemStart = GetMemoryUsage
$dtStart = Get-Date
$count = 0
Get-Content -Path $testFile -ReadCount 1 |% { $count++ }
AddResult "Get-Content -ReadCount 1" $count

# Get-Content -ReadCount 10,100,1000,0
# Note: ReadCount = 1 returns a string.  Any other value returns an array of strings.
# Thus, the Count property only applies when ReadCount is not 1.
@(10,100,1000,0) |% {
    $dMemStart = GetMemoryUsage
    $dtStart = Get-Date
    $count = 0
    Get-Content -Path $testFile -ReadCount $_ |% { $count += $_.Count }
    AddResult "Get-Content -ReadCount $_" $count
}

# Get-Content | Measure-Object
$dMemStart = GetMemoryUsage
$dtStart = Get-Date
$count = (Get-Content -Path $testFile -ReadCount 1 | Measure-Object -line).Lines
AddResult "Get-Content -ReadCount 1 | Measure-Object" $count

# Get-Content.Count
$dMemStart = GetMemoryUsage
$dtStart = Get-Date
$count = (Get-Content -Path $testFile -ReadCount 1).Count
AddResult "Get-Content.Count" $count

# StreamReader.ReadLine
$dMemStart = GetMemoryUsage
$dtStart = Get-Date
$count = 0
# Use this constructor to avoid file access errors, like Get-Content does.
$stream = New-Object -TypeName System.IO.FileStream(
    $testFile,
    [System.IO.FileMode]::Open,
    [System.IO.FileAccess]::Read,
    [System.IO.FileShare]::ReadWrite)
if ($stream) {
    $reader = New-Object IO.StreamReader $stream
    if ($reader) {
        while(-not ($reader.EndOfStream)) { [void]$reader.ReadLine(); $count++ }
        $reader.Close()
    }
    $stream.Close()
}

AddResult "StreamReader.ReadLine" $count

$results | Select Method, Count, "Elapsed Time", "Memory Total", "Memory Delta" | ft -auto | Write-Output

以下是包含约95k行、104MB的文本文件的结果：

Method                                    Count Elapsed Time     Memory Total Memory Delta
------                                    ----- ------------     ------------ ------------
Get-Content -ReadCount 1                  95365 00:00:11.1451841         45.8          0.2
Get-Content -ReadCount 10                 95365 00:00:02.9015023         47.3          1.7
Get-Content -ReadCount 100                95365 00:00:01.4522507         59.9         14.3
Get-Content -ReadCount 1000               95365 00:00:01.1539634         75.4         29.7
Get-Content -ReadCount 0                  95365 00:00:01.3888746          346        300.4
Get-Content -ReadCount 1 | Measure-Object 95365 00:00:08.6867159         46.2          0.6
Get-Content.Count                         95365 00:00:03.0574433        465.8        420.1
StreamReader.ReadLine                     95365 00:00:02.5740262         46.2          0.6

以下是一个较大文件(包含约285k行，308 MB)的结果：

Method                                    Count  Elapsed Time     Memory Total Memory Delta
------                                    -----  ------------     ------------ ------------
Get-Content -ReadCount 1                  285776 00:00:36.2280995         46.3          0.8
Get-Content -ReadCount 10                 285776 00:00:06.3486006         46.3          0.7
Get-Content -ReadCount 100                285776 00:00:03.1590055         55.1          9.5
Get-Content -ReadCount 1000               285776 00:00:02.8381262         88.1         42.4
Get-Content -ReadCount 0                  285776 00:00:29.4240734        894.5        848.8
Get-Content -ReadCount 1 | Measure-Object 285776 00:00:32.7905971         46.5          0.9
Get-Content.Count                         285776 00:00:28.4504388       1219.8       1174.2
StreamReader.ReadLine                     285776 00:00:20.4495721           46          0.4

Answer 3

这是基于Pseudothink的帖子的一行代码。

一个特定文件中的行：

"the_name_of_your_file.txt" |% {$n = $_; $c = 0; Get-Content -Path $_ -ReadCount 1000 |% { $c += $_.Count }; "$n; $c"}

当前目录中的所有文件(单独)：

Get-ChildItem "." |% {$n = $_; $c = 0; Get-Content -Path $_ -ReadCount 1000 |% { $c += $_.Count }; "$n; $c"}

说明：

"the_name_of_your_file.txt" ->什么也不做，只提供下一步的文件名，需要用双引号引起来

|% ->别名ForEach-Object，遍历提供的项(在本例中只有一个)，接受管道内容作为输入，当前项保存到$_

$n = $_ -> $n提供的文件名是从$_保存的，实际上可能不需要这样做

$c as计数的$c = 0 ->初始化

Get-Content -Path $_ -ReadCount 1000 ->从提供的文件中读取1000行(请参阅该线程的其他答案)

|% -> foreach确实添加了实际读取到$c的行数(将类似于1000 + 1000 + 123)

"$n; $c" ->读取完文件后，打印文件名；行数

Get-ChildItem "." ->只是向管道中添加了比单个文件名多的项目