PowerShell get number of lines of big (large) file

One of the ways to get number of lines from a file is this method in PowerShell:

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>

However, when I have a large 800 MB text file, how do I get the line number from it without reading the whole file?

The above method will consume too much RAM resulting in crashing the script or taking too long to complete.

Use Get-Content -Read $nLinesAtTime to read your file part by part:

$nlines = 0;

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

And here is simple, but slow script to validate work on a small file:

gc $YOURFILE | Measure-Object -Line

Here's a PowerShell script I cobbled together which demonstrates a few different methods of counting lines in a text file, along with the time and memory required for each method. The results (below) show clear differences in the time and memory requirements. For my tests, it looks like the sweet spot was Get-Content, using a ReadCount setting of 100. The other tests required significantly more time and/or memory usage.

#$testFile = 'C:\test_small.csv' # 245 lines, 150 KB
#$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

Here are results for text file containing ~95k lines, 104 MB:

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

Here are results for a larger file (containing ~285k lines, 308 MB):

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

PowerShell get number of lines of big (large) file

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