How to get the first line of a really large file in PowerShell? Adam Bertram adviced to use the Select-Object -first 1 instead of (Get-Content -Path "file.txt")[0] # Which is correct, but maybe Switch -file is even faster? test based on https://x.com/adbertram/status/1781642880769032196

FirstLineFast.ps1

# How to get the first line of a really large file in PowerShell?
# Adam Bertram adviced to use the Select-Object -first 1 instead of (Get-Content -Path "file.txt")[0]
# Which is correct, but maybe Switch -file is even faster?
# test based on https://x.com/adbertram/status/1781642880769032196

$longfile = 'HugeFileList.txt' # One million lines - 49MB

# retreive the first line of a file very fast
$firstline = switch -file ($Longfile){Default{$_;break}}

# retreive the first line of a file also fast
$firstline = Get-Content -path $longfile| Select-object -First 1

# Compare the performance of both methods

0..1kb| ForEach-Object{
    [PSCustomObject]@{
        Name = 'Switch'
        Ticks = (measure-command {
            $firstline = switch -file ($Longfile){Default{$_;break}}
        }).Ticks
        
    }
    [PSCustomObject]@{
        Name = 'SelectFirst'
        Ticks = (measure-command {
            $firstline = Get-Content -path $longfile| Select-object -First 1
        
        
        }).Ticks
    }
} | Group-Object -Property Name | ForEach-Object{
    [PSCustomObject]@{
        TestName = $_.Name
        AVGTicks = ($_.Group.Ticks | Measure-Object -Average).Average
    }

} | Sort-Object -Property AVGTicks


<#
    Result for 1024 runs: 

    TestName    AVGTicks
    --------    --------
    Switch       6236.88
    SelectFirst 18622.26
#>

Here is my result:

TestName                  AvgTicks
--------                  --------
Switch            3756,21756097561
StreamReader      14313,5609756098
SelectFirst       21315,0292682927
SelectFirstIOFile 3009278,38536585

And here the test code for it:

0..1kb | ForEach-Object -Process {
   [PSCustomObject]@{
      Name  = 'Switch'
      Ticks = (Measure-Command -Expression {
            $firstline = switch -file ($BigTextFile){Default
               {
                  $_
                  break
               }
            }
      }).Ticks
   }
   [PSCustomObject]@{
      Name  = 'SelectFirst'
      Ticks = (Measure-Command -Expression {
            $firstline = (Get-Content -Path $BigTextFile | Select-Object -First 1)
      }).Ticks
   }
   [PSCustomObject]@{
      Name  = 'SelectFirstIOFile'
      Ticks = (Measure-Command -Expression {
            $firstline = ([io.file]::ReadAllLines($BigTextFile) | Select-Object -First 1)
      }).Ticks
   }
   [PSCustomObject]@{
      Name  = 'StreamReader'
      Ticks = (Measure-Command -Expression {
            try
            {
               $StreamReader = (New-Object -TypeName System.IO.StreamReader -ArgumentList ($BigTextFile))
               $firstline = ($StreamReader.ReadLine() | Select-Object -First 1)
            }
            finally
            {
               $StreamReader.Close()
               $StreamReader = $null
            }
      }).Ticks
   }
} | Group-Object -Property Name | ForEach-Object -Process {
   [PSCustomObject]@{
      TestName = $_.Name
      AvgTicks = ($_.Group.Ticks | Measure-Object -Average).Average
   }
} | Sort-Object -Property AvgTicks