Memory errors merging multiple large csv files with Powershell

It's simply nuts the way that some people do this using this approach...

Get-Content $SrcFile1, $SrcFile2 | Set-Content $DstFile

Dont do it that way! It's ridiculously slow and invariably leads to memory exception errors. Instead use the good old file copy from the command processor e.g...

cmd /c "copy $($SrcFile1) + $($SrcFile2) $($DstFile)"

I don't have a large file to test this with, but using .net methods might be an alternative as you can just work on 1 row at a time rather than loading the whole thing in to memory.

$filepath = "c:\temp"
$outputfile = "c:\temp\output\result.csv"
$encoding = [System.Text.Encoding]::UTF8

$files = Get-ChildItem -Path $filePath -Filter *.csv

$w = New-Object System.IO.StreamWriter($outputfile, $true, $encoding)

$skiprow = $false
foreach ($file in $files)
{
    $r = New-Object System.IO.StreamReader($file.fullname, $encoding)
    while (($line = $r.ReadLine()) -ne $null) 
    {
        if (!$skiprow)
        {
            $w.WriteLine($line)
        }
        $skiprow = $false
    }
    $r.Close()
    $r.Dispose()
    $skiprow = $true
}

$w.close()
$w.Dispose()

A complete answer evolved from the great point Bob made

<###########################
user config section
###########################>

# location of files to concatenate
$sourcefolder = "P:\DWH\ntm_v1\uncompressed"

# source file extension
$ext = "*.csv"

# output folder (best to have new folder for safety)
$outfolder = $sourcefolder + "\..\concatenated"

#output file name
$outfilename = "concat.txt"

<###########################
do work
###########################>

# build full path to out file
$concatfile = $outfolder + "\" + $outfilename

#create output folder
md -Force $outfolder

# delete output file if exists
if (Test-Path $concatfile) 
{
  Remove-Item -Confirm $concatfile
}

ForEach ($file in (Get-ChildItem -Path $sourcefolder -Filter $ext)) {
    $param = "type $file >> $concatfile"
    Write-Host "cmd /c $param"
        
    # run concat command
    cmd /c $param;  
}