Powershell Count lines extremely large file

If performance matters, avoid the use of cmdlets and the pipeline; use switch -File:

$count = 0
switch -File C:\test.txt { default { ++$count } }

switch -File enumerates the lines of the specified file; condition default matches any line.

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To give a sense of the performance difference:

# Create a sample file with 100,000 lines.
1..1e5 > tmp.txt
# Warm up the file cache
foreach ($line in [IO.File]::ReadLines("$pwd/tmp.txt")) { }

(Measure-Command { (Get-Content tmp.txt | Measure-Object).Count }).TotalSeconds

(Measure-Command { $count = 0; switch -File tmp.txt { default { ++$count } } }).TotalSeconds

Sample results from my Windows 10 / PSv5.1 machine:

1.3081307  # Get-Content + Measure-Object
0.1097513  # switch -File

That is, on my machine the switch -File command was about 12 times faster.

For such a huge file I'd rather go with some C written utility. Install gitbash, it should have wc command:

wc -l yourfile.txt

I tested it on 5GB/50M line file (on HDD), it took about 40s. The best powershell solution took about 2 minutes. You also may check your file, it might have some auto incremental indexes or constant row size.