Add-Content and Out-File are not for performance

Linchi Shea — Mon, 04 Jan 2010 21:31:00 GMT

When you write Powershell scripts and need to write a text file, you have a number of ways to accomplish that. The often suggested approach is to use cmdlets Add-Content or Out-File. Well, this is not news.

But some may not notice that these cmdlets are not there for performance. Sure, they are convenient. But if you need to write to a file many times, you may want to consider something else. To demonstrate the point, try the following script, which tests the performance of writing to a text file 10,000 times:

# Measure Add-Content

$t = get-date;

for ($a=1; $a -le 10000; $a++)

{

add-content -path "c:\junk\test1.txt" -value "Hello";

}

$s = $(get-date).subtract($t).TotalMilliseconds;

write-output ("Add-Content: " + $s);

# Measure Out-File

$t = get-date;

for ($a=1; $a -le 10000; $a++)

{

"Hello" | out-file -filepath "c:\junk\test2.txt" -append

}

$s = $(get-date).subtract($t).TotalMilliseconds;

write-output ("Out-File: " + $s);

# Measure StreamWriter

$t = get-date;

$sw = New-Object System.IO.StreamWriter "c:\junk\test3.txt";

for ($a=1; $a -le 10000; $a++)

{

$sw.WriteLine("Hello")

}

$sw.Close();

$s = $(get-date).subtract($t).TotalMilliseconds;

write-output ("StreamWriter: " + $s);

The output from this script is similar to what I obtained from my laptop and shown below:

Add-Content: 34015.8427

Out-File: 37781.4918

StreamWriter: 781.255

From running this scripts multiple times on my laptop, using StreamWriter was consistently about 4 ~ 5 times faster than either Add-Content or Out-File. This should not really be surprising because each time you call Add-Content or Out-File, you open and close the file, and that is expensive.

Performance wise, using Add-Content or Out-File is similar to using StreamWriter in the following way (i.e. including opening and closing the file inside the loop):

# Measure StreamWriter, open/close the file for every write

$t = get-date;

for ($a=1; $a -le 10000; $a++)

{

$sw = New-Object -typename System.IO.StreamWriter("c:\junk\test4.txt", "true");

$sw.WriteLine("Hello")

$sw.Close();

}

$s = $(get-date).subtract($t).TotalMilliseconds;

write-output ("StreamWriter2:" + $s);

And if you run the above script, you should find its performance very similar to that of Add-Content or that of Out-File.

So what is the takeaway? Well, do not use Add-Content or Out-File if performance matters such as when you write a massive number of lines to a file.

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Add-Content and Out-File are not for performance