Question

In PowerShell, what’s the difference between Out-File and Set-Content? Or Add-Content and Out-File -append?

I’ve found if I use both against the same file, the text is fully mojibaked.

(A minor second question: > is an alias for Out-File, right?)

Answer 1

Here’s a summary of what I’ve deduced, after a few months experience with PowerShell, and some scientific experimentation. I never found any of this in the documentation 🙁

[Update: Much of this now appears to be better documented.]

Read and write locking

While Out-File is running, another application can read the log file.

While Set-Content is running, other applications cannot read the log file. Thus never use Set-Content to log long running commands.

Encoding

Out-File saves in the Unicode (UTF-16LE) encoding by default (though this can be specified), whereas Set-Content defaults to ASCII (US-ASCII) in PowerShell 3+ (this may also be specified). In earlier PowerShell versions, Set-Content wrote content in the Default (ANSI) encoding.

^{Editor’s note: PowerShell as of version 5.1 still defaults to the culture-specific Default (“ANSI”) encoding, despite what the documentation claims. If ASCII were the default, non-ASCII characters such as ü would be converted to literal ?, but that is not the case: 'ü' | Set-Content tmp.txt; (Get-Content tmp.txt) -eq '?' yields $False.}

PS > $null | out-file outed.txt
PS > $null | set-content set.txt
PS > md5sum *
f3b25701fe362ec84616a93a45ce9998 *outed.txt
d41d8cd98f00b204e9800998ecf8427e *set.txt

This means the defaults of two commands are incompatible, and mixing them will corrupt text, so always specify an encoding.

Formatting

As Bartek explained, Out-File saves the fancy formatting of the output, as seen in the terminal. So in a folder with two files, the command dir | out-file out.txt creates a file with 11 lines.

Whereas Set-Content saves a simpler representation. In that folder with two files, the command dir | set-content sc.txt creates a file with two lines. To emulate the output in the terminal:

PS > dir | ForEach-Object {$_.ToString()}
out.txt
sc.txt

I believe this formatting has a consequence for line breaks, but I can’t describe it yet.

File creation

Set-Content doesn’t reliably create an empty file when Out-File would:

In an empty folder, the command dir | out-file out.txt creates a file, while dir | set-content sc.txt does not.

Pipeline Variable

Set-Content takes the filename from the pipeline; allowing you to set a number of files’ contents to some fixed value.

Out-File takes the data as from the pipeline; updating a single file’s content.

Parameters

Set-Content includes the following additional parameters:

• Exclude
• Filter
• Include
• PassThru
• Stream
• UseTransaction

Out-File includes the following additional parameters:

• Append
• NoClobber
• Width

For more information about what those parameters are, please refer to help; e.g. get-help out-file -parameter append.