Trying to create a simple backup PowerShell script

Question

Trying to create a simple backup script, but every time I run the script below, I receive the following error:

Copy-Item : Cannot overwrite the item C:\Users\Jacob\desktop\file1.txt with 
itself.
At C:\Users\Jacob\desktop\test.ps1:5 char:1
+ Copy-Item $file $file.backup
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : WriteError: (C:\Users\Jacob\desktop\file1.txt:String) [Copy-Item], IOException
    + FullyQualifiedErrorId : CopyError,Microsoft.PowerShell.Commands.CopyItemCommand

Simple script:

Param(
    [Parameter(Mandatory=$true)]
    [string]$file
)

Copy-Item $file $file.backup
"$file has been backed up."

Please do not edit an answer into the question. If you found a solution yourself it's perfectly acceptable to post it as an answer of your own. — Ansgar Wiechers
– Ansgar Wiechers, Commented Jan 26, 2018 at 18:51

Ansgar Wiechers · Accepted Answer · 2018-01-26 18:50:32Z

0

$file.backup tries to expand the (non-existing) property backup on the string variable $file. This comes back with an empty result, so you're effectively running Copy-Item $file (without a destination), which causes the error you observed.

To avoid this issue you can do several things, for instance:

define the destination as a string:
```
Copy-Item $file "${file}.backup"
```
append the extension by string concatenation:
```
Copy-Item $file ($file + '.backup')
```

use the format operator:

Copy-Item $file ('{0}.backup' -f $file)

answered Jan 26, 2018 at 18:50

Ansgar Wiechers

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