Currently I'm using cmdlets like:

dir | rename-item -NewName {$_.name -replace "-","_"}

But now I need to add a prefix to the filename for all files in the directory.
I can't predict how long each filename is (it varies), so I can't just use a bunch of . wildcards.

I need it to append a fixed phrase to the beginning of each filename, regardless what that filename is.

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    See solution here stackoverflow.com/a/20874916/5518385 – Yisroel Tech May 7 '17 at 22:53
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    What is it now? A prefix or a suffix? For a prefix you already got a name so (literally) just add to your prefix or (for a suffix) just add the suffix to it. – Seth May 8 '17 at 12:09

An alternative approach to a regular expression would be to use simple string operations to create the new file name.

Get-ChildItem | Rename-Item -NewName { "Prefix_" + $_.Name }
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    I'm trying this, but it seems to go mad and keep trying to prefix filenames over and over until it crashes from the filename being too long - e.g. running the command above results in filenames like Prefix_Prefix_Prefix_Prefix_Prefix_Prefix_Prefix_Prefix_Prefix_Prefix_... – Tom Carpenter Sep 2 '17 at 14:37
  • Split the command. $items = Get-ChildItem; And replace the Get-ChildItem in the above case with $items. – Seth Sep 6 '17 at 10:21
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    In the end based on this, I just added -Exclude Prefix_* to the Get-ChildItem command. – Tom Carpenter Sep 6 '17 at 10:23

You are quite near.

  • -replace uses RegEX and in a Regular Expression you anchor at the beginning with a ^
  • for a suffix you can similarly replace the anchor at line end with $
  • to avoid any possible re-iteration of the renamed file enclose the first element of the pipeline in parentheses.

(Get-ChildItem -File) | Rename-Item -NewName {$_.Name -replace "^","Prefix_"}
  • I like this answer because it doesn't cause an infinite loop and I don't need to write the prefix twice - like what happens in other solutions with the -Exclude Prefix_* to avoid the loop. – TCB13 Jul 16 '18 at 7:34

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