change the name of multiple file for just a part of the filename

Question

I have 50 files with file names having the format like:

SIGMOID 01012019 - 01082019.XLS
SIGMOID 01012019 - 01022019.XLS

I would like to change it to:

SIGMOID_01012019 - 01082019.XLS
SIGMOID_01012019 - 01022019.XLS

I want to update part of the filename and add an underscore instead of just the first blank space in the name.

Thank you

I tried writing a script in powershell

dir |
Where-Object { $_.name.Contains(" ") } |
Rename-Item -NewName { $_.name -replace " ","_" }

but that updates every blank space.

Answer 1

Suppose you have files like:

SIGMOID 01012019 - 01082019.XLS
SIGMOID 01012019 - 01022019.XLS
SOMETHINGELSE    01012019 - 02022019.XLS
YETANOTHERPREFIX 01012019 - 03022019.XLS

then the following code will rename them:

$sourceFolder = 'THE PATH OF THE ROOTFOLDER THAT STORES THE XLS FILES TO RENAME'   #'#  enter your rootpath here
Get-ChildItem -Path $sourceFolder -File | 
    Where-Object { $_.Name -match '^\w+ +\d{8}.*\.xlsx?' } | 
    ForEach-Object { 
        $_ | Rename-Item -NewName ($_.Name -replace '^(\w+) +(\d{8}.*\.xlsx?)', '$1_$2') -WhatIf
    }

to become

SIGMOID_01012019 - 01082019.XLS
SIGMOID_01012019 - 01022019.XLS
SOMETHINGELSE_02012019 - 01022019.XLS
YETANOTHERPREFIX_03012019 - 01022019.XLS

Note: remove the -WhatIf if you feel happy with the results

Regex details:

^           Assert position at the beginning of a line (at beginning of the string or after a line break character)
(           Match the regular expression below and capture its match into backreference number 1
   \w       Match a single character that is a “word character” (letters, digits, etc.)
      +     Between one and unlimited times, as many times as possible, giving back as needed (greedy)
)           
\           Match the character “ ” literally
   +        Between one and unlimited times, as many times as possible, giving back as needed (greedy)
(           Match the regular expression below and capture its match into backreference number 2
   \d       Match a single digit 0..9
      {8}   Exactly 8 times
   .        Match any single character that is not a line break character
      *     Between zero and unlimited times, as many times as possible, giving back as needed (greedy)
   \.       Match the character “.” literally
   xls      Match the characters “xls” literally
   x        Match the character “x” literally
      ?     Between zero and one times, as many times as possible, giving back as needed (greedy)
)