Question

How can I rename each file in folder:

pattern is: (first part of file name).digit_(endoffilename)

for example

a.1_f
b.2_f
c.3_g

I would like to replace it with

a.01_f
b.02_f
c.03_ g

…

Thanks for help

Answer 1

Try this:

Get-ChildItem | Where {!$_.PSIsContainer} | 
    Rename-Item -NewName {$_ -replace '([^.]+)\.(\d)(\w)', '$1.0$2$3'} -wh

Or if you have more than nine files:

gci | ? {!$_.PSIsContainer -and $_.Name -match '([^.]+\.)(\d)(\w+)'} |  
  rni -NewName {$matches[1] + ("{0:00}" -f [int]$matches[2]) + $matches[3]} -wh

The second example uses aliases to shorten the command (easier for typing). gci is the alias for Get-ChildItem, ? is the alias for Where-Object and rni is the alias for Rename-Item. The -wh invokes the WhatIf functionality where PowerShell will show you what it would do so you can twiddle with the command until you’re happy with what the results would be. Then remove the -wh to actually execute it.