TOPIC: REN
Smarter file renaming using PowerShell
14th November 2014It appears that the Rename-Item commandlet in PowerShell is a very useful tool when it comes to smarter renaming of files. Even text substitution is a possibility, and what follows is an example that takes the output of the Dir command for listing the files in a directory and replaces hyphens with underscores in each one.
Dir | Rename-Item –NewName { $_.name –replace “-“,”_” }
The result is that something like the-file.txt becomes the_file.txt. This behaviour is reminiscent of the rename command found on Linux and UNIX systems, where regular expressions can be used, like in the following example that has the same result as the above:
rename 's/-/_/g' *
In both cases, you do need to be careful as to what files are in a directory for this, though the wildcard syntax on Linux or UNIX will be more familiar to anyone who has worked with files via almost any command line. Another thing to watch in the UNIX world is that * parses the whole directory structure, and that could be something that is not wanted for much of the time.
All of this is a far cry from the capabilities of the ren or rename command used in the days of MS-DOS and what has become the legacy Windows command line. Apart from simple renaming, any attempt at tweaking a filename through substitution ended up with the extra string getting appended to filenames when I tried it. Thus, the PowerShell option looks better in comparison.
Changing file timestamps using Windows PowerShell
29th October 2014Recently, a timestamp got changed on an otherwise unaltered file on me and I needed to change it back. Luckily, I found an answer on the web that used PowerShell to do what I needed, and I am recording it here for future reference. The possible commands are below:
$(Get-Item temp.txt).creationtime=$(Get-Date "27/10/2014 04:20 pm")
$(Get-Item temp.txt).lastwritetime=$(Get-Date "27/10/2014 04:20 pm")
$(Get-Item temp.txt).lastaccesstime=$(Get-Date "27/10/2014 04:20 pm")
The first of these did not interest me, since I wanted to leave the file creation date as it was. The last write and access times were another matter because these needed altering. The Get-Item commandlet brings up the file, so its properties can be set. Here, these include creationtime, lastwritetime and lastaccesstime. The Get-Date commandlet reads in the provided date and time for use in the timestamp assignment. While PowerShell itself is case-insensitive, I have opted to show the camel case that is produced when you are tabbing through command options for the sake of clarity.
The Get-Item and Get-Date have aliases of gi and gd, respectively, and the Get-Alias commandlet will show you a full list while Get-Command (gcm) gives you a list of commandlets. Issuing the following gets you a formatted list that is sent to a text file:
gcm | Format-List > temp2.txt
There is some online help, but it is not quite as helpful as it ought to be, so I have popped over to Microsoft Learn whenever I needed extra enlightenment. Here is a command that pops the full thing into a text file:
Get-Help Format-List -full > temp3.txt
In fact, getting a book might be the best way to find your way around PowerShell because of all its commandlets and available objects.
For now, other commands that I have found useful include the following:
Get-Service | Format-List
New-Item -Name test.txt -ItemType "file"
The first of these gets you a list of services, while the second creates a new blank text file for you, and it can create new folders for you too. Other useful commandlets are below:
Get-Location (gl)
Set-Location (sl)
Copy-Item
Remove-Item
Move-Item
Rename-Item
The first of the above is like the cwd or pwd commands that you may have seen elsewhere, in that the current directory location is given. Then, the second will change your directory location for you. After that, there are commandlets for copying, deleting, moving and renaming files. These also have aliases, so users of the legacy Windows command line or a UNIX or Linux shell can use something that is familiar to them.
Little fixes like the one with which I started this piece are all good to know, but it is in scripting that PowerShell really is said to show its uses. Having seen the usefulness of such things in the world on Linux and UNIX, I cannot disagree with that, and PowerShell has its own IDE too. That may be just as well, given how much there is to learn. That especially is the case when you might need to issue the following command in a PowerShell session opened using the Run as Administrator option just to get the execution as you need it:
Set-ExecutionPolicy RemoteSigned
Issuing Get-ExecutionPolicy will show you if this is needed when the response is: Restricted. A response of RemoteSigned shows you that all is in order, though you need to check that any script you then run has no nasty payload in there, which is why execution is restrictive in the first place. This sort of thing is yet another lesson to be learnt with PowerShell.
Creating empty text files and changing file timestamps using Windows Command Prompt & Powershell
17th May 2013Linux and UNIX have the touch command for changing the creation dates and times for files. However, it also creates empty text files for you as well. In fact, there are times when I feel the need to do this sort of thing on Windows too and the following command accomplishes the deed when run in a Command Prompt window:
type nul > command.bat
Essentially, null output is sent to a file that is created anew, command.bat in this case. Then, you can edit it in Notepad (or whatever is your choice of text editor) and add in what you need. This will not work in PowerShell, so you need another command for that:
New-Item command.bat -type file1
This uses the New-Item command, which also can be used to create folders as well if you so desire. Then, the command becomes the following:
New-Item c:\commands -type directory1
Note that file1 in the previous example has become directory1 and there is the -force option should you need to overwrite what already exists for some reason...
That other use of the UNIX/Linux touch command can be performed from the Command Prompt too, and here is an example command:
copy /b file.txt +,,
The /b switch switches on binary behaviour for the copy command, though that appears to be the default action anyway. The + operator triggers concatenation and ,, gets around not having a defined destination because you cannot copy a file over itself. If that were possible, then there would no need for special syntax for changing the date and time for a file.
For doing the same thing with PowerShell, try the following:
(GetChildItem test.txt).LastWriteTime=Get-Date
The GetChildItem command has aliases of gci, dir and ls and the last two of these give away its essential purpose. Here, it is used to pick out the test.txt file so that its timestamp can be replaced with the current date and time returned by the Get-Date command. The syntax looks a little more complex, even if it achieves the same end. Somehow, that touch command is easier to explain. Are Linux and UNIX that complicated, after all?
Renaming multiple files in Linux
19th August 2012The Linux and UNIX command mv has a number of limitations, such as not overwriting destination files and not renaming multiple files using wildcards. The only solution to the first that I can find is one that involves combining the cp and rm commands. For the second, there's another command: rename. Here's an example like what I used recently:
rename s/fedora/fedora2/ fedora.*
The first argument in the above command is a regular expression much like what Perl is famous for implementing; in fact, it is Perl-compatible ones (PCRE) that are used. The s before the first slash stands for substitute, with fedora being the string that needs to be replaced and fedora2 being what replaces it. The third command is the file name glob that you want to use, fedora.* in this case. Therefore, all files in a directory named fedora will be renamed fedora2 regardless of the file type. The same sort of operation can be performed for all files with the same extension when it needs to be changed, htm to html, for instance. Of course, there are other uses, but these are handy ones to know.
Filename autocompletion on the command line
19th October 2007The Windows 2000 command line feels an austere primitive when compared with the wonders of the UNIX/Linux equivalent. Windows XP feels a little better, and PowerShell is another animal altogether. With the latter pair, you do get file or folder autocompletion upon hitting the TAB key. What I didn't realise until recently was that continued tabbed cycled through the possibilities; I was hitting it once and retyping when I got the wrong folder or file. I stand corrected. With the shell in Linux/UNIX, you can get a listing of possibilities when you hit TAB for the second time and the first time only gives you completion as far as it can go with certainty; you'll never get to the wrong place, though you may not get anywhere at all. This works for bash, but not ksh88 as far as I can see. It's interesting how you can take two different approaches to reach the same end.