TOPIC: POWERSHELL
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?
Saving Windows Command Prompt & Powershell command history to a file for later useage
15th May 2013It's remarkable what ideas Linux gives that you wouldn't encounter that clearly in the world of Windows. One of these is output and command line history, so a script can be created. In the Windows world, this would be called a batch file. Linux usefully has the history command, and it does the needful for taking a snapshot like so:
history > ~/commands.sh
All the commands stored in a terminal's command history get stored in the commands.sh in the user's home area. The command for doing the same thing from the Windows command line is not as obvious because it uses the doskey command that is intended for command line macro writing and execution. Usefully, it has a history option that tells it to output all the commands issued in a command line session. Unless, you create a file with them in there, there appears to be no way to store all those commands across sessions, unlike UNIX and Linux. Therefore, a command like the following is a partial solution that is more permanent than using the F7 key on your keyboard:
doskey /history > c:\commands.bat
Windows PowerShell has something similar too, and it even has aliases of history and even h. All PowerShell scripts have file extensions of ps1 and the example below follows that scheme:
get-history > c:\commands.ps1
However, I believe that even PowerShell doesn't carry over command history between sessions, though Microsoft is working on adding this useful functionality. While they could co-opt Cygwin of course, that doesn't seem to be their way of going about things.
Shell swapping in Windows: PowerShell and the legacy command prompt
28th April 2010Until the advent of PowerShell, Windows had been the poor relation when it came to working from the command line when compared with UNIX, Linux and so on. A recent bit of fiddling had me trying to run FTP from the legacy command prompt when I ran into problems with UNC address resolution (it's unsupported by the old technology) and mapping of network drives. It turned out that my error 85 was being caused by an unavailable drive letter that the net use command didn't reveal as being in use. Reassuringly, this wasn't a Vista issue that I couldn't circumvent.
During this spot of debugging, I tried running batch files in PowerShell and discovered that you cannot run them there like you would from the old command prompt. In fact, you need a line like the following:
cmd /c script.bat
In other words, you have to call cmd.exe like perl.exe, wscript.exe and cscript.exe for batch files to execute. If I had time, I might have got to exploring the use ps1 files for setting up PowerShell commandlets, but that is something that needs to wait until another time. What I discovered though is that UNC addressing can be used with PowerShell without the need for drive letter mappings, not a bad development at all. While on the subject of discoveries, I discovered that the following command opens up a command prompt shell from PowerShell without any need to resort to the Start Menu:
cmd /k
Entering the exit command returns you to the PowerShell command line again, and entering cmd /? reveals the available options for the command, so you need never be constrained by your own knowledge or its limitations.
Running Windows 7 within VirtualBox
12th January 2009With all the fanfare that surrounded the public beta release of Windows 7, I suppose that the opportunity to give it a whirl was too good to miss. Admittedly, Microsoft bodged the roll-out by underestimating the level of interest and corralling everyone into a 24-hour time slot, with one exacerbating the other. In the event, they did eventually get their act together and even removed the 2.5 million licence limit. Thus, I suppose that they really needed to get 7 right after the unloved offering that was Vista, so they probably worked out that the more testers that they get, the better. After, it might be observed that the cynical view that the era of making people pay to "test" your products might be behind us and that users just want things to work well if not entirely faultlessly these days.
After several abortive raids, I eventually managed to snag myself a licence and started downloading the behemoth using the supplied download manager. I foresaw it taking a long time and so stuck with the 32-bit variant so as not to leave open the possibility of that part of the process using up any more of my time. As it happened, the download did take quite a few hours to complete, but this part of the process was without any incident or fuss.
Once the DVD image was downloaded, it was onto the familiar process of building myself a VirtualBox VM as a sandbox to explore the forthcoming incarnation of Windows. After setting up the ISO file as a virtual DVD, installation itself was an uneventful process, yet subsequent activities weren't without their blemishes. The biggest hurdle to be overcome was to get the virtual network adapter set up and recognised by Windows 7. The trick is to update the driver using the VirtualBox virtual CD as the source because Windows 7 will not recognise it using its own driver repository. Installing the other VirtualBox tools is a matter of going to Compatibility page in the Properties for the relevant executable, the one with x86 in the file name in my case, and setting XP as the Windows version (though Vista apparently works just as well, I played safe and depended on my own experience). While I was at it, I allowed the file to run under the administrator account, too. Right-clicking on executable files will bring you to the compatibility troubleshooter that achieves much the same ends but by a different route. With the Tools installed, all was workable rather than completely satisfactory. Shared folders have not worked for, but that might need a new version of the VirtualBox software or getting to know any changes to networking that come with Windows 7. I plan to stick with using USB drives for file transfer for the moment. Though stretching the screen to fit the VirtualBox window was another thing that would not happen, that's a much more minor irritation.
With those matters out of the way, I added security software from the list offered by Windows with AVG, Norton and Kaspersky being the options on offer. I initially chose the last of these but changed my mind after seeing the screen becoming so corrupted as to make it unusable. That set me to rebuilding the VM and choosing Norton 360 after the second Windows installation had finished. That is working much better, and I plan to continue my tinkering beyond this. I have noticed the inclusion of PowerShell and an IDE for the same, so that could be something that beckons. All in all, there is a certain solidity about Windows 7, though I am not so convinced of the claim of speedy startups at this stage. Time will tell and, being a beta release, it's bound to be full of debugging code that will not make it into the final version that is unleashed on the wider public.
Automating FTP II: Windows
15th April 2008Having thought about automating command line FTP on UNIX/Linux, the same idea came to me for Windows too, and you can achieve much the same results, even if the way of getting there is slightly different. The first route to consider is running a script file with the ftp command at the command prompt (you may need %windir%system32ftp.exe to call the right FTP program in some cases):
ftp -s:script.txt
The contents of the script are something like the following:
open ftp.server.host
user
password
lcd destination_directory
cd source_directory
prompt
get filename
bye
It doesn't take much to turn your script into a batch file that takes the username as its first input and your password as its second for the sake of enhanced security and deletes any record thereof for the same reason:
echo open ftp.server.host > script.txt
echo %1 >> script.txt
echo %2 >> script.txt
echo cd htdocs >> script.txt
echo prompt >> script.txt
echo mget * >> script.txt
echo bye >> script.txt
%windir%system32ftp.exe -s:script.txt
del script.txt
The feel of the Windows command line (in Windows 2000, it feels very primitive, but Windows XP is better and there's PowerShell now too) can leave a lot to be desired by someone accustomed to its UNIX/Linux counterpart, yet there's still a lot of tweaking that you can do to the above, given a bit of knowledge of the Windows batch scripting language. Any escape from a total dependence on pointing and clicking can only be an advance.
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.