Guy's Scripting Ezine 133
PowerShell Script to List Files
PowerShell Script to List FilesThese examples explain how to get started with PowerShell. However, I dislike 'Hello World' examples, therefore my script has a practical use
namely, to get a listing of a particular type of file, in a particular directory tree.
♣
A year ago both Vista and PowerShell seemed like a distant dreams, now they are reality. Each had its development problems but the final
product is a huge improvement on XP and VBScript respectively. While many commentators do nothing but look for points to criticise, I view the well documented teething problems as a sign that we are still
at an exciting stage of computing. To amplify what I mean, let us compare improvements in Vista and PowerShell with improvements in my new Ford car. Is my new car more powerful than the previous model, does it do more MPG, is it more secure, is it more exciting? Sadly the answers
on all points were 'not really'. Ask the same questions about Vista or PowerShell and the answers were a resounding, 'Yes' for all questions. My only complaint is that as an IT
professional, I foolishly believe that I will soon master the new product. In reality it takes ages to become expert on a new IT sytem. The good news, at least for me, is that learning the new
features is exciting and brings out my pioneer spirit. My pure scripting task is to list all files with a given extension in a particular
directory tree. Specifically, all dlls in the windows\windows32 folder. This simple mission is much like typing the DOS command: dir \s. My learning agenda for PowerShell is as follows:
1) To appreciate the rhythm of the
PowerShell language. Verb-noun pairs.
2) To see how easy it is to introduce $variables
3) To employ the power of the pipe command (|) so that the output
of the first command becomes the input of a second command.
4) To interrogate the capabilities of an object with get-member.
Pre-requisites
You need to have already installed a local copy of PowerShell RC2. If necessary search the internet for 'Microsoft PowerShell download'. Note PowerShell RC2 is much changed from its
predecessor, release candidate 1. Instructions - Save the following script to a text file with a .ps1 extension, for example:
C: \Script\dll.ps1.
- Launch PowerShell and navigate to the folder where you saved the .ps1 file. The cd command works fine.
- To call for your script file, type at the command line PS> .\dll.ps1.
Note 1. The rhythm of the command is: dot slash filename.
Note 2. You don't have to type PS>
# PowerShell script to list the DLL files under the system32 folder
$Dir = get-childitem C:\windows\system32 -recurse
# $Dir |get-member
$List = $Dir | where {$_.extension -eq ".dll"}
$List |
format-table name
Learning PointsNote 1: Beginning a script with cls is one of my idiosyncrasies, it simply means clear the screen of any previous output. The hash symbol # means a remark, or do
not process this line. Note 2:
$Dir = get-childitem C:\windows\system32 -recurse
This command sets the variable $Dir to the path of the files we seek for our list. You have probably guessed the purpose of the -recurse
switch, to drill down to the sub-folders. Get-childitem is often abbreviated to its alias gci. Note 3: $List = $Dir | where {$_.extension -eq ".dll"}
$List is another variable whose
purpose is to filter the output, as a result we get only files with .dll extension. Pay particular attention to the construction $_. which means, in this pipeline. Also observe that instead of the
equals sign, PowerShell needs -eq. Note 4: One of PowerShell's features is the pipe symbol (|). Most PowerShell scripts contain at least one pipe to control, or filter the output of the
main command.
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in networks in two ways:
For Mr Organized there is a nifty subnet
calculator, you enter the network address and the subnet mask, then IPAT
works out the usable addresses and their ranges.
For Mr Lazy IPAT
discovers and then displays the IP addresses of existing computers.
Download the Free IP Address Tracker
The purpose of this script is to list the properties of the file object controlled by the $dir variable. When we display the list, how much information do we want? What file properties are
available? All is revealed by get-member.
# PowerShell script to list the DLL files under the system32 folder
$Dir = get-childitem C:\windows\system32 -recurse
$Dir |get-member
# $List = $Dir | where {$_.extension -eq ".dll"}
# $List
|ft fullname |out-file C:\scripts\dll.txt
# List | format-table name
Learning PointsNote 1: This is the same script as example 1, all that has changed is the #. I have 'remmed' out the list and activated the line: $Dir |get-member.
Note 2: Get-member lists the properties and methods of the PowerShell object $Dir. Once we have our list we can control the output specified by format-table. See next example.
Seeing the files on screen is
fine, but with lists of files, it's often handy to generate a file containing your script's output.
# PowerShell script to list the DLL files under the system32 folder
$Dir = get-childitem C:\windows\system32 -recurse
# $Dir |get-member
$List = $Dir | where {$_.extension -eq ".dll"}
$List
|ft fullname |out-file C:\Scripts\dll.txt
# List | format-table name
Learning PointsNote 1: Here is the line that I activated by removing the #. $List |ft fullname |out-file c: \Scripts\dll.txt. What this does is create a file in the c:
\Scripts folder. (Note it does not create the \Scripts folder itself, you must do that) In that dll.txt file are the names of all the files with a .dll extension. Note 2: ft,
meaning format-table, is one of the built-in aliases which make the code shorter to write.
Challenge 1: Set the script to list a different extension, for example .com or .exe.
Challenge 2: Persuade the script to output the 'length' property of the files.
Challenge 3: Filter the object property with -MemberType, for example remove unwanted Methods leaving only Property:
$Dir |get-member -MemberType property
PowerShell is a very efficient scripting language. In this example we use $variables and verb-noun
pairs to create a script which lists the files we seek. I hope you will tweak my examples to list the types of files that you need. Moreover, I hope that you can see how to adjust the variable,
as a result you can locate a directory tree of your choosing. As a bonus, Example 3 outputs the list of files, not to screen, but to a text file.
If you like this page then please share it with your friends
See more Microsoft PowerShell file tutorials:
• PowerShell Home •
Add-Content •
Get-Content •
Set-Content •
Test-Path •
-recurse
•
Files •
PowerShell Registry •
PowerShell ItemProperty •
Compare-object
•
Get-Credential •
Windows
PowerShell
Please email me if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.
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