--- title: "PowerShell and Regex: A Comprehensive Guide" description: "Learn how to use PowerShell and regex to match and replace text in your scripts with this in-depth tutorial." canonical: "https://adamtheautomator.com/powershell-regex/" --- # PowerShell and Regex: A Comprehensive Guide > Learn how to use PowerShell and regex to match and replace text in your scripts with this in-depth tutorial. Source: https://adamtheautomator.com/powershell-regex/ --- ATA Learning Tap to hide [ ATA Learning ](/) * [Home](/) * [Tutorials](/tutorials/) * [Instructors](/author/) * [Advertising](/advertising/) * [Recommended Resources](/resources/) * [About Adam](/about-adam/) Search for: * [](https://twitter.com/adbertram) * [](https://github.com/Adam-the-Automator) * [](https://www.linkedin.com/company/adam-the-automator-llc) * [](/feed/) ![PowerShell and Regex: A Comprehensive Guide](https://adamtheautomator.com/wp-content/uploads/2021/01/Getting-Started-with-PowerShell-and-Regex.jpg) # PowerShell and Regex: A Comprehensive Guide [![](https://secure.gravatar.com/avatar/d651a7bb1f4308be67d95c5cb50560ed0ee3e700256bd027cb08fbea6655b457?s=192&d=mm&r=g)Christopher Bisset](https://adamtheautomator.com/author/christopher-b/)5 January 20218 min. read Categories: [IT Ops](/category/it-ops/) Tags:[PowerShell](/tag/powershell/) Table of Contents * [Prerequisites](#h-prerequisites) * [Matching Simple Text with Select-String](#h-matching-simple-text-with-select-string) * [Select-String Output is a Rich Object](#h-select-string-output-is-a-rich-object) * [Using Capture Groups](#h-using-capture-groups) * [Using Capture Groups with Pattern Matches](#h-using-capture-groups-with-pattern-matches) * [A Practical PowerShell Regex Example](#h-a-practical-powershell-regex-example) * [The Match Operator](#h-the-match-operator) * [The Split Operator](#h-the-split-operator) * [ValidatePattern Parameter Validation](#h-validatepattern-parameter-validation) * [Replacing Text with PowerShell and Regex](#h-replacing-text-with-powershell-and-regex) * [Learning How to Write Better PowerShell Regex](#h-learning-how-to-write-better-powershell-regex) * [Don’t Use PowerShell and Regex if You Don’t Have To!](#h-don-t-use-powershell-and-regex-if-you-don-t-have-to) * [Moving on with Regex](#h-moving-on-with-regex) Understanding regular expressions (regex) can be a pain for us, humans, to understand but regex can be an incredibly powerful way to work with strings. In this article, you’re going to learn the basics of working with PowerShell and Regex. You’ll get an introduction to handy cmdlets like `Select-String`, learn about regex capture groups and get an intro to various regex parsing techniques. ## Prerequisites * A Windows 7 or later machine running PowerShell 5.1+. This article will be using **PowerShell** 7.1.0. ## Matching Simple Text with `Select-String` To demonstrate PowerShell and regex together, it’s always best to walk through an actual example. Let’s say you are gathering data from legacy machines about their hardware and, using the _wmic_ utility, you build a simple text file like below. We’ll call it _computername.txt_. ```powershell BiosCharacteristics={7,11,12,15,16,19,20,21,22,23,24,25,27,30,32,33,39,40,42,43} BIOSVersion={"ACRSYS - 2","V1.15","INSYDE Corp. - 59040115"} BuildNumber= Caption=V1.15 CodeSet= CurrentLanguage= Description=V1.15 EmbeddedControllerMajorVersion=1 EmbeddedControllerMinorVersion=15 IdentificationCode= InstallableLanguages= InstallDate= LanguageEdition= ListOfLanguages= Manufacturer=Insyde Corp. Name=V1.15 OtherTargetOS= PrimaryBIOS=TRUE ReleaseDate=20200826000000.000000+000 SerialNumber=NXHHYSA4241943017724S00 SMBIOSBIOSVersion=V1.15 SMBIOSMajorVersion=3 SMBIOSMinorVersion=2 SMBIOSPresent=TRUE SoftwareElementID=V1.15 SoftwareElementState=3 Status=OK SystemBiosMajorVersion=1 SystemBiosMinorVersion=15 TargetOperatingSystem=0 Version=ACRSYS - 2 ``` In this instance, let’s say that you need to extract the serial number of this computer. This serial number is located on the `SerialNumber=` line. In this situation, `Select-String` is going to be your new favorite tool. > _`Select-String` is a PowerShell cmdlet that allows you to provide a regular expression pattern and return a string that matches that pattern._ **_Related: [How to use PowerShell’s Grep (Select-String)](https://adamtheautomator.com/powershell-grep/)_** Since the pattern you’re looking for is in a file, you’ll first need to read that file and _then_ look for a regex match. To do that, provide a regex pattern using the `Pattern` parameter and the path to the text file using the `Path` parameter. ```powershell Select-String -Pattern "SerialNumber" -Path '.\computername.txt' ``` The `Select-String` cmdlet reads the _.\\computername.txt_ file attempts to find a set of characters matching `SerialNumber`. ![PowerShell and Regex : an example output of select-string](https://adamtheautomator.com/wp-content/uploads/2021/01/Untitled-2021-01-02T131135.139.png) PowerShell and Regex : an example output of select-string Believe it or not, you’re already using Regex. Regex, in its simplest form, is matching specific characters. In this situation, you are matching the literal “SerialNumber” phrase. However, you most likely do not want that whole line. Let’s instead start building a native script to retrieve _only_ the data you care about. ## `Select-String` Output is a Rich Object In the previous example, `Select-String` returned, what looked to be, a simple string but that output was actually a whole lot more. `Select-String` doesn’t just output a text match. The cmdlet actually returns a whole object. For example, specify a regex pattern of `This (is)` to search in the string `This is a string`. You can see below that if you pipe that output to `Get-Member`, `Select-String` returns a `Microsoft.PowerShell.Commands.MatchInfo` object. ```powershell select-string "This (is)" -inputobject "This is a String" | get-member ``` ![The properties of a select-string operation](https://adamtheautomator.com/wp-content/uploads/2021/01/Untitled-2021-01-02T131206.218.png) The properties of a select-string operation ## Using Capture Groups In the previous example, notice the regex pattern used (`This (is)`). This pattern contains a set of parenthesis. In a regular expression, those parentheses create a capture group. By surrounding a search term with parentheses, PowerShell is creating a capture group. [Capture groups](https://regexone.com/lesson/capturing_groups) “capture” the content of a regex search into a variable. Notice in the above example, `Select-String` outputs a property called `Matches`. This property contains all of the lines or values of capture groups (if using parentheses) found. The values of all capture groups are found under the `Matches.Groups` property. The`groups` property is an array of objects, within which the `value` property is the actual data. The `groups` array starts from 0 (with a value of the whole regex match), and increments by each capture group you specify in the Regex term. For the above example, you can extract both the whole string with the `matches` property, as well as the `is` match you extracted: ```powershell $match = select-string "This (is)" -inputobject "This is a String" #this property will match the whole select-string value $match.Matches.groups[0].value #this property will match the first capture group $match.Matches.groups[1].value ``` ![](https://adamtheautomator.com/wp-content/uploads/2021/01/Untitled-2021-01-02T131241.914.png) the output of a capture group ## Using Capture Groups with Pattern Matches Capturing a literal string is fairly pointless like capturing the literal `is` in `This is`. You’re not gaining valuable data from capturing a string you already knew the contents of. You can also combine capture groups with pattern matching, to extract _only_ the information you care about. _Pattern matching is using specially defined characters to match a range of characters, rather than a specific character. You can think of pattern matching as a wildcard `*` (like in notepad) on steroids._ Let’s say you want to match only the serial number in the line `SerialNumber=NXHHYSA4241943017724S00` and not the entire line. You’d like to capture _any_ character past the `SerialNumber=` phrase. You can extract that pattern by using the special dot `.` character, followed by a regex wildcard `*` (referred to as a Quantifier). The dot tells regex to match _any_ single character after `SerialNumber=`. The `*` tells regex to repeat the `.` match zero or more times. Combined with a capture group, the regex will look like `SerialNumber=(.*)`. You can see this below: ```powershell $string = "SerialNumber=numberwecareabout1042" #extract the serial number using a capture group $match = select-string "SerialNumber=(.*)" -inputobject $string #output the serial number $match.matches.groups[1].value ``` ![Using Capture Groups to extract important information](https://adamtheautomator.com/wp-content/uploads/2021/01/Untitled-2021-01-02T131325.748.png) Using Capture Groups to extract important information > _The special `.` character is only one of many different pattern match possibilities. You can match words, character ranges, number ranges, and the like. The Regex Reference category on the [regexr](https://regexr.com/) website (via the sidebar) is an excellent resource for different regex expressions._ ## A Practical PowerShell Regex Example Putting all of the above together, lets create a script that: 1. Ingests a list of text files (in the example, you will only grab the sample text file) 2. Loops through the text files, and find the serial number using `SerialNumber=(.*)` 3. Generates a hashtable that has a list of computer names, and their associated serial numbers ```powershell #Create a hashtable to hold the serial numbers $serialNumbers = @{} #Get all of the text files. In this case, you are limiting your scope to a single text file $files = Get-ChildItem "$pwd\computername.txt" #populate the hashtable foreach ($file in $files) { #first, retrieve that same string, like in the first example. This time, also capture the information after the label in a capture group $serialNumber = select-string "SerialNumber=(.*)" $file.FullName #now, use the capture group to extract the serial number only. This is done using the special matches property. We also use the filename (without extension) as the index for the serial number $serialNumbers[$file.basename] = $serialNumber.matches.groups[1].value } # write the output of the hashtable to the screen $serialNumbers | format-table ``` You can see the above script in action below using `computername.txt`: ![output of the above code](https://adamtheautomator.com/wp-content/uploads/2021/01/Untitled-2021-01-02T131416.024.png) output of the above code ## The `Match` Operator You’ve learned how to use `Select-String` to match regex patterns in text but PowerShell also has a few handy operators that support regex. One of the most useful and popular PowerShell regex operators is the `match` and `notmatch` operators. These operators allow you to test whether or not a string contains a specific regex pattern. If the string _does_ match the pattern, the `match` operator will return a True value. If not, it will return a False value. The opposite is true for the `notmatch` operator. Below you will see a simple example of this behavior in action. ```powershell #example of using a match parameter if("my string" -match "string") { "string is in my string!" } ``` ## The `Split` Operator If you’d like to split strings on non-static character like a space, a comma or a tab, you can use the `split` operator. The `split` operator performs a regex match on a string and take a second action of splitting the string into one or more strings. The `split` operator “converts” a string into an array of strings split on a specific regex pattern. ```powershell #create an array of strings split by the "\" symbol. The "\" is escaped within split because it is a special character "somebody\once told me\the world\is going\to roll me" -split ("\\") ``` ## `ValidatePattern` Parameter Validation PowerShell’s regex support doesn’t just end at cmdlets and operators; you can also integrate regex matching in parameters too. **_Related: [Everything you Ever Wanted to Know about PowerShell Parameters](https://adamtheautomator.com/powershell-parameter/#Parameter_Validation_Attributes)_** Using the `ValidatePattern` parameter validation attribute, you can validate string parameter values based on a regex pattern. This validation routine is useful to limit what input a user can use for a parameter value. ```powershell #example validation using regex. The ValidatePattern in this function will #only accept lowercase or uppercase alphabetical letters, as well as spaces. #the ^ at the start of the regex represents the start of the string, and $ at the end #represents the end of the string (to match the *entire* string). The + #means that the string must have one or more characters to be accepted function alphaOnly { param([ValidatePattern('^[a-zA-Z ]+$')][string]$alphaCharacters) write-output $alphaCharacters } #this will succeed alphaOnly "Hi Mom" #this will fail alphaOnly "Hi Mom!" ``` ## Replacing Text with PowerShell and Regex In the previous sections, you learned a few different ways to match patterns with PowerShell and regex. You can take that knowledge one step further and also _replace_ text that PowerShell has matched. One popular method to replace text with regex is to use the `-replace` operator. The `-replace` operator takes two arguments (separated by a comma) and allows you to use regex to replace a string with a replacement. `-replace` also supports capture groups, allowing you to match a capture group in the search and use the match in the replacement. For example, using `-replace` you can append text to a serial number: ```powershell $string = "SerialNumber=numberwecareabout1042" $currentYear = "2020" #append the year to the end of the serialnumber $serialNumber = $string -replace "SerialNumber=(.*)","SerialNumber=`$1-$currentYear" write-output $serialNumber ``` ![Appending text using the -replace operator and capture groups](https://adamtheautomator.com/wp-content/uploads/2021/01/Untitled-2021-01-02T131538.933.png) Appending text using the -replace operator and capture groups > _Note that in the above example, The dollar sign in `$1` is escaped using a backtick. Otherwise, PowerShell would treat that `$1` as a variable instead of a special regex character._ ## Learning How to Write Better PowerShell Regex All of the above might sound complicated, and, well, it is. In fact, there are lots of regex features _not_ covered in the above example. Luckily regex is a widely used method of machine reading, and there are tons of utilities to help learn how to effectively use regex. * [_RegexOne_](https://regexone.com/) is considered the de facto resource for learning regex. Regexone introduces the capabilities of regex in a bite sized and interactive way, letting you learn regex as you write it. RegexOne is a fantastic resource to begin learning how regex works from the beginning * [_Regexr_](https://regexr.com/) is one of the best tools out there to validate and build your regex. Aside from having a great real-time regex testing tool, regexr also includes a cheatsheet and a fantastic documentation engine. * [_Regexstorm_](http://regexstorm.net/tester) specifically uses the .Net engine to drive its tool. The site doesn’t have all of the bells and whistles that sites like Regexr has, but it _will_ accurately test your regular expression the same way PowerShell does. Even if you use other tools to build your regex, you should always run the regex through regexstorm to make sure PowerShell will parse it correctly. ## Don’t Use PowerShell and Regex if You Don’t Have To! PowerShell works around objects. PowerShell is built around structured objects. Objects with properties are a lot easier to manage than loose text where regex comes into play. **_Related: [Back to Basics: Understanding PowerShell Objects](https://adamtheautomator.com/powershell-objects/)_** One of the main purposes of PowerShell and also structured languages like JSON is to make regex and text parsing obsolete. Human language is fantastic for regex to decipher, but generally, regex is something you try to _avoid_ when it comes to storing or transferring data. **_Related: [Wrangling REST APIs with PowerShell and JSON](https://adamtheautomator.com/powershell-json/)_** Some people even get [_worked up_](https://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags/1732454#1732454) over using regex on structured languages. If you can use an object-oriented method or a structured language like JSON, XML, etc over regex, do it! Even though you _can_ do just about anything with regex, doesn’t mean you should! ## Moving on with Regex With this article, you should now have a basic understanding of how regex helps machines parse and find text, even when looking for highly specific or complicated phrases. You should also have the tools to test, validate, and learn about regex in the context of PowerShell. If you haven’t done so, the [_RegexOne_](https://regexone.com/) tutorials are a fantastic next step. Test your regex knowledge and power up your string powers in PowerShell! 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