Regular Expression Characters

For a list of regular expression characters:
Get-Help About_Regular_Expressions

PowerShell regular expression characters:

PowerShell also supports the character classes from .NET regular expressions:

As well as the ,NET regular expression quantifiers:

Using Regular Expressions

The $Matches variable holds all the values that match the regular expression.

In this example we are looking for a single (the first) “word” character:

If we want to find multiple word characters we would do this:

$matches only holds the word “PowerShell” because the space is not a word character so the matching stops. To find more than one word we need to put a (literal) space between our word expressions:

We can do the same for numbers.

Or, to match more than one numeral:

To find an IP address, say in a log file:

So far we have only been matching one thing at a time. Using the .NET regex object gives us a lot more flexibility.

[regex] specifies that the expression “\w*” is not a string object but an object of type regex. Regex objects have a “matches” property that produces the output above. Notice that the word (or space) is contained in a “value property. We can see only the items matched, without the index, length, etc. by iterating through the matches and specifying only the value property.

Note that $var and $var1 are still populated from the previous example.

We have been populating strings to search through. We can also read text files and extract data from them. For example, here is a simple .CSV file with information about people.

Let’s extract the email addresses:

Sometimes we want to parse through several files at a time. Select-string makes that easy. The output is a bit different than what we’ve seen, so we’ll start out with one file to get used to how it works. Suppose we want to find “Fred” in our file?

Notice that there are three parts to the output separated by colons: the path (People.csv), the line number in the file (1), and the text of the line where “Fred” was found.

Here’s another .CSV file in the same folder:

Let’s look for email addresses in both files.

Or perhaps we’re just interested in which files email addresses were found in:

The –list parameter eliminates duplicate values from the output.