Single match

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You can quickly determine if a text includes a specific pattern using Regex. There are multiple ways to work with Regex in PowerShell.

#Sample text
$text = @"
This is (a) sample
text, this is
a (sample text)
"@

#Sample pattern: Content wrapped in ()
$pattern = '\(.*?\)'

Using the -Match operator

To determine if a string matches a pattern using the built-in -matches operator, use the syntax 'input' -match 'pattern'. This will return true or false depending on the result of the search. If there was match you can view the match and groups (if defined in pattern) by accessing the $Matches-variable.

> $text -match $pattern
True

> $Matches

Name Value
---- -----
0    (a)

You can also use -match to filter through an array of strings and only return the strings containing a match.

> $textarray = @"
This is (a) sample
text, this is
a (sample text)
"@ -split "`n"

> $textarray -match $pattern
This is (a) sample
a (sample text)

Using Select-String

PowerShell 2.0 introduced a new cmdlet for searching through text using regex. It returns a MatchInfo object per textinput that contains a match. You can access it’s properties to find matching groups etc.

> $m = Select-String -InputObject $text -Pattern $pattern

> $m

This is (a) sample
text, this is
a (sample text)

> $m | Format-List *

IgnoreCase : True
LineNumber : 1
Line       : This is (a) sample
             text, this is
             a (sample text)
Filename   : InputStream
Path       : InputStream
Pattern    : \(.*?\)
Context    : 
Matches    : {(a)}

Like -match, Select-String can also be used to filter through an array of strings by piping an array to it. It creates a MatchInfo-object per string that includes a match.

> $textarray | Select-String -Pattern $pattern

This is (a) sample
a (sample text)

#You can also access the matches, groups etc.
> $textarray | Select-String -Pattern $pattern | fl *

IgnoreCase : True
LineNumber : 1
Line       : This is (a) sample
Filename   : InputStream
Path       : InputStream
Pattern    : \(.*?\)
Context    : 
Matches    : {(a)}

IgnoreCase : True
LineNumber : 3
Line       : a (sample text)
Filename   : InputStream
Path       : InputStream
Pattern    : \(.*?\)
Context    : 
Matches    : {(sample text)}

Select-String can also search using a normal text-pattern (no regex) by adding the -SimpleMatch switch.

Using [RegEx]::Match()

You can also use the static Match() method available in the .NET [RegEx]-class.

> [regex]::Match($text,$pattern)

Groups   : {(a)}
Success  : True
Captures : {(a)}
Index    : 8
Length   : 3
Value    : (a)

> [regex]::Match($text,$pattern) | Select-Object -ExpandProperty Value
(a)

Found a mistake? Have a question or improvement idea? Let me know.

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