Extracting 6-digit numeric string from paragraph of text using PowerShell results in Blank data

Question

Trying to extract a 6 digit numeric string from a paragraph of text using PowerShell but it works only under one scenario. The 6 digit string sits inside a paragraph of text in the Windows Clipboard. In my code I'm expecting the variable $Matches[0] to be the 6 digits I'm looking for but the result is always blank. If I uncomment line 2 then $Matches[0] will always be whatever the 6 digit code in line 2 is, meaning 123456 as shown below. But if I comment out line 2, then copy a paragraph of text from my real world example, and re-run the code, instead of $Matches[0] being the expected 6 digit string, it is always blank. I will walk through both examples and their outputs below. Not sure what I am doing wrong.

Working Example:

$Matches[0] = $null
Set-Clipboard -value "Your PIN is 123456."
$PIN = (Get-Clipboard) -match '\d{6}'
# Get-Clipboard
Write-Output $Matches[0]

The above code will output the below, as expected:

Non-working Example: If I comment out line 2:

$Matches[0] = $null
# Set-Clipboard -value "Your PIN is 123456."
$PIN = (Get-Clipboard) -match '\d{6}'
# Get-Clipboard
Write-Output $Matches[0]

and given this paragraph of text, copied into the Windows Clipboard:

Hello,

Your authentication code is 351370

This code will expire in 20 minutes to keep your account secure.

The output shows blank, instead of the expected 351370:

Thoughts?

mklement0 · Accepted Answer · 2021-11-04 19:28:30Z

The problem:

The Get-Clipboard cmdlet returns multiline text as an array of strings.
With an array as the LHS, -match, the regular-expression matching operator acts as a filter, returning the subarray of matching elements (as other comparison operators do - see about_Comparison_Operators), and in this case the automatic $Matches variable is not populated.

The solution is to request the text on the clipboard as a single, multiline string, using the
-Raw switch:

if ((Get-Clipboard -Raw) -match '\d{6}') {
  $Matches[0] # -> '351370'
}

An alternative is to use -replace, the regex-based string-replacement operator, which requires matching the entire string and replacing it with what a capture group matched:

@'
Hello,

Your authentication code is 351370

This code will expire in 20 minutes to keep your account secure
'@ -replace '(?s).*(\d{6}).*', '$1' # -> 351370

Note:

Inline option s (SingleLine; ((?s)) ensures that . also matches newline (\n) characters, to enable matching across all lines of a multiline string.
In the replacement operand, $1 refers to what the first (and only) capture group ((...)) captured.
Caveat: if the regex does not match the input, the input string is returned as-is.

Finally, direct use of .NET APIs via the [regex] class (System.Text.RegularExpressions.Regex) is another alternative, as shown in santisq's answer, but it requires advanced knowledge outside the realm of PowerShell's own commands and operators.

Santiago Squarzon · Accepted Answer · 2021-03-12 21:15:19Z

2

PS C:\> Get-Clipboard
Hello,

Your authentication code is 351370

This code will expire in 20 minutes to keep your account secure.

PS C:\> ([regex]'\d{6}').Match((Get-Clipboard)).Value
351370

Edit: Sorry, I should explain at least a bit more. When using regex to search and match specific pattern within a string you can use .Match if you want the first appearance of your pattern or .Matches to find all appearances. Example:

PS C:\> $re=[regex]"\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b"

PS C:\> $re.match('string string string string string 
string string string 127.0.0.1 string string 
string 192.168.1.1 string string string string 
string string string 255.255.255.0 string string 
string string string string string string ').value

127.0.0.1

PS C:\> $re.matches('string string string string string 
string string string 127.0.0.1 string string 
string 192.168.1.1 string string string string 
string string string 255.255.255.0 string string 
string string string string string string ').value

127.0.0.1
192.168.1.1
255.255.255.0

edited Mar 12, 2021 at 21:15

answered Mar 12, 2021 at 20:59

Santiago Squarzon

65.5k5 gold badges26 silver badges59 bronze badges

2 Comments

mklement0 Over a year ago

That works, and showing the .Matches variant is a nice addition, given that -match only ever finds one match, but there's a caveat: Because Get-Clipboard returns a multiline string as an array of lines, passing an array to the .Match() method's string parameter causes PowerShell to stringify the array, which means joining the elements with spaces. For instance, if "line 1`nline 2" is on the clipboard, Get-Clipboard returns array 'line 1', 'line 2' and stringifies that to space-separated single-line string 'line 1 line 2', which can lead to false positives.

mklement0 Over a year ago

To illustrate the problem: ([regex] '1 l').Match(('line 1', 'line 2')).Success yields $true. You can make Get-Clipboard return a multiline string as-is with the -Raw switch, which is the only thing missing from T-Heron's own solution attempt with -match.

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