Check if string contains numeric value in PowerShell?

Question

I want to check if a string contains a numeric value. I have this code :

$string = "some string that contains 123456     in the middle"
$substring = $string.substring(27,9).Trim()

I have $substring which will be containing "123456" and I found this IsNumeric function here : In PowerShell, how can I test if a variable holds a numeric value?

The thing is that this when I'm extracting it from $string it acts like string type and IsNumeric returns false since it's comparing it to the all numeric types. and even tough it will contain a number the output of IsNumeric will be false.

Is there a better way to check if string contains numeric values?

Answer 1

The correct way to check if a given string can be turned into a number:

[string]$InString = "123456"
[Int32]$OutNumber = $null

if ([Int32]::TryParse($InString,[ref]$OutNumber)){
    Write-Host "Valid Number"
    $OutNumber
} else {
    Write-Host "Invalid Number"
    #error code here
}

then $OutNumber will contain the number as a numeric type.

Answer 2

In regex \d is the check for digits

\d* checks for 0 to infinite digits

\d? Checks for 0 to 1 digit

\d{0,5} checks for 0 to 5 digits

\d+ checks for 1 to infinite digits

^ is the beggining of a line

$ is the end of a line

So

^\d+$ will check for 1 or more digits from the beginning to the end of the line and only digits. Any other symbol will break the connection from beginning to end and not be found.

Answer 3

The traditional way using the .NET framework:

if( [Microsoft.VisualBasic.Information]::IsNumeric($myString) ) {
  # do something
}

Answer 4

using error

It's accepts decimal numbers too.

[string]$myString = "12.3456"
try{
    [int]$res=[int]1*$myString
    Write-Host "Valid Number"
}catch{
    Write-Host "Invalid Number"
}

Answer 5

use -match '\d'

string = "some string that contains 123456     in the middle"
$substring = $string.substring(27,9).Trim()
$substring -match '\d'

Answer 6

Using the -as type_operator is probably the most powershell way. It will return the number, or $null if it was not possible to convert. To keep the examples as short as possible I am using int but this will work for float and double as well. For example:

"0" -as [int]

If for some reason you only wanted to check if the string contains numeric data then you could simply test this against $null via ($null -ne ("0" -as [int]))

But it's probably far more likely that you will want to use the value once converted, if possible, which is easily done by just assigning the result to a variable then checking against $null:

$myNum = "0" -as [int]
if ($myNum -eq $null) {
    #is not numeric
} else {
    #is numeric
}

Using exceptions as program control is a very bad practice, and likely a guarantee that you will see a performance increase with this over that.

I haven't tested this assertion, but I think it is very likely you will also see a performance increase over the regex method posted as well, with the bonus of also having the number handy. You could use a regex with grouping to achieve the same thing, but nobody has posted that yet:

"0" -match "(?<num>\d*)"
$Matches.num

Plus you still have actually do the conversion:

$Matches.num.GetType()
([Int32]$Matches.num).GetType()