find and replace special characters powershell

Question

I have a method that has an if statement that catches if it finds a special character. What I want to do now if find the position of the special characters and replace it with _A

Some Examples

• test# becomes test_A

• I#hope#someone#knows#the#answer# becomes I_Ahope_Asomeone_Aknows_Athe_Aanswer_A

or if it has more than one special character

• You?didnt#understand{my?Question# becomes You_Adidnt_Aunderstand_Amy_AQuestion_A

Would I have to loop through the whole string and when I reach that character change it to _A or is there a quicker way of doing this?

Answer 1

# is just a character like any other, you can use the -replace operator:

PS C:\>'I#hope#someone#knows#the#answer#' -replace '#','_A'
I_Ahope_Asomeone_Aknows_Athe_Aanswer_A

Regex is magic, you can define all the special cases you like (braces will have to be escaped):

PS C:\>'You?didnt#understand{my?Question#' -replace '[#?\{]','_A'
You_Adidnt_Aunderstand_Amy_AQuestion_A

So your function could look something like this:

function Replace-SpecialChars {
    param($InputString)

    $SpecialChars = '[#?\{\[\(\)\]\}]'
    $Replacement  = '_A'

    $InputString -replace $SpecialChars,$Replacement
}

Replace-SpecialChars -InputString 'You?didnt#write{a]very[good?Question#'

If you are unsure of which characters to escape, have the regex class do it for you!

function Replace-SpecialChars {
    param(
        [string]$InputString,
        [string]$Replacement  = "_A",
        [string]$SpecialChars = "#?()[]{}"
    )

    $rePattern = ($SpecialChars.ToCharArray() |ForEach-Object { [regex]::Escape($_) }) -join "|"

    $InputString -replace $rePattern,$Replacement
}

Alternatively, you can use the .NET string method Replace():

'You?didnt#understand{my?Question#'.Replace('#','_A').Replace('?','_A').Replace('{','_A')

But I feel the regex way is more concise