如何使用PowerShell在模式之前将每个逗号替换为文本文件中的空格

Question

I have a text file with lines in this format:

FirstName,LastName,SSN,$x.xx,$x.xx,$x.xx
FirstName,MiddleInitial,LastName,SSN,$x.xx,$x.xx,$x.xx

The lines could be in either format. For example:

Joe,Smith,123-45-6789,$150.00,$150.00,$0.00
Jane,F,Doe,987-65-4321,$250.00,$500.00,$0.00

I want to basically turn everything before the SSN into a single field for the name thus:

Joe Smith,123-45-6789,$150.00,$150.00,$0.00
Jane F Doe,987-65-4321,$250.00,$500.00,$0.00

How can I do this using PowerShell? I think I need to use ForEach-Object and at some point replace "," with " ", but I don't know how to specify the pattern. I also don't know how to use a ForEach-Object with a $_.Where so that I can specify the "SkipUntil" mode.

Thanks very much!

Answer 1

Mathias is correct; you want to use the -replace operator, which uses regular expressions. I think this will do what you want:

$string -replace ',(?=.*,\d{3}-\d{2}-\d{4})',' '

The regular expression uses a lookahead (?=) to look for any commas that are followed by any number of any character (. is any character, * is any number of them including 0) that are then followed by a comma immediately followed by a SSN (\\d{3}-\\d{2}-\\d{4}). The concept of "zero-width assertions", such as this lookahead, simply means that it is used to determine the match, but it not actually returned as part of the match.

That's how we're able to match only the commas in the names themselves, and then replace them with a space.

Answer 2

I know it's answered, and neatly so, but I tried to come up with an alternative to using a regex - count the number of commas in a line, then replace either the first one, or the first two, commas in the line.

But strings can't count how many times a character appears in them without using the regex engine(*), and replacements can't be done a specific number of times without using the regex engine(**), so it's not very neat:

$comma = [regex]","
Get-Content data.csv | ForEach { 

    $numOfCommasToReplace = $comma.Matches($_).Count - 4
    $comma.Replace($_, ' ', $numOfCommasToReplace)

} | Out-File data2.csv

Avoiding the regex engine entirely, just for fun, gets me things like this:

Get-Content .\data.csv | ForEach { 

    $1,$2,$3,$4,$5,$6,$7 = $_ -split ','
    if ($7) {"$1 $2 $3,$4,$5,$6,$7"} else {"$1 $2,$3,$4,$5,$6"}

} | Out-File data2.csv

---

(*) ($line -as [char[]] -eq ',').Count

(**) while ( #counting ) { # split/mangle/join }