Switch strings in a file

Question

I have a string needs to be changed in a file between two values. What I want to do is if I found value A then change to value B, if I found value B then change to value A.

Answer 1

Assuming that $A and $B contain just simple strings rather than regular expressions you could use a switch statement with wildcard matches:

$path = 'c:\work\test.xml'
$A = 'AAAAA'
$B = 'BBBBB'

(Get-Content $path) | % {
  switch -wildcard ($_) {
    "*$A*"  { $_ -replace [regex]::Escape($A), $B }
    "*$B*"  { $_ -replace [regex]::Escape($B), $A }
    default { $_ }
  }
} | Set-Content $path

The [regex]::Escape() makes sure that characters having a special meaing in regular expressions are escaped, so the values are replaced as literal strings.

If you're aiming for something a little more advanced, you could use a regular expression replacement with a callback function:

$path = 'c:\work\test.xml'
$A = 'AAAAA'
$B = 'BBBBB'

$rep = @{
  $A = $B
  $B = $A
}

$callback = { $rep[$args[0].Groups[1].Value] }

$re = [regex]("({0}|{1})" -f [regex]::Escape($A), [regex]::Escape($B))

(Get-Content $path) | % {
  $re.Replace($_, $callback)
} | Set-Content $path