Switch strings in a file - powershell

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. there will be a message box popup saying that value has been changed to [xxxxx] then background picture will be also changed accordingly.
$path = c:\work\test.xml
$A = AAAAA
$B = BBBBB
$settings = get-content $path
$settings | % { $_.replace($A, $B) } | set-content $path
I could not figured out how to use IF A then replace with B or IF B then replace A. Also, the code above will delete rest of contents in the file and only save the part that I modified back to the file.

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

Answer 2

This isn't tested extensively, but I think it should work:
path = c:\work\test.xml
$A = 'AAAAA'
$B = 'BBBBB'
[regex]$regex = "$A|$B"
$text =
Get-Content $path |
foreach {
$regex.Replace($text,{if ($args[0].value -eq $A){$B} else {$A}})
}
$text | Set-Content $path
Hard to be sure without knowing exactly what the data looks like.