How can i replace multiple lines in a text file using Powershell?

Question

I have a file and i can get 2 lines in the file.I have a file with the following content.

public class Websites
{
    //private const string URL = "https://au.yahoo.com/?p=us";
    private const string URL = "https://www.google.com/";
    //private const string URL = "https://stackoverflow.com/";
          ....

I can get the 2 lines individually like so:

$linegoogle = Get-Content "C:\myfile.cs" | Select-String "https://www.google.com/" | Select-Object - 
ExpandProperty Line
$google = $linegoogle.Trim()

$linestackoverflow = Get-Content "C:\myfile.cs" | Select-String "https://stackoverflow.com/" | 
Select-Object -ExpandProperty Line
$stackoverflow = $linestackoverflow.Trim()

But what i wabn to do is the following:

if (condition1)
{
    //replace the 2 lines  with
      
      // private const string URL = "https://www.google.com/";  
     private const string URL = "https://stackoverflow.com/";
}
else if (condition 2)
{
         //replace the 2 lines with

          private const string URL = "https://www.google.com/"; 
         // private const string URL = "https://stackoverflow.com/";
}

Are you sure you want to edit source files like so? Why not put urls in a config file instead? — vonPryz
– vonPryz, Commented Nov 23, 2020 at 8:10
Does this answer your question: use of the switch statement: stackoverflow.com/a/58182017/1701026 — iRon
– iRon, Commented Nov 23, 2020 at 10:33

Theo · Accepted Answer · 2020-11-23 14:41:12Z

Certainly not an elegant solution, but this might do it for you:

# set the condition here. 
# can be either 'stackoverflow', 'google' or 'yahoo' as per your example file.
$condition = 'stackoverflow'

# read the file as single multiline string
$content = Get-Content "C:\myfile.cs" -Raw
# do the replacements depending on what is in $condition
$result  = switch ($condition) {
    'stackoverflow' {
        $content -replace '(?m)^(\s+)(private const string URL = "https://www\.google\.com/.*";)', '$1//$2' -replace
                          '(?m)^(\s+)(private const string URL = "https://au\.yahoo\.com/.*";)', '$1//$2' -replace
                          '(?m)^(\s+)//(private const string URL = "https://stackoverflow\.com/.*";)', '$1$2'
    }
    'google' {
        $content -replace '(?m)^(\s+)(private const string URL = "https://stackoverflow\.com/.*";)', '$1//$2' -replace
                          '(?m)^(\s+)(private const string URL = "https://au\.yahoo\.com/.*";)', '$1//$2' -replace
                          '(?m)^(\s+)//(private const string URL = "https://www\.google\.com/.*";)', '$1$2'
    }
    'yahoo' {
        $content -replace '(?m)^(\s+)(private const string URL = "https://stackoverflow\.com/.*";)', '$1//$2' -replace
                          '(?m)^(\s+)(private const string URL = "https://www\.google\.com/*";)', '$1//$2' -replace
                          '(?m)^(\s+)//(private const string URL = "https://au\.yahoo\.com/.*";)', '$1$2'
    }
}

# show the result on screen
$result

# write back to file
$result | Set-Content -Path "C:\myfile.cs"

Remember that -replace uses regex, so you need to escape the special characters in the urls (in this case, only the dots) with a backslash. Also append .* after the last slash in the urls to account for any possible querystrings.

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