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I am writing a script for customising a configuration file. I want to replace multiple instances of strings within this file, and I tried using powershell to do the job. It works fine for a single replace, but doing multiple replaces is very slow because each time it has to parse the whole file again, and this file is very large. The script looks like this:

$original_file = 'path\filename.abc'
$destination_file =  'path\filename.abc.new'
(Get-Content $original_file) | Foreach-Object {
    $_ -replace 'something1', 'something1new'
    } | Set-Content $destination_file

What I want is something like this, but I don't know how to write it:

$original_file = 'path\filename.abc'
$destination_file =  'path\filename.abc.new'
(Get-Content $original_file) | Foreach-Object {
    $_ -replace 'something1', 'something1aa'
    $_ -replace 'something2', 'something2bb'
    $_ -replace 'something3', 'something3cc'
    $_ -replace 'something4', 'something4dd'
    $_ -replace 'something5', 'something5dsf'
    $_ -replace 'something6', 'something6dfsfds'
    } | Set-Content $destination_file
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3 Answers

up vote 46 down vote accepted

One option is to chain the -replace operations together. The ` at the end of each line escapes the newline, causing PowerShell to continue parsing the expression on the next line:

$original_file = 'path\filename.abc'
$destination_file =  'path\filename.abc.new'
(Get-Content $original_file) | Foreach-Object {
    $_ -replace 'something1', 'something1aa' `
       -replace 'something2', 'something2bb' `
       -replace 'something3', 'something3cc' `
       -replace 'something4', 'something4dd' `
       -replace 'something5', 'something5dsf' `
       -replace 'something6', 'something6dfsfds'
    } | Set-Content $destination_file

Another option would be to assign an intermediate variable:

$x = $_ -replace 'something1', 'something1aa'
$x = $x -replace 'something2', 'something2bb'
...
$x
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Thanks, this is the method I used. –  Ivo Bosticky Aug 5 '10 at 13:18
 
+1 I am using it too :) –  cad Jul 18 '12 at 11:47
 
Can $original_file == $destination_file? As in I am modifying the same file as my source? –  cquadrini May 8 at 2:58
 
Because of the way PowerShell cmdlets stream their input/ouput, I don't believe it would work to write out to the same file in the same pipeline. However, you could do something like $c = Get-Content $original_file; $c | ... | Set-Content $original_file. –  dahlbyk May 10 at 13:34
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up vote 4 down vote

to get the post by George Howarth working properly with more than one replacement you need to remove the break, assign the output to a variable ($line) and then output the variable.

$lookupTable = @{
'something1' = 'something1aa' 
'something2' = 'something2bb' 
'something3' = 'something3cc' 
'something4' = 'something4dd' 
'something5' = 'something5dsf' 
'something6' = 'something6dfsfds'
}

$original_file = 'path\filename.abc'
$destination_file =  'path\filename.abc.new'

Get-Content -Path $original_file | ForEach-Object { 
    $line = $_

    $lookupTable.GetEnumerator() | ForEach-Object {
        if ($line -match $_.Key)
        {
            $line = $line -replace $_.Key, $_.Value
        }
    }
   $line
} | Set-Content -Path $destination_file
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up vote 1 down vote

Assuming you can only have one 'something1' or 'something2' etc per line, you can use a lookup table:

$lookupTable = @{
    'something1' = 'something1aa' 
    'something2' = 'something2bb' 
    'something3' = 'something3cc' 
    'something4' = 'something4dd' 
    'something5' = 'something5dsf' 
    'something6' = 'something6dfsfds'
}

$original_file = 'path\filename.abc'
$destination_file =  'path\filename.abc.new'

Get-Content -Path $original_file | ForEach-Object { 
    $line = $_

    $lookupTable.GetEnumerator() | ForEach-Object {
        if ($line -match $_.Key)
        {
            $line -replace $_.Key, $_.Value
            break
        }
    }
} | Set-Content -Path $destination_file

If you can have more than one of those, just remove the break in the if statement.

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