regex - PowerShell multiple string replacement efficiency

Question

I'm trying to replace 600 different strings in a very large text file 30Mb+. I'm current building a script that does this; following this Question:

Script:

$string = gc $filePath 
$string | % {
    $_ -replace 'something0','somethingelse0' `
       -replace 'something1','somethingelse1' `
       -replace 'something2','somethingelse2' `
       -replace 'something3','somethingelse3' `
       -replace 'something4','somethingelse4' `
       -replace 'something5','somethingelse5' `
       ...
       (600 More Lines...)
       ...
}
$string | ac "C:log.txt"

But as this will check each line 600 times and there are well over 150,000+ lines in the text file this means there’s a lot of processing time.

Is there a better alternative to doing this that is more efficient?

Answer 1

Combining the hash technique from Adi Inbar's answer, and the match evaluator from Keith Hill's answer to another recent question, here is how you can perform the replace in PowerShell:

# Build hashtable of search and replace values.
$replacements = @{
  'something0' = 'somethingelse0'
  'something1' = 'somethingelse1'
  'something2' = 'somethingelse2'
  'something3' = 'somethingelse3'
  'something4' = 'somethingelse4'
  'something5' = 'somethingelse5'
  'X:Group_14DACU' = '\DACU$'
  '.*[^xyz]' = 'oO{xyz}'
  'moresomethings' = 'moresomethingelses'
}

# Join all (escaped) keys from the hashtable into one regular expression.
[regex]$r = @($replacements.Keys | foreach { [regex]::Escape( $_ ) }) -join '|'

[scriptblock]$matchEval = { param( [Text.RegularExpressions.Match]$matchInfo )
  # Return replacement value for each matched value.
  $matchedValue = $matchInfo.Groups[0].Value
  $replacements[$matchedValue]
}

# Perform replace over every line in the file and append to log.
Get-Content $filePath |
  foreach { $r.Replace( $_, $matchEval ) } |
  Add-Content 'C:log.txt'