-replace will only work with "string", but not with $variable

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Daniela.M Posted: 09-13-2012 7:10 AM

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Hi,

I'm trying to read some replacement rules from a file (separated by "|") and use them on a given Text...

$inputText = [system.IO.File]::ReadAllText("input.txt")

$regex = Get-Content "changes.txt" -ReadCount 0

foreach($expression in $regex) {

 if ($expression -eq 'EOF') { break }

    $parts = $expression.Split("|")

 if ($parts.Count -eq 2) {

$t = $parts[0]

$u = $parts[1]

   $inputText = $InputText -creplace $t, $u

   $inputText | out-file "output.txt" -enc ascii

  }

 }

This works fine for most rules, but doesn't work for matching patterns at end of a line.

e.g. \\DE`r`n|\\DE_02`r`n

If I try using strings for the replacement, the expected replacements are done:

  $inputText = $InputText -creplace "\\DE`r`n", "\\DE_02`r`n"

How come it works with "strings", but not with &variables??? (the variables $t and $u contain just the same strings...)

Which replacement rule can be used for my needs?

Thanks in advance!

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nohandle replied on 09-14-2012 5:17 AM

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Hello,

your examples do not work for me, maybe I provide wrong input data. I assume you are trying to replace \\DE with \\DE_2  in the source file (but not replacing \\server\name\DE to \\server\name\DE_2) by providing the replace rules in changes file.

I have taken time to explain the script in more detail since you seem a bit lost, hope you'll appreciate it.

First of all there is  -replace (-split) operator and its case sensitive variant -creplace (-csplit), these are taking regular expression as argument, you have to realize that | and \ has special meaning in regular expressions.  

In your example $InputText -creplace "\\DE`r`n", "\\DE_02`r`n" does not mean replace \\DE<end of line> with \\DE_2<end of line> but replace \DE`n`r with \\DE_2`n`r. The first \ in the first expression is taken as an escape sign causing the second one to be interpreted as a normal character.

This beahviour can be supressed with "simplematch" option for the -split and with [regex]::escape("<expression>") method for the -replace operator.

(Btw what is the reason you use the -readCount  0 ?)

here is code that takes input file input.txt  and replaces strings by rules given in changes.txt file in format

find|replacewith<rest of line is ommited> 

find|replacewith<rest of line is ommited>

#set paths for the input, output and changes files
$changeFile = 'C:\Temp\regex_file\changes.txt'
$changes = Get-Content $changeFile
<#content:
\\DE|\\DE_02
\\FE|\\FE_02
test
#>
$InputFile = 'C:\Temp\regex_file\input.txt'
$input = Get-Content $InputFile
<#content:
\\DE
\\DE\name
\\DE\file\DE\
\\FE
\\FE\test\FE
#>
$outputFile = 'C:\Temp\regex_file\output.txt'

#process the data
<#for each line in changes files do a split by "|" and
produce maximum of 3 results for each line (do 3-1=2 splits, reducing amount of work done if
there is more places to split), simplematch - match the "|" as is,not using special regex characters)
If the count of results from the split is less than 2 then proceed to the next line 
(go to next item in foreach)
do a replace on the $input variable doing a "simpleMatch" - \\ are treated as normal characters
#>
foreach ($change in $changes) 
    {
        $change = $change -split "|",3,"simplematch"
        if ($change.Count -lt 2) {continue}
        $input = $input -creplace [regex]::Escape($change[0]), $change[1]
    }
$input | out-file $outputFile -enc ascii

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Daniela.M replied on 09-17-2012 3:05 AM

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Thank you a lot for your quick and detailed reply =)

Unfortunately your solution will not work for me. I'll try to explain a little better, what needs to be done:

I need to replace  \DE<end of line>  

but must not replace \DEUTSCHLAND or \DE\WHATEVER

Here's my Test-File:

At line 23 I inserted \DE for testing. This must not be replaced.

At line 1954 there is \DE at the end of a line. This should be replaced by \DE_02.

By the way, you're right, I am a bit lost... I don't know powershell very well, and I didn't write the script. Therefore I unfortunately don't know, why there's a -readCount 0

I hope it's a little clearer now, what I need to do and you can help me solve the problem.

Thanks for your time!

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nohandle replied on 09-17-2012 3:46 AM

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Ok, that is no problem:)

This one should work:

$changeFile = 'C:\Temp\regex_file\changes.txt'
$changes = Get-Content $changeFile
$InputFile = 'C:\Temp\regex_file\input.txt'
$input = Get-Content $InputFile
$outputFile = 'C:\Temp\regex_file\output.txt'

foreach ($change in $changes)
    {
        $change = $change -split "|",3,"simplematch"
        if ($change.Count -lt 2) {continue}
        $input = $input -creplace $change[0], $change[1]
    }
$input | out-file $outputFile -enc ascii

there is change to the code at this line:

it does no longer escape the string provided, so it is now treated as a regular expression

In regular expressions you mark end of line ($), also \ has a special meaning in regular expressions so we need to escape it by the escape sign \

the \s* means zero or more (*) whitespace (\s) characters - there are often extra spaces or tabs at end of line

you need to provide this in the changes file \\DE\s*$|\DE_02, the first one is regular expression, the second is just normal string.  

$input = $input -creplace $change[0], $change[1]

PS: If you need to apply just one rule you can greatly simplify it to

 $(Get-Content 'C:\Temp\regex_file\input.txt') -creplace "\\DE\s*$","\DE_02"  | out-file 'C:\Temp\regex_file\output.txt' -enc ascii

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Daniela.M replied on 09-17-2012 4:35 AM

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Thank you so much!!!

Works perfect =)

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nohandle replied on 09-17-2012 5:03 AM

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You're welcome :)

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Aleksandar replied on 09-17-2012 7:53 AM

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nohandle, you are brilliant!

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nohandle replied on 09-17-2012 8:03 AM

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Thanks :)