How to change values in text files? - regex

Question

I am simply trying to create a powershell script that will change number values in a set of text files. The data in the text files are separated by semi-colons. The values I want to change are always the 2nd and 3rd tokens on each line of the text file.
An example of a line in one of the files:
"Bridge_Asphalt_F";202498.396728;1104.362183;9.721280;0.000000;0.000000;1.000000;-1.299559;
I want to allow the user of the script to enter values to be added to(or subtracted from) the 2nd and 3rd values in all the lines of all the text files in the current directory.
I have a very basic understanding of scripting, but I've been searching around for hours trying to wrap my head around how this would be accomplished.
This is what I have so far but I'm sure I'm getting a few things wrong:
$east = Read-Host 'Easting?'
$north = Read-Host 'Northing?'
Get-ChildItem *.txt |
Foreach-Object {
$c = ($_ | Get-Content)
$c = $c -replace $regexB,$regexB+$east
$c = $c -replace $regexC,$regexC+$north
[IO.File]::WriteAllText($_.FullName, ($c -join "`r`n"))
}
The values determine an object's location on a map (for a game) and I want to be able to move all objects on the entire map by a certain distance on both x and y axis.

Answer 1

Assuming that each line in the file has the same format as your example, then you can treat the file as a CSV and update it like this:
$offset2 = 100
$offset3 = 100
Import-Csv .\data.txt -Delimiter ';' -Header (1 .. 9) |
ForEach-Object {
$_.2 = ([double]$_.2) + $offset2
$_.3 = ([double]$_.3) + $offset3
$_
} | ConvertTo-Csv -NoTypeInformation -Delimiter ';' |
Select-Object -Skip 1 |
Add-Content .\updated.txt
Note:
ConvertTo-Csv surrounds each item with quotes, so you end up with something like this:
"Bridge_Asphalt_F";"202198.396728";"1104.362183";"9.721280";"0.000000";"0.000000";"1.000000";"-1.299559"
This may cause problems if this isn't expected by your game. If so, then some more processing on the pipeline could be done to strip it out.
Also, I've had issues in the past with trying to import and export to the same CSV file, hence my code outputs to a different file. Test it yourself and if it works with the same file, great, otherwise, copy my example, then add a line to replace the existing file with the new one (e.g. using Move-Item).

Answer 2

I guess that's what you need:
cls
cd C:\Users\dandraka\Desktop\test #or whereever
$eastStr = Read-Host 'Easting?'
$northStr = Read-Host 'Northing?'
# convert input to number
$east = [decimal]::Parse($eastStr)
$north = [decimal]::Parse($northStr)
# loop through files
$files = Get-ChildItem *.txt
$files | Foreach-Object {
$fileName = $_.FullName # just for clarity
Write-Host $fileName
$newLines = New-Object System.Collections.ArrayList
# loop through lines of each file
$lines = Get-Content -Path $fileName
$lines | ForEach-Object {
$line = $_.ToString() # just for clarity
$lineItems = $line -split ';'
$pointName = $lineItems[0]
$latitudeStr = $lineItems[1]
$longitudeStr = $lineItems[2]
# convert to number
$latitude = [decimal]::Parse($latitudeStr)
$longitude = [decimal]::Parse($longitudeStr)
Write-Host "$pointName latitude $latitude , longitude $longitude"
# do the math
$newLatitude = $latitude + $north
$newLongitude = $longitude + $east
Write-Host "$pointName new latitude $newLatitude , new longitude $newLongitude"
# recontruct the line
$newLine = ""
for($i=0; $i -lt $lineItems.Count; $i++) {
if ($i -eq 1) {
$newLine += "$newLatitude;"
continue
}
if ($i -eq 2) {
$newLine += "$newLongitude;"
continue
}
# this if fixes a small bug, without it there are two ; at the end of each line
if ($lineItems[$i].Length -gt 0) {
$newLine += "$($lineItems[$i]);"
}
}
Write-Host "Old line $line"
Write-Host "New line $newLine"
$newLines.Add($newLine) | Out-Null
}
# write file
$newFilename = $fileName.Replace(".txt", ".dat")
[System.IO.File]::WriteAllLines($newFilename, $newLines)
Write-Host "File $newFilename written"
}
A few things to note here:
As you mention that you're starting with powershell, I've written the code more verbose than I would for, say, a seasoned developer. But that actually doesn't hurt.
For the same reason, the code is sub-optimal on purpose (makes for easier to read code). But for better performance and large files (say, a few 10s of MB or more) you need to do things differently, e.g. avoid strings and use string builder instead.
Obviously you can comment out all the Write-Host statements, they're there just to help you make sure the code is working properly.
Hope that helps!
Jim

Answer 3

If your game cannot handle the quoted coordinate values you get when using ConvertTo-Csv or Export-Csv, this should update the values while leaving the quotes off:
$eastOffset = 100
$northOffset = -200
(Get-Content 'D:\coordinates.txt') | ForEach-Object {
$fields = $_ -split ';'
[double]$fields[1] += $eastOffset
[double]$fields[2] += $northOffset
# write the updated stuff to file
Add-Content -Path 'D:\newcoordinates.txt' -Value ($fields -join ';')
}
this content
"Bridge_Asphalt_F";202498.396728;1104.362183;9.721280;0.000000;0.000000;1.000000;-1.299559;
"Road_Asphalt_F";202123.396728;1104.362456;9.721280;0.000000;0.000000;1.000000;-1.299559;
would become
"Bridge_Asphalt_F";202598.396728;904.362183;9.721280;0.000000;0.000000;1.000000;-1.299559;
"Road_Asphalt_F";202223.396728;904.362456;9.721280;0.000000;0.000000;1.000000;-1.299559;