Powershell write array using StreamWriter

Question

I'm new to PowerShell and am trying to write a script that will allow me to read through a very large text file and extract certain lines if they begin with "2020".

When a match is found, it should write to an array ($Lines), then I'm trying to output this filtered content to another text file using StreamWriter.

Here is what I have so far:

$reader = New-Object System.IO.StreamReader 'C:\Users\PSTest\Years.txt'
$writer = New-Object System.IO.StreamWriter 'C:\Users\PSTest\Data.txt'

$lines = @()

        Foreach ($line in $reader) {

             if ($reader -ne $null) {
             while (!$reader.EndOfStream) {
             $line = $reader.ReadLine()

                   if ($line.StartsWith("2020")) { 
                   $lines += $line }

                         $writer.writeline($lines) }      
    }
  }  

 $reader.dispose()
 $writer.dispose()

When I write to the console I can tell there are hundreds of matches, but nothing ever gets written to the output file (Data.txt).

What am I missing? Thank you in advance.

Doug Maurer · Accepted Answer · 2021-04-15 17:30:08Z

2

You don't need to do all the collection operations.

$reader = New-Object System.IO.StreamReader 'C:\temp\Years.txt'
$writer = New-Object System.IO.StreamWriter 'C:\temp\Data.txt'

while($line = $reader.ReadLine()){
    if($line.StartsWith("2020")){
        $writer.WriteLine($line)
    }
}

$reader.Close()
$reader.Dispose()

$writer.Close()
$writer.Dispose()

I'd also suggest you look into using a switch statement.

Set-Content -Path 'C:\temp\Data.txt' -Value ($(
    switch -Regex -File C:\temp\years.txt {
        '^2020' {$_}
    }
))

answered Apr 15, 2021 at 17:30

Doug Maurer

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Comments

Esperento57 · Accepted Answer · 2021-04-15 17:21:59Z

0

if you want really use an array try this :

try
{
$reader = New-Object System.IO.StreamReader 'C:\temp\test.txt'
$lines = @()

while (($line = $reader.ReadLine()) -ne $null)  
{  
if ($line.StartsWith("2020")) { $lines += $line }
}

#not necessary to keep file open
$reader.Close() 

$writer = New-Object System.IO.StreamWriter 'C:\temp\test2.txt'
$lines | %{$writer.WriteLine($_)}

}
finally
{

    if ($reader -ne $null)
    {
        $reader.Close()
        $reader.Dispose()
    }

    if ($writer -ne $null)
    {
        $writer.Close()
        $writer.Dispose()
    }
}

otherwise :

try
{
$reader = New-Object System.IO.StreamReader 'C:\temp\test.txt'
$writer = New-Object System.IO.StreamWriter 'C:\temp\test2.txt'

while (($line = $reader.ReadLine()) -ne $null)  
{  
if ($line.StartsWith("2020")) { $writer.WriteLine($line)}
}

}
finally
{

    if ($reader -ne $null)
    {
        $reader.Close()
        $reader.Dispose()
    }

    if ($writer -ne $null)
    {
        $writer.Close()
        $writer.Dispose()
    }
}

answered Apr 15, 2021 at 17:21

Esperento57

17.6k6 gold badges42 silver badges47 bronze badges

1 Comment

Chester205 Over a year ago

Thank you so much Doug and Esperento! You both solved my problem.

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