CODEWITHSUNDEEP
powershell
Jonny Cundall
Jonny Cundall

Reputation: 2612

Get the first n characters of a large file with PowerShell

I've got a huge XML file (0.5 GB), with no line breaks. I want to be able to look at, say, the first 200 characters without opening the whole file. Is there a way to do this with PowerShell?

Upvotes: 11

Views: 23423

Answers (5)

Pygar
Pygar

Reputation: 1

(get-content myfile).Substring(0,x)

Where x is the number of characters you want from each line e.g. $lines = (get-content myfile).Substring(0,10) will return an array of strings where each member of the array contains the first 10 characters of each line in myfile.

Upvotes: -2

Kevin Scharnhorst
Kevin Scharnhorst

Reputation: 887

@keith-hill got me most of the way there.

Here's what I used to get the first character out of a VMware Virtual Disk. There is important information in the first 1000 or so characters, but I'd never get at it trying to open a 30GB file.

$bytes = Get-Content .\VMwareVirtualDiskFile.vmdk -Encoding byte -TotalCount 1000
[String]::Concat([char[]]($bytes))

Upvotes: 0

Zimba
Zimba

Reputation: 3673

Copying binary files via powershell commandlets tend to be a bit slow. You may, however, run the following commands from powershell to get a decent performance:

cmd /c copy /b "large file.ext" "first n.ext"
FSUTIL file seteof "first n.ext" $nbytes

Tested in Win 10 PS 5.1
Result: 1.43GB processed in 4 seconds

Upvotes: 2

Keith Hill
Keith Hill

Reputation: 201602

PowerShell Desktop (up to 5.1)

You can read at the byte level with Get-Content like so:

$bytes = Get-Content .\files.txt -Encoding byte -TotalCount 200
[System.Text.Encoding]::Unicode.GetString($bytes)

If the log file is ASCII you can simplify this to:

[char[]](Get-Content .\files.txt -Encoding byte -TotalCount 200)

PowerShell Core 6.0 and newer

PowerShell Core doesn't support byte encoding. It's been replaced by -AsByteStream parameter.

$bytes = Get-Content .\file.txt -AsByteStream -TotalCount 200
[System.Text.Encoding]::Unicode.GetString($bytes)

Upvotes: 30

Eris
Eris

Reputation: 7638

Get-Content takes a -ReadCount option so you can take only the first X lines.

If you really want character granularity, you'll need to use one of the [IO.File]::Read methods from .NET

Upvotes: 0

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