Remove Top Line of Text File with PowerShell - powershell

Question

I am trying to just remove the first line of about 5000 text files before importing them.
I am still very new to PowerShell so not sure what to search for or how to approach this. My current concept using pseudo-code:
set-content file (get-content unless line contains amount)
However, I can't seem to figure out how to do something like contains.

Answer 1

While I really admire the answer from #hoge both for a very concise technique and a wrapper function to generalize it and I encourage upvotes for it, I am compelled to comment on the other two answers that use temp files (it gnaws at me like fingernails on a chalkboard!).
Assuming the file is not huge, you can force the pipeline to operate in discrete sections--thereby obviating the need for a temp file--with judicious use of parentheses:
(Get-Content $file | Select-Object -Skip 1) | Set-Content $file
... or in short form:
(gc $file | select -Skip 1) | sc $file

Answer 2

It is not the most efficient in the world, but this should work:
get-content $file |
select -Skip 1 |
set-content "$file-temp"
move "$file-temp" $file -Force

Answer 3

Using variable notation, you can do it without a temporary file:
${C:\file.txt} = ${C:\file.txt} | select -skip 1
function Remove-Topline ( [string[]]$path, [int]$skip=1 ) {
if ( -not (Test-Path $path -PathType Leaf) ) {
throw "invalid filename"
}
ls $path |
% { iex "`${$($_.fullname)} = `${$($_.fullname)} | select -skip $skip" }
}

Answer 4

I just had to do the same task, and gc | select ... | sc took over 4 GB of RAM on my machine while reading a 1.6 GB file. It didn't finish for at least 20 minutes after reading the whole file in (as reported by Read Bytes in Process Explorer), at which point I had to kill it.
My solution was to use a more .NET approach: StreamReader + StreamWriter.
See this answer for a great answer discussing the perf: In Powershell, what's the most efficient way to split a large text file by record type?
Below is my solution. Yes, it uses a temporary file, but in my case, it didn't matter (it was a freaking huge SQL table creation and insert statements file):
PS> (measure-command{
$i = 0
$ins = New-Object System.IO.StreamReader "in/file/pa.th"
$outs = New-Object System.IO.StreamWriter "out/file/pa.th"
while( !$ins.EndOfStream ) {
$line = $ins.ReadLine();
if( $i -ne 0 ) {
$outs.WriteLine($line);
}
$i = $i+1;
}
$outs.Close();
$ins.Close();
}).TotalSeconds
It returned:
188.1224443

Answer 5

Inspired by AASoft's answer, I went out to improve it a bit more:
Avoid the loop variable $i and the comparison with 0 in every loop
Wrap the execution into a try..finally block to always close the files in use
Make the solution work for an arbitrary number of lines to remove from the beginning of the file
Use a variable $p to reference the current directory
These changes lead to the following code:
$p = (Get-Location).Path
(Measure-Command {
# Number of lines to skip
$skip = 1
$ins = New-Object System.IO.StreamReader ($p + "\test.log")
$outs = New-Object System.IO.StreamWriter ($p + "\test-1.log")
try {
# Skip the first N lines, but allow for fewer than N, as well
for( $s = 1; $s -le $skip -and !$ins.EndOfStream; $s++ ) {
$ins.ReadLine()
}
while( !$ins.EndOfStream ) {
$outs.WriteLine( $ins.ReadLine() )
}
}
finally {
$outs.Close()
$ins.Close()
}
}).TotalSeconds
The first change brought the processing time for my 60 MB file down from 5.3s to 4s. The rest of the changes is more cosmetic.

Answer 6

$x = get-content $file
$x[1..$x.count] | set-content $file
Just that much. Long boring explanation follows. Get-content returns an array. We can "index into" array variables, as demonstrated in this and other Scripting Guys posts.
For example, if we define an array variable like this,
$array = #("first item","second item","third item")
so $array returns
first item
second item
third item
then we can "index into" that array to retrieve only its 1st element
$array[0]
or only its 2nd
$array[1]
or a range of index values from the 2nd through the last.
$array[1..$array.count]

Answer 7

I just learned from a website:
Get-ChildItem *.txt | ForEach-Object { (get-Content $_) | Where-Object {(1) -notcontains $_.ReadCount } | Set-Content -path $_ }
Or you can use the aliases to make it short, like:
gci *.txt | % { (gc $_) | ? { (1) -notcontains $_.ReadCount } | sc -path $_ }

Answer 8

Another approach to remove the first line from file, using multiple assignment technique. Refer Link
$firstLine, $restOfDocument = Get-Content -Path $filename
$modifiedContent = $restOfDocument
$modifiedContent | Out-String | Set-Content $filename

Answer 9

skip` didn't work, so my workaround is
$LinesCount = $(get-content $file).Count
get-content $file |
select -Last $($LinesCount-1) |
set-content "$file-temp"
move "$file-temp" $file -Force

Answer 10

Following on from Michael Soren's answer.
If you want to edit all .txt files in the current directory and remove the first line from each.
Get-ChildItem (Get-Location).Path -Filter *.txt |
Foreach-Object {
(Get-Content $_.FullName | Select-Object -Skip 1) | Set-Content $_.FullName
}

Answer 11

For smaller files you could use this:
& C:\windows\system32\more +1 oldfile.csv > newfile.csv | out-null
... but it's not very effective at processing my example file of 16MB. It doesn't seem to terminate and release the lock on newfile.csv.