CODEWITHSUNDEEP
powershelltext-filesline-numbers
BoomRamada
BoomRamada

Reputation: 141

How to extract specific line from text file

I got a large log file (user.log) , eg: 

   2019-10-02 00:03:55.407095
   2019-10-02 00:03:55.410345
   2019-10-02 00:03:55.410765
   2019-10-02 00:03:55.411187
   2019-10-02 00:03:55.411791
   2019-10-02 00:03:55.412657

How do I just extract the line number #3 from the log file as;

2019-10-02 00:03:55.410765

By using powershell script?

Upvotes: 5

Views: 18753

Answers (2)

mklement0
mklement0

Reputation: 437823

A simple and memory-efficient approach suitable for processing large input files is to combine Get-Content with Select-Object:

Get-Content user.log | Select-Object -Skip 2 -First 1

  • -Skip 2 instructs Select-Object to skip the first 2 input lines output by Get-Content.

  • Therefore, it is the 3rd line that is the first processed - and output - by Select-Object, and
    -First 1 makes it stop processing right afterwards, so that the rest of the file needn't be read.

A faster approach, IF the portion of the file up to the desired line number is small enough to fit into memory as a whole:

(Get-Content -TotalCount 3 -ReadCount -3 user.log)[-1]

  • -TotalCount 3 tells Get-Content to read 3 lines (at most) in total.

    • -ReadCount 3 additionally tells Get-Content to read all 3 lines at once into an array and send it through the pipeline as a single object - rather than line by line - this isn't necessary, but speeds up the command.

  • [-1] then extracts the last element from the resulting array, which is the 3rd line.

If the input file as a whole is small, the following solution is simplest:

(Get-Content user.log)[2]  # add -ReadCount 0 to speed things up

That is, Get-Content reads all lines, which (...) collects in an array in memory, and [2] accesses the array's 3rd element, i.e., the 3rd line.

A simple way of speeding up this solution would be to add -ReadCount 0, which makes Get-Content emit the array of all input lines itself, as a single output object, as opposed to emitting lines one by one and letting (...) collect them in an array afterwards.

Upvotes: 11

xyz
xyz

Reputation: 403

You could try this and change the $target variable to whatever line you want to extract:

$content = Get-Content "path to user.log"
$count = 0
$target = 3

foreach ($line in $content) {
    $count += 1
    if ($count -eq $target) {
        $line
        break
    }
}

Upvotes: 0

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