How do you count consecutive strings in file using powershell?

PowerShell's equivalent to the uniq utility, the Get-Unique cmdlet, unfortunately has no equivalent to the former's -c option for prepending the number of consecutive duplicate lines (as of PowerShell v6.2).

^{Note: Enhancing Get-Unique to support a -c-like feature and other features offered by the uniq POSIX utility is the subject of this feature request on GitHub.}

Therefore, you must roll your own solution:

function Get-UniqueWithCount {

  begin {
    $instanceCount = 1; $prevLine = $null
  }

  process {
    if ($_ -eq $prevLine) {
      ++$instanceCount
    } elseif ($null -ne $prevLine) {
      [pscustomobject] @{ InstanceCount = $instanceCount; Line = $prevLine }
      $instanceCount = 1
    }
    $prevLine = $_
  }

  end {
    [pscustomobject] @{ InstanceCount = $instanceCount; Line = $prevLine }
  }

}

The above function accepts input from the pipeline (object by object as $_ in the process { ... } block). It compares each object (line) to the previous one and, if they're equal, increments the instance count; once a different line is found, the previous line is output, along with its instance count, as an object with properties InstanceCount and Line. The end { ... } block outputs the final output object for the last block of identical consecutive lines. See about_Functions_Advanced.

Then invoke it as follows:

Get-Content fule | Get-UniqueWithCount

which yields:

InstanceCount Line
------------- ----
            3 1
            4 0
            3 1
            1 0
            2 1
            3 0
            1 1
            1 0
            3 1
            2 0

Since Get-UniqueWithCount conveniently outputs objects whose typed properties we can act on, the equivalent of sort -hr (sort by embedded numbers (-h), in descending (reverse) order (-r)) is easy:

Get-Content fule | Get-UniqueWithCount | Sort-Object -Descending InstanceCount

which yields:

InstanceCount Line
------------- ----
            4 0
            3 1
            3 1
            3 0
            3 1
            2 1
            2 0
            1 0
            1 1
            1 0