CMD or Powershell command to combine (merge) corresponding lines from two files

Question

Is it possible using CMD and Powershell to combine 2 files into 1 file like this:

file1-line1 tab file2-line1
file1-line2 tab file2-line2
file1-line3 tab file2-li         


        

Answer 1

A generalized solution supporting multiple files, building on Ansgar Wiechers' great, memory-efficient System.IO.StreamReader solution:

PowerShell's ability to invoke members (properties, methods) directly on a collection and have them automatically invoked on all items in the collection (member enumeration, v3+) allows for easy generalization:

# Make sure .NET has the same current dir. as PS.
[System.IO.Directory]::SetCurrentDirectory($PWD)

# The input file paths.
$files = 'file1', 'file2', 'file3'

# Create stream-reader objects for all input files.
$readers = [IO.StreamReader[]] $files

# Keep reading while at least 1 file still has more lines.
while ($readers.EndOfStream -contains $false) {

  # Read the next line from each stream (file).
  # Streams that are already at EOF fortunately just return "".
  $lines = $readers.ReadLine()

  # Output the lines separated with tabs.
  $lines -join "`t"

}

# Close the stream readers.
$readers.Close()

---

Get-MergedLines (source code below; invoke with -? for help) wraps the functionality in a function that:

• accepts a variable number of filenames - both as an argument and via the pipeline

• uses a configurable separator to join the lines (defaults to a tab)

• allows trimming trailing separator instances

function Get-MergedLines() {
<#
.SYNOPSIS
Merges lines from 2 or more files with a specifiable separator (default is tab).

.EXAMPLE
> Get-MergedLines file1, file2 '<->'

.EXAMPLE
> Get-ChildItem file? | Get-MergedLines
#>
  param(
    [Parameter(Mandatory, ValueFromPipeline, ValueFromPipelineByPropertyName)]
    [Alias('PSPath')]
    [string[]] $Path,

    [string] $Separator = "`t",

    [switch] $TrimTrailingSeparators
  )

  begin { $allPaths = @() }

  process { $allPaths += $Path }

  end {

    # Resolve all paths to full paths, which may include wildcard resolution.
    # Note: By using full paths, we needn't worry about .NET's current dir.
    #       potentially being different.
    $fullPaths = (Resolve-Path $allPaths).ProviderPath

    # Create stream-reader objects for all input files.
    $readers = [System.IO.StreamReader[]] $fullPaths

    # Keep reading while at least 1 file still has more lines.
    while ($readers.EndOfStream -contains $false) {

      # Read the next line from each stream (file).
      # Streams that are already at EOF fortunately just return "".
      $lines = $readers.ReadLine()

      # Join the lines.
      $mergedLine = $lines -join $Separator

      # Trim (remove) trailing separators, if requested.
      if ($TrimTrailingSeparators) {
        $mergedLine = $mergedLine -replace ('^(.*?)(?:' + [regex]::Escape($Separator) + ')+$'), '$1'
      }

      # Output the merged line.
      $mergedLine

    }

    # Close the stream readers.
    $readers.Close()

  }

}