PowerShell function that colors portions of the default host output that match given patterns.

Out-HostColored.ps1

<#

  Prerequisites: PowerShell version 2 or above.
  License: MIT
  Author:  Michael Klement <[email protected]>

  DOWNLOAD, from PowerShell version 3 or above:

    irm https://gist.github.com/mklement0/243ea8297e7db0e1c03a67ce4b1e765d/raw/Out-HostColored.ps1 | iex

  The above directly defines the function below in your session and offers guidance for making it available in future 
  sessions too.
  
  Alternatively, download this file manually and dot-source it (e.g.: . /Out-HostColored.ps1)

  To learn what the function does:
    * see the next comment block
    * or, once downloaded, invoke the function with -? or pass its name to Get-Help.
 
#>

Function Out-HostColored {
<#
.SYNOPSIS
Colors portions of the default host output that match given patterns.

.DESCRIPTION
Colors portions of the default-formatted host output based on either
regular expressions or literal substrings, assuming the host is a console or
supports colored output using console colors.

Matching is restricted to a single line at a time, but coloring multiple
matches on a given line is supported.

Two basic syntax forms are supported:

  * Single-color, via -Pattern, -ForegroundColor and -BackgroundColor

  * Multi-color (color per pattern), via a hashtable (dictionary) passed to
    -PatternColorMap.

Note: Since output is sent to the host rather than the pipeline, you cannot
      chain calls to this function.

.PARAMETER Pattern
One or more search patterns specifying what parts of the formatted 
representations of the input objects should be colored.

 * By default, these patterns are interpreted as regular expressions.

 * If -SimpleMatch is also specified, the patterns are interpreted as literal
   substrings.

.PARAMETER ForegroundColor
The foreground color to use for the matching portions.
Defaults to yellow.

.PARAMETER BackgroundColor
The optional background color to use for the matching portions.

.PARAMETER PatternColorMap
A hashtable (dictionary) with one or more entries in the following format:

  <pattern-or-pattern-array> = <color-spec>

<pattern-or-pattern-array> is either a single string or an array of strings
specifying the regex pattern(s) or literal substring(s) (with -SimpleMatch)
to match.

NOTE: If you're specifying an array literally, you must enclose it in (...) or
      @(...), and the individual patterns must all be quoted; e.g.:
        @('foo', 'bar')

<color-spec> is a string that contains either a foreground [ConsoleColor] 
color alone (e.g. 'red'), a combination with a background color separated by ","
(e.g., 'red,white') or just a background color (e.g, ',white').

NOTE: If *multiple* patterns stored in a given hashtable may match on a given
      line and you want the *first* matching pattern to "win" predictably, be
      sure to pass an [ordered] hashtable ([ordered] @{ Foo = 'red; ... })

See the examples for a complete example.

.PARAMETER CaseSensitive
Matches the patterns case-sensitively.
By default, matching is case-insensitive.

.PARAMETER WholeLine
Specifies that the entire line containing a match should be colored,
not just the matching portion.

.PARAMETER SimpleMatch
Interprets the -Pattern argument(s) as a literal substrings to match rather
than as regular expressions.

.PARAMETER InputObject
The input object(s) whose formatted representations to color selectively.
Typically provided via the pipeline.

.EXAMPLE
'A fool and his money', 'foo bar' | Out-HostColored foo

Prints the substring 'foo' in yellow in the two resulting output lines.

.EXAMPLE
Get-Date | Out-HostColored '\p{L}+' red white

Outputs the current date with all tokens composed of letters (p{L}) only in red
on a white background.

.EXAMPLE
Get-Date | Out-HostColored @{ '\p{L}+' = 'red,white' }

Same as the previous example, only via the dictionary-based -PatternColorMap
parameter (implied).

.EXAMPLE
'It ain''t easy being green.' | Out-HostColored @{ ('easy', 'green') = 'green'; '\bbe.+?\b' = 'black,yellow' }

Prints the words 'easy' and 'green' in green, and the word 'being' in black on yellow.
Note the need to enclose pattern array 'easy', 'green' in (...), which also necessitates
quoting its element.

.EXAMPLE
Get-ChildItem | select Name | Out-HostColored -WholeLine -SimpleMatch .txt

Highlight all text file names in green.

.EXAMPLE
'apples', 'kiwi', 'pears' | Out-HostColored '^a', 's$' blue

Highlight all "A"s at the beginning and "S"s at the end of lines in blue.
#>

  # === IMPORTANT:
  #   * At least for now, we remain PSv2-COMPATIBLE.
  #   * Thus: 
  #     * no `[ordered]`, `::new()`, `[pscustomobject]`, ...
  #     * No implicit Boolean properties in [CmdletBinding()] and [Parameter()] attributes (`Mandatory = $true` instead of just `Mandatory`)
  # ===

  [CmdletBinding(DefaultParameterSetName = 'SingleColor')]
  param(
    [Parameter(ParameterSetName = 'SingleColor', Position = 0, Mandatory = $True)] [string[]] $Pattern,
    [Parameter(ParameterSetName = 'SingleColor', Position = 1)] [ConsoleColor] $ForegroundColor = [ConsoleColor]::Yellow,
    [Parameter(ParameterSetName = 'SingleColor', Position = 2)] [ConsoleColor] $BackgroundColor,
    [Parameter(ParameterSetName = 'PerPatternColor', Position = 0, Mandatory = $True)] [System.Collections.IDictionary] $PatternColorMap,
    [Parameter(ValueFromPipeline = $True)] $InputObject,
    [switch] $WholeLine,
    [switch] $SimpleMatch,
    [switch] $CaseSensitive
  )

  begin {

    Set-StrictMode -Version 1

    if ($PSCmdlet.ParameterSetName -eq 'SingleColor') {

      # Translate the indiv. arguments into the dictionary format suppoorted
      # by -PatternColorMap, so we can process $PatternColorMap uniformly below.
      $PatternColorMap = @{
        $Pattern = $ForegroundColor, $BackgroundColor
      }

    } 
    # Otherwise: $PSCmdlet.ParameterSetName -eq 'PerPatternColor', i.e. a dictionary
    #            mapping patterns to colors was direclty passed in $PatternColorMap

    try {

      # The options for the [regex] instances to create.
      # We precompile them for better performance with many input objects.
      [System.Text.RegularExpressions.RegexOptions] $reOpts = 
      if ($CaseSensitive) { 'Compiled, ExplicitCapture' } 
      else { 'Compiled, ExplicitCapture, IgnoreCase' }

      # Transform the dictionary:
      #  * Keys: Consolidate multiple patterns into a single one with alternation and
      #          construct a [regex] instance from it.
      #  * Values: Transform the "[foregroundColor],[backgroundColor]" strings into an arguments
      #            hashtable that can be used for splatting with Write-Host.
      $map = [ordered] @{ } # !! For stable results in repeated enumerations, use [ordered].
                            # !! This matters when multiple patterns match on a given line, and also requires the
                            # !! *caller* to pass an [ordered] hashtable to -PatternColorMap
      foreach ($entry in $PatternColorMap.GetEnumerator()) {

        # Create a Write-Host color-arguments hashtable for splatting.
        if ($entry.Value -is [array]) {
          $fg, $bg = $entry.Value # [ConsoleColor[]], from the $PSCmdlet.ParameterSetName -eq 'SingleColor' case.
        }
        else {
          $fg, $bg = $entry.Value -split ','
        }
        $colorArgs = @{ }
        if ($fg) { $colorArgs['ForegroundColor'] = [ConsoleColor] $fg }
        if ($bg) { $colorArgs['BackgroundColor'] = [ConsoleColor] $bg }

        # Consolidate the patterns into a single pattern with alternation ('|'),
        # escape the patterns if -SimpleMatch was passsed.
        $re = New-Object regex -Args `
          $(if ($SimpleMatch) {
              ($entry.Key | ForEach-Object { [regex]::Escape($_) }) -join '|'
            } 
            else { 
              ($entry.Key | ForEach-Object { '({0})' -f $_ }) -join '|'
            }),
          $reOpts

        # Add the tansformed entry.
        $map[$re] = $colorArgs

      }
    } 
    catch { throw }

    # Construct the arguments to pass to Out-String.
    $htArgs = @{ Stream = $True }
    if ($PSBoundParameters.ContainsKey('InputObject')) { # !! Do not use `$null -eq $InputObject`, because PSv2 doesn't create this variable if the parameter wasn't bound.
      $htArgs.InputObject = $InputObject
    }

    # Construct the script block that is used in the steppable pipeline created
    # further below.
    $scriptCmd = {

      # Format the input objects with Out-String and output the results line
      # by line, then look for matches and color them.
      & $ExecutionContext.InvokeCommand.GetCommand('Microsoft.PowerShell.Utility\Out-String', 'Cmdlet') @htArgs | ForEach-Object {

        # Match the input line against all regexes and collect the results.
        $matchInfos = :patternLoop foreach ($entry in $map.GetEnumerator()) {
          foreach ($m in $entry.Key.Matches($_)) {
            @{ Index = $m.Index; Text = $m.Value; ColorArgs = $entry.Value }
            if ($WholeLine) { break patternLoop }
          }
        }
        
        # # Activate this for debugging.
        # $matchInfos | Sort-Object { $_.Index } | Out-String | Write-Verbose -vb
      
        if (-not $matchInfos) {
          # No match found - output uncolored.
          Write-Host -NoNewline $_
        }
        elseif ($WholeLine) {
          # Whole line should be colored: Use the first match's color
          $colorArgs = $matchInfos.ColorArgs
          Write-Host -NoNewline @colorArgs $_
        }
        else {
          # Parts of the line must be colored:
          # Process the matches in ascending order of start position.    
          $offset = 0
          foreach ($mi in $matchInfos | Sort-Object { $_.Index }) { # !! Use of a script-block parameter is REQUIRED in WinPSv5.1-, because hashtable entries cannot be referred to like properties, unlinke in PSv7+
            if ($mi.Index -lt $offset) {
              # Ignore subsequent matches that overlap with previous ones whose colored output was already produced.
              continue 
            }
            elseif ($offset -lt $mi.Index) {
              # Output the part *before* the match uncolored.
              Write-Host -NoNewline $_.Substring($offset, $mi.Index - $offset)
            }
            $offset = $mi.Index + $mi.Text.Length
            # Output the match at hand colored.
            $colorArgs = $mi.ColorArgs
            Write-Host -NoNewline @colorArgs $mi.Text
          }
          # Print any remaining part of the line uncolored.
          if ($offset -lt $_.Length) {
            Write-Host -NoNewline $_.Substring($offset)
          }
        }
        Write-Host '' # Terminate the current output line with a newline - this also serves to reset the console's colors on Unix.

      }
    }

    # Create the script block as a *steppable pipeline*, which enables
    # to perform regular streaming pipeline processing, without having to collect
    # everything in memory first.
    $steppablePipeline = $scriptCmd.GetSteppablePipeline($myInvocation.CommandOrigin)
    $steppablePipeline.Begin($PSCmdlet)

  } # begin

  process
  {
    $steppablePipeline.Process($_)
  }

  end
  {
    $steppablePipeline.End()
  }

}


# --------------------------------
# GENERIC INSTALLATION HELPER CODE
# --------------------------------
#    Provides guidance for making the function persistently available when
#    this script is either directly invoked from the originating Gist or
#    dot-sourced after download.
#    IMPORTANT: 
#       * DO NOT USE `exit` in the code below, because it would exit
#         the calling shell when Invoke-Expression is used to directly
#         execute this script's content from GitHub.
#       * Because the typical invocation is DOT-SOURCED (via Invoke-Expression), 
#         do not define variables or alter the session state via Set-StrictMode, ...
#         *except in child scopes*, via & { ... }
if ($MyInvocation.Line -eq '') {
  # Most likely, this code is being executed via Invoke-Expression directly 
  # from gist.github.com

  # To simulate for testing with a local script, use the following:
  # Note: Be sure to use a path and to use "/" as the separator.
  #  iex (Get-Content -Raw ./script.ps1)

  # Derive the function name from the invocation command, via the enclosing
  # script name presumed to be contained in the URL.
  # NOTE: Unfortunately, when invoked via Invoke-Expression, $MyInvocation.MyCommand.ScriptBlock
  #       with the actual script content is NOT available, so we cannot extract
  #       the function name this way.
  & {
    
    param($invocationCmdLine)
    
    # Try to extract the function name from the URL.
    $funcName = $invocationCmdLine -replace '^.+/(.+?)(?:\.ps1).*$', '$1'
    if ($funcName -eq $invocationCmdLine) {
      # Function name could not be extracted, just provide a generic message.
      # Note: Hypothetically, we could try to extract the Gist ID from the URL
      #       and use the REST API to determine the first filename.
      Write-Verbose -Verbose "Function is now defined in this session."
    } 
    else {

      # Indicate that the function is now defined and also show how to
      # add it to the $PROFILE or convert it to a script file.
      Write-Verbose -Verbose @"
Function `"$funcName`" is now defined in this session.

* If you want to add this function to your `$PROFILE, run the following:

   "``nfunction $funcName {``n`${function:$funcName}``n}" | Add-Content `$PROFILE

* If you want to convert this function into a script file that you can invoke
  directly, run:

   "`${function:$funcName}" | Set-Content $funcName.ps1 -Encoding $('utf8' + ('', 'bom')[[bool] (Get-Variable -ErrorAction Ignore IsCoreCLR -ValueOnly)])

"@
    }

  } $MyInvocation.MyCommand.Definition # Pass the original invocation command line to the script block.

}
else {
  # Invocation presumably as a local file after manual download, 
  # either dot-sourced (as it should be) or mistakenly directly.  

  & {
    param($originalInvocation)

    # Parse this file to reliably extract the name of the embedded function, 
    # irrespective of the name of the script file.
    $ast = $originalInvocation.MyCommand.ScriptBlock.Ast
    $funcName = $ast.Find( { $args[0] -is [System.Management.Automation.Language.FunctionDefinitionAst] }, $false).Name

    if ($originalInvocation.InvocationName -eq '.') {
      # Being dot-sourced as a file.
      
      # Provide a hint that the function is now loaded and provide
      # guidance for how to add it to the $PROFILE.
      Write-Verbose -Verbose @"
Function `"$funcName`" is now defined in this session.

If you want to add this function to your `$PROFILE, run the following:

    "``nfunction $funcName {``n`${function:$funcName}``n}" | Add-Content `$PROFILE

"@

    }
    else {
      # Mistakenly directly invoked.

      # Issue a warning that the function definition didn't effect and
      # provide guidance for reinvocation and adding to the $PROFILE.
      Write-Warning @"
This script contains a definition for function "$funcName", but this definition
only takes effect if you dot-source this script.

To define this function for the current session, run:
  
  . "$($originalInvocation.MyCommand.Path)"
  
"@
    } 

  }  $MyInvocation # Pass the original invocation info to the helper script block.

}