SingleInstanceAccumulator

Purpose

See typical stack-o's expressing the need, e.g. this one.

The gist is it comes in handy as a bridge between selecting multiple files or folders in custom Windows File Explorer context menus and sending all the selections to various scripts or 3rd party tools.

Usage

"-c:command line" (default: cmd /c echo $files && pause)
  $files will be replace with aggregated list

-f = output each item on separate line to new tempfile
  $files will be replaced by the tempfile path
  quote will default to nothing

-d:delimiter (default: ,)
-q:quote character around each accumulated argument (default: ") - see examples below
-t:timeout millisecs (default: 200)
-w = hidden launch (hides console window for cmd.exe & powershell.exe)
-v = debug output

Command Line Examples

Heads up about registry entries:

my primary interest and therefore these docs focus on adding custom context menus to File Explorer, which happens via registry entries under HKEY_CURRENT_USER\Software\Classes
registry entries like HKEY_CURRENT_USER\Software\Classes\*\shell\xxxx\command require full path on the main executable (e.g. c:\bin\SingleInstanceAccumulator.exe, not just SingleInstanceAccumulator.exe)... for some ungawdly reason of Windows, our path environment variable is not honored.
however the -c:command executed from SingleInstanceAccumulator will know your environment's path.
reg entries like HKEY_CURRENT_USER\Software\Classes\*\shell\ will map to all file types (via the asterisk "*"), which avoids needing to create an entry for each individual file type if you don't need it filetype specific.
otherwise replace the asterisk in item above with a specific filetype ... this gets into more esoterics than i care to elaborate on here =) looking at your existing shell entries is helpful and there is tons of writeups out there

examples are all formatted to be executed from WITHIN A BATCH FILE

as you get into the context menu game, you'll pile up a few you want to have at the ready to set up a new workstation, etc... so plan to save these in xyz_setup.cmd batch files to conveniently deploy to new windows environments
batch file context (versus interactive cmd.exe) requires doubling up environment variables %%'s to escape them
quotes also often need to be escaped depending on the layers of interpretation happening
and we need to double escape the "&" and "|" characters with "^" for the accumulated command line portion
- once to avoid the initial setup batch file from interpreting them directly
- and secondly to avoid the command line launched from SingleInstanceAccumulator from processing them
- ... so they are eventually present to be run directly from the final cmd.exe
if you're wanting to trial with interactive cmd.exe, the first layer of escapes would need to be removed

example 0 - feed files to a 3rd party exe

reg add "HKEY_CURRENT_USER\Software\Classes\*\shell\MyCommand\command" /f /ve /t REG_EXPAND_SZ /d "\"^%%bin^%%\SingleInstanceAccumulator\" -w \"-c:myprogram.exe $files\" \"%%1\""

example 1 - put selected files onto clipboard

this is a fun use of delimiter to create multiple echo statements that are then piped to "clip" device
note using the delimeter to add echo commands to each selected file as interesting leverage of native batch file capabilities

reg add "HKEY_CURRENT_USER\Software\Classes\*\shell\Path2Clip\command" /f /ve /t REG_EXPAND_SZ /d "\"^%%bin^%%\SingleInstanceAccumulator\" -w -d:\" ^^^& echo \" \"-c:cmd /c (echo $files) ^^^| clip\" \"%%1\""

when run from windows explorer context menu the above reg entry will execute a command line that looks like this:

"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" -ExecutionPolicy bypass C:\bin\transcode.ps1 -listFilePath 'C:\Users\Beej\AppData\Local\Temp\tmp5EEF.tmp'

example 2 - PowerShell script - using temp file approach

note: -f usage

reg add "HKEY_CURRENT_USER\Software\Classes\*\shell\MyCommand\command" /f /ve /t REG_EXPAND_SZ /d "\"^%%bin^%%\SingleInstanceAccumulator\" -w -f \"-c:powershell -ExecutionPolicy bypass \"^%%bin^%%\test.ps1 -listFilePath '$files'\" \"%%1\""

note: -listFilePath command line argument corresponds to test.ps1's $listFilePath param shown next below

corresponding test.ps1 sample:

param(
  [String]$listFilePath
)

gc $listFilePath | % { $_ }

# erase $listFilePath # you probably want this in your final script as good cleanup, commenting out for debug
pause

side note if interested, i use this format to drive a transcode.ps1 script which leverages handbrake.exe command line to bulk process .mov files (from point and shoot cameras) into mp4's.
customizing windows explorer with context menus like this starts to turn it into an efficient workflow space... further on that note, i like to use a left-right double explorer tool
here is another example, setting up zip files with an auto-extract script: https://beej126.github.io/windows-file-explorer-auto-extract-zips-like-mac-finder/

example 3 - files list passed directly to powershell script on command line as a string array

leaving off -f is what formats all the accumulated args together on one line that will come into powershell script as an array
using -q puts the specified quote character around EACH of the comma delimited file arguments accumulated, so it comes into the ps1 script as a true array

reg add "HKEY_CURRENT_USER\Software\Classes\*\shell\MyCommand\command" /f /ve /t REG_EXPAND_SZ /d "\"^%%bin^%%\SingleInstanceAccumulator\" -w -q:' \"-c:powershell -ExecutionPolicy bypass ^%%bin^%%\test.ps1 -filesArray $files\" \"%%1\""

note: -filesArray command line argument corresponds to test.ps1's $filesArray param shown next below

will execute like this:

powershell test.ps1 -filesArray 'filepath1', 'filepath2', 'filepath3'