First off, love your new sig - 'Swiss Army Nerd Idiot' ;-)

I use Windows (XP with Activestate 5.10.1) all the time for my Perl development. I believe when Windows gets a program name without extension (your example was 'perl'), the 'search' is similar to the following pseudo-code:

PROGRAM = perl
PATH = '.' + %PATH%
foreach PATH in %PATH% {
    foreach EXTENSION in %PATHEXT% {
        TRY PATH\perl.EXTENSION
    }
}
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That is to say, search the local directory first, even if it isn't in your path (you won't see '.' when you type 'path' from cmd.exe). Try appending each extension in the %PATHEXT% environment variable to the program name and search current directory followed by each directory in your path.

Values of %PATH% and %PATHEXT% can be found by:

C:\> set PATH
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This is *WAY* beyond Perl scope, but a nifty batch file I found and modified (I would give credit if only I remembered where I found this, Google 'which.bat' and a few different sites with different versions of this come up) acts much like the 'which' command on Unix. Save as 'which.bat' and put it in a directory in your %PATH% environment variable.

@echo off

setlocal

  REM
  REM Help
  REM
if {%1}=={/?} goto HELP
if {%1}=={--help} goto HELP

  REM
  REM Check args
  REM
if {%1}=={} goto SYNTAX_ERROR
if not {%3}=={} goto SYNTAX_ERROR

  REM
  REM Start Get ARGS
  REM
:ARGS
if {%1}=={} goto EXECUTE

    set string=%1

      REM
      REM If the first character in arg is a -, it's a switch
      REM
    if "!string:~0,1!"=="-" (

        set position=0

        :LOOP
          REM
          REM If the character indicated by the string is a space, ech
+o a return;
          REM else, just echo the character
          REM
        if "!string:~%position%,1!"=="" goto SLIDE
        if "!string:~%position%,1!"=="a" set WHICHALL=YES&& goto INCR
        if "!string:~%position%,1!"=="-" goto INCR
        echo %0: unknown option -- "!string:~%position%,1!"

        :INCR
          REM
          REM Increment the position in the string and loop
          REM
        set /a position=%position%+1
        goto LOOP

    ) else set batchparams=%1

:SLIDE
shift
goto ARGS

REM -------------------------------------------------------

:EXECUTE
set errorlevel_=0

set program_=%batchparams%

:: Any input with wildcard or path characters is a syntax error.
for /F %%i in ('echo ":" ^& echo "\" ^& echo "*" ^& echo "/" ^& echo "
+?" ^& echo "," ^& echo ";"') do (
  echo %program_% | find %%i > nul && goto SYNTAX_ERROR
)

:: This variable stores the current directory, followed by PATH, as
:: the search order to search for program files.  Quotes are added
:: between each ';' to handle paths with spaces.
set path_="%cd%";"%PATH:;=";"%"

:: Lowercase the path extensions.  This is needed to perform
:: case-insensitive extension comparisons.
set path_ext_=%PATHEXT%
set path_ext_=%path_ext_:A=a%
set path_ext_=%path_ext_:B=b%
set path_ext_=%path_ext_:C=c%
set path_ext_=%path_ext_:D=d%
set path_ext_=%path_ext_:E=e%
set path_ext_=%path_ext_:F=f%
set path_ext_=%path_ext_:G=g%
set path_ext_=%path_ext_:H=h%
set path_ext_=%path_ext_:I=i%
set path_ext_=%path_ext_:J=j%
set path_ext_=%path_ext_:K=k%
set path_ext_=%path_ext_:L=l%
set path_ext_=%path_ext_:M=m%
set path_ext_=%path_ext_:N=n%
set path_ext_=%path_ext_:O=o%
set path_ext_=%path_ext_:P=p%
set path_ext_=%path_ext_:Q=q%
set path_ext_=%path_ext_:R=r%
set path_ext_=%path_ext_:S=s%
set path_ext_=%path_ext_:T=t%
set path_ext_=%path_ext_:U=u%
set path_ext_=%path_ext_:V=v%
set path_ext_=%path_ext_:W=w%
set path_ext_=%path_ext_:X=x%
set path_ext_=%path_ext_:Y=y%
set path_ext_=%path_ext_:Z=z%

:: If the program name has an extension, we want to verify that the
:: extension is one of those in the path_ext_ environment variable.
:: If it is, then this script will only search for that program with
:: that specific extension.  If not, all of the extensions in the
:: path_ext_ variable will be tested, appended to the program name.

:: Get the extension if any from the program name.
for /F %%i in ("%program_%") do (set extension_=%%~xi)

:: Comparing the program extension against the list of executable
:: extensions.  If the extension is found, then path_ext_ will just
:: have that extension.
set path_ext_=%path_ext_:;= %
if not {%extension_%}=={} (
  for %%i in (%path_ext_%) do if "%%i"=="%extension_%" (
    set path_ext_=%extension_%
    for /F %%i in ("%program_%") do (set program_=%%~ni)
  )
)

:: This will prepend a path prefix to the program name and append an
:: executable extension for every path and extension found in the
:: path_ and path_ext_ variables.
for %%i in (%path_%) do (
  for %%j in (%path_ext_%) do (
    if exist "%%~i\%program_%%%~j" (
      set found_=%%~i\%program_%%%~j
      if {%WHICHALL%}=={YES} echo !found_!
      if not {%WHICHALL%}=={YES} goto FOUND
    )
  )
)

if "%found_%"=="" echo '%batchparams%' not found.
goto END

:FOUND
echo %found_%
goto END

:SYNTAX_ERROR
echo which: The syntax of the command is incorrect. 1>&2
goto ERROR

:ERROR
set errorlevel_=1

:END
exit /B %errorlevel_%

:HELP
echo.
echo %0 will find the program file that is used when run from 
echo a DOS prompt.  It will search the current directory and the 
echo PATH environment variable directories for the program using 
echo the extensions found in the PATHEXT environment variable.
echo.
echo     USAGE:
echo.
echo     %0 [options] ^<program^>
echo.
echo     -a            Print all matches in order; don't stop at first
+.
echo.
echo     program       An external command, program, or script.
echo.
echo     If you want to find a program with a particular extension,
echo     include that extension in the program name and the 'which' 
echo     command will only search for a program file with that extensi
+on.
echo.
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Now, from cmd.exe:

\\vmware-host\Shared Folders Z:\mvincent\tmp> which perl
Z:\mvincent\tmp\perl.bat

\\vmware-host\Shared Folders Z:\mvincent\tmp> which -a perl
Z:\mvincent\tmp\perl.bat
C:\Perl\bin\perl.exe
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