sh/bat hybrid that checks available commands. Despite its hackish look, it was tested under Windows XP, wine, ksh, zsh, dash and bash.

exists.cmd

: ::\
@echo off
rem () ( command -v $1 >/dev/null 2>&1; return $? )

rem : "Usage sh:  $ sh exists.cmd ls && echo exists "
rem : "Usage bat: > exists.cmd notepad              "
rem : "           > echo %ErrorLevel%               "

rem $1 <<REM
:exists
	if exist %1 exit /b 0
	for %%P in ("%PATH:;=" "%") do (
		if exist %%~P\%1 ( exit /b 0 )
		call :exists_ext %%~P\%1
		if not errorlevel 1 ( exit /b 0 )
	)
	exit /b 1
:exists_ext
	for %%P in ("%PATHEXT:;=" "%") do (
		if exist %1%%~P ( exit /b 0 )
	)
	exit /b 1
REM