Not included with Windows? The DOS command
debug is part of the default Windows install at
%windir%\system32\debug.exe and it does primitive hex dumps via the "d" (dump) command. I do not know the command to dump an entire file, but I know that debug is scriptable (
"debug <infile >outfile"), though there may be limits on filesize.
Interestingly, the version of debug.exe included with Windows 7 (and every version below that) is exactly the same code and file as the version included with MS-DOS 5.0! See
http://thestarman.pcministry.com/asm/debug/debug.htm#NT
For an external, free command-line hex dump utility, I use xd, available with source code from
http://xd.adoxa.cjb.net