Execution Preference
In MS-DOS, if a directory contains both a COM file and an EXE file with same name (not including extension), the COM file is preferentially selected for execution. For example, if a directory in the system path contains two files named foo.com and foo.exe, the following would execute foo.com:
A user wishing to run foo.exe can explicitly use the complete filename:
Taking advantage of this default behaviour, virus writers and other malicious programmers have used names like notepad.com for their creations, hoping that if it is placed in the same directory as the corresponding EXE file, a command or batch file may accidentally trigger their program instead of the text editor notepad.exe.
On Windows NT and derivatives (Windows 2000, Windows XP, Windows Vista, and Windows 7), the PATHEXT variable is used to override the order of preference (and acceptable extensions) for calling files without specifying the extension from the command line. The default value still places .com files before .exe files. This closely resembles a feature previously found in JP Software's line of extended command line processors 4DOS, 4OS2, and 4NT.
Read more about this topic: COM File
Famous quotes containing the words execution and/or preference:
“Some hours seem not to be occasion for any deed, but for resolves to draw breath in. We do not directly go about the execution of the purpose that thrills us, but shut our doors behind us and ramble with prepared mind, as if the half were already done. Our resolution is taking root or hold on the earth then, as seeds first send a shoot downward which is fed by their own albumen, ere they send one upward to the light.”
—Henry David Thoreau (1817–1862)
“There is nothing more likely to drive a man mad, than the being unable to get rid of the idea of the distinction between right and wrong, and an obstinate, constitutional preference of the true to the agreeable.”
—William Hazlitt (1778–1830)