What does /p stand for in set /p=? I know that / enables a switch, and I'm fairly sure that I know /a is for arithmetic. I've heard numerous rumours, some saying /p is for prompt, others stating it stands for print. The only reason I slightly doubt it is prompt is because in many cases it does not ask for a prompt, yet prints on the screen, such as
<nul set /p=This will not generate a new line But what I want to know is: Do we really know what it stands for?
12 Answers
The /P switch allows you to set the value of a variable to a line of input entered by the user. Displays the specified promptString before reading the line of input. The promptString can be empty.
Two ways I've used it... first:
SET /P variable= When batch file reaches this point (when left blank) it will halt and wait for user input. Input then becomes variable.
And second:
SET /P variable=<%temp%\filename.txt Will set variable to contents (the first line) of the txt file. This method won't work unless the /P is included. Both tested on Windows 8.1 Pro, but it's the same on 7 and 10.
For future reference, you can get help for any command by using the /? switch, which should explain what switches do what.
According to the set /? screen, the format for set /p is SET /P variable=[promptString] which would indicate that the p in /p is "prompt." It just prints in your example because <nul passes in a nul character which immediately ends the prompt so it just acts like it's printing. It's still technically prompting for input, it's just immediately receiving it.
NOTE: The answers below this point are for a previous version of the question.
/L in for /L generates a List of numbers.
From ping /?:
Usage: ping [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS] [-r count] [-s count] [[-j host-list] | [-k host-list]] [-w timeout] [-R] [-S srcaddr] [-4] [-6] target_name Options: -t Ping the specified host until stopped. To see statistics and continue - type Control-Break; To stop - type Control-C. -a Resolve addresses to hostnames. -n count Number of echo requests to send. -l size Send buffer size. -f Set Don't Fragment flag in packet (IPv4-only). -i TTL Time To Live. -v TOS Type Of Service (IPv4-only. This setting has been deprecated and has no effect on the type of service field in the IP Header). -r count Record route for count hops (IPv4-only). -s count Timestamp for count hops (IPv4-only). -j host-list Loose source route along host-list (IPv4-only). -k host-list Strict source route along host-list (IPv4-only). -w timeout Timeout in milliseconds to wait for each reply. -R Use routing header to test reverse route also (IPv6-only). -S srcaddr Source address to use. -4 Force using IPv4. -6 Force using IPv6. 
