Randomly select a line out of a text file and set that line as a variable

Question

How to randomly select a line/ip out of a text file, and set it as a variable.

I mean something like:

set IP=TheLine/IPFromOfTheFile

Answer 1

Firstly you need to know the number of lines present in the text file textfile.txt:

for /F %%N in ('type "textfile.txt" ^| find /C /V ""') do set NUM=%%N

Then calculate the random number in the range from 0 to NUM-1:

set /A RND=%RANDOM%%%NUM

Finally pick the line from the text file and store it in LINE. RND holds the number of lines to skip by the for /F loop:

if %RND% EQU 0 (set "SKIP=") else (set "SKIP=skip=%RND% ")
for /F "usebackq %SKIP%delims=" %%L in ("textfile.txt") do (
    set "LINE=%%L"
    goto :NEXT
)
:NEXT

This relies on the fact that the text file does not contain any empty lines.