Batch file to pull a random string from a file and loop a random number of times

You have a few problems:

• You define variable skip within a parenthesized block (the DO clause) and then attempt to use %skip% within the same loop. That can't work because the variable is expanded when the entire code block is parsed - before the value is set! Normally the solution is to use delayed expansion, but you can't used delayed expansion within FOR /F options. The solution is to CALL outside of the block.

• Your logic uses the same random number for each iteration. I interpret your stated requirement to mean you want to use a different random number for each iteration.

• Your GOTO breaks your FOR loop. The loop will not proceed to the next iteration if you issue a GOTO.

• Your computation for var2 is not good. It can fail if %RANDOM%*9 exceeds the maximum value for a 4 byte signed int. I also don't think it is giving the distribution of values that you want. You should use the mod operator like you do for the random line number.

• The value for the SKIP option must be >= 1. If you want 0 then you must omit the option entirely. Your isolated code does this properly, but your broken code is, ummmm broken :-)

Additional improvements:

• You compute the number of lines in the file each iteration. You only need to do that once.

• It is much more efficient to use FIND to count the number of lines and capture the value using FOR /F. FOR /F ignores blank lines, so I use FINDSTR to find all non empty lines, and pipe those results to FIND to get the count.

• Using TOKENS=* will strip leading spaces, whereas DELIMS= will preserve the whole line.

• The default EOL option is EOL=;, which means any line that begins with ; will be ignored. The weird syntax with carets before each space and equal and the absence of quotes is needed to set EOL to nothing.

• I added quotes around the file name and added the USEBACKQ option in case your file name includes spaces.

Here is a working solution

@echo off
setlocal
set "file=c:\myfile.txt"
for /f %%N in ('findstr "." "%file%"^|find /c /v ""') do set lines=%%N
set /a "iterations=%random% %% 8 + 2"
for /l %%N in (1 1 %iterations%) do call :printRandomLine
exit /b

:printRandomLine
set /a "skip=%random% %% %lines%"
if %skip% lss 1 (set "skip=") else set "skip=skip^=%skip%"
for /f usebackq^ %skip%^ delims^=^ eol^= %%A in ("%file%") do (
  echo %%A
  exit /b
)