Question

searched this site and others – no joy.

:: first for loop
for /L %%x in (1,1,2) do (
generic-executable.output > grab1-%%x.txt

:: second, nested for loop
for /f "delims=" %%i in (grab1-%%x.txt) do (set grab1=%%i)
echo variable string is %grab1%%x%

generic-executable.output > grab2-%%x.txt
for /f "delims=" %%i in (grab2-%%x.txt) do (set grab2=%%i)
echo variable string is %grab2%%x%
)

Trying to run a nested for loop that will

1) write data to the file

2) take data from the file and save it to another variable.

The names of the end variables should be a concatenation of each of the for loops (i.e. grab1-1, 2-1, 1-2, 2-2).

Saving the data to the variables is no problem, formatting the variables to recall the data IS.

I’m most likely missing something in the formatting of the concatenated variable. I’ve tried single ', double ", ^, !, one %, two %, backslash, ACK!! … the closest I’ve gotten is

echo %grab1-%%x

gave:

%grab1-1

I’d appreciate any tips you can provide.

Thanks,
Dave

Answer 1

You have run into a classic stumbling block for batch newbies: You cannot set a variable within a loop (within parentheses) and then access the value using %var% within the same loop. The Entire loop (parenthesized block of code) is parsed in one pass, and %var% is expanded at parse time. So you see the value of var as it was prior to the loop executing.

The solution is to enable delayed expansion using setlocal enableDelayedExpansion near the top of your script, and then expand the variable using delayed expansion as !var!. Delayed expansion means the value is expanded at run time – exactly what you want.

I believe this is what you were trying to achieve

setlocal enableDelayedExpansion
for /L %%x in (1,1,2) do (

  genericOutput1.exe > grab1-%%x.txt
  for /f "delims=" %%i in (grab1-%%x.txt) do set "grab1-%%x=%%i"
  echo grab1-%%x variable string is !grab1-%%x!

  genericOutput2.exe > grab2-%%x.txt
  for /f "delims=" %%i in (grab2-%%x.txt) do set "grab2-%%x=%%i"
  echo grab2-%%x variable string is !grab2-%%x!
)

::List all of the grab variable defined
set grab

You don’t need to save the output of your executables to a file. (Unless of course that is your requirement). You can use FOR /F to process the output directly. The FOR command has many variants that look nearly identical, yet behave very differently. This variant uses single quotes to cause FOR /F to process a command.

setlocal enableDelayedExpansion
for /L %%x in (1,1,2) do (

  for /f "delims=" %%i in ('genericOutput1.exe') do set "grab1-%%x=%%i"
  echo grab1-%%x variable string is !grab1-%%x!

  for /f "delims=" %%i in ('genericOutput1.exe') do set "grab2-%%x=%%i"
  echo grab2-%%x variable string is !grab2-%%x!
)

::List all of the grab variable defined
set grab

Note that FOR /F will iterate each line (whether it be from a text file or from command output). Your algorithm will only save and print the content of the last line – each successive line will overwrite the value from the prior line.