Batch file: "Missing Operator" error while incrementing a value in a textfile?

Question

This is a syntax question related this answer from crono: https://stackoverflow.com/a/40869/1783806

@echo off

for /f " delims==" %%i in (counter.txt) do set /A temp_counter= %%i+1
echo %temp_counter% > counter.txt

assuming the count.bat and counter.txt are located in the same directory.

I get a "missing operator" error when I change the directory structure.

This is what CMD returns when I changed the structure to "C:\foo\counter.txt":

C:\foo>for /F " delims==" %i in ("C:\foo\counter.txt") do set /A temp_counter=%i+1

C:\foo>set /A temp_counter=C:\foo\counter.txt+1
Missing operator.

C:\foo>echo 0  1>"C:\foo\counter.txt"

How do I get the same code to work if the files are in different directories?

Can someone also explain why the error is occurring?

Answer 1

In the first code you do not quote the IN() clause, so it is treated as a file.

In the second code you do quote the IN() clause, so it is treated as a string literal instead of a file. If you want to use quotes around the file name then you must add the USEBACKQ option to your FOR /F options. Type HELP FOR for more info on the many variations of the FOR command.