Say I have a batch file for carrying out a long build and at the end it creates an EXE. If I forget to close the app down before I start the build, the link phase fails when it can't re-create the EXE.
I want to check if the EXE is open at the start of the build. I tried renaming the EXE file to itself but although this gives an access denied error the rename command (being an internal command) doesn't set %ErrorLevel%.
What's a non-destructive way of checking for an open file that sets %ErrorLevel% to a non-zero value?
The rename method didn't work for me (tested on Windows XP SP3). I started an arbitrary application and tried to rename it to itself. There was no error, no effect whatsoever.
However, this method did work:
COPY /B app.exe+NUL app.exe
When the application was running, this command produced me an error message. And when the application was unengaged, not only this command preserved the contents of file, but it also left the modification timestamp unchanged.
If I were you, therefore, I would probably use this command (at the beginning of the batch script, like you said) in this way:
COPY /B app.exe+NUL app.exe >NUL || (GOTO :EOF)
The || operator passes the control to the command/block next to it if the previous command has failed (raised the errorlevel value). Therefore, the above command would terminate the script if COPY failed (which it would if the file was open).
The error message would be preserved (because such messages are usually sent to the so called standard error device and are not discarded with the >NUL redirection, while other, non-error messages are typically sent to the standard output and so can be suppressed with >NUL) and serve as an explanation of the premature termination of the script. However, if you want to display your own message instead, you can try something like this:
COPY /B app.exe+NUL app.exe >NUL 2>NUL || (ECHO Target file inaccessible& GOTO :EOF)
While >NUL hides whatever is sent to the standard output, 2>NUL does the same for the standard error.