Add an stderr redirection to a file after the actual command (redirections need to be the last in the line, order of them is not important unless you're using & to redirect one output to where ever another is going to). As an example, if you ran 'cat notthere.txt' and wanted the error to be saved to 'error.txt' in the same folder, you would redirect stderr (number 2; stdout is number 1, the usual output) like this:
Code:
cat notthere.txt 2>error.txt