cmd = "grep -r * | grep jquery"
"non-zero exit status" means that the command you ran indicated a status other than success. For
grep, the documentation explicitly indicates that an exit status of 1 indicates no lines were found, whereas an exit status more than 1 indicates that some other error took place.
To quote the manual:
EXIT STATUS - The grep utility exits with one of the following values:
0 One or more lines were selected. 1 No lines were selected. >1 An error occurred.
By the way -- if you want to look for the string
jquery in all files under the current directory (recursively), use
grep -r jquery .;
grep -r * searches for the name of the first file in your directory inside the contents of all other files in your directory.