subprocess.CalledProcessError: what *is* the error?

import subprocess cmd = "grep -r * | grep jquery" print cmd subprocess.check_output(cmd, shell=True) 

subprocess.CalledProcessError: Command 'grep -r * | grep jquery' returned non-zero exit status 1

I can execute that command in my shell without issues. How can I see the actual error in python?

The snippet is part of a larger script which takes multiple arguments and chains the grep commands + adds some excludes (I don't need to grep log files or minified JavaScript. Hence the pedantic syntax.

Python 2.7.10

2 Answers

Quoting docs:

If the return code was non-zero it raises a CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute and any output in the output attribute.

import subprocess cmd = "grep -r * | grep jquery" print cmd try: subprocess.check_output(cmd, shell=True) except subprocess.CalledProcessError as e: print e.returncode print e.output 

Of error message was printed to stderr, you need keyword argument stderr=subprocess.STDOUT.

There is no other source of 'what went wrong' besides return code and stdout / stderr.

"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.