Question

I want to call a subprocess to backup mysql database.
A command line which ran fine in the terminal (and created a file named mydatabase.sql) is:

    mysqldump -uroot -ppassword --add-drop-database --database mydatabase > mydatabase.sql

Now the code to be ran by python to call a subprocess:

    args = shlex.split('mysqldump -uroot -ppassword --add-drop-database --database mydatabase > mydatabase.sql')
    subprocess.check_call(args)

The exeption is raised (no file created):

    Traceback (most recent call last):
      File "<pyshell#29>", line 1, in <module>
        subprocess.check_call(args)
      File "/usr/lib/python3.2/subprocess.py", line 485, in check_call
        raise CalledProcessError(retcode, cmd)
    subprocess.CalledProcessError: Command '['mysqldump', >'-uroot', '-ppassword', '--add-drop-database', '--database', >'mydatabase', '>', 'mydatabase.sql']' returned non-zero exit status 2

I have tried different ways, but they still don’t work:

    args = shlex.split('/opt/lampp/bin/mysqldump -uroot -ppassword --add-drop-database --database mydatabase > mydatabase.sql')
    subprocess.check_call(args)

or

    args = shlex.split('/opt/lampp/bin/mysqldump -uroot -ppassword --add-drop-database --database mydatabase > mydatabase.sql')
    subprocess.Popen(args)

I also tried with shell=True or or shell=False. In both cases, they still don’t work.

I have read the docs, google for the answer for my problem, but I haven’t got a clue how to show my problem. stackoverflow is probably my last hope.

Answer 1

the problem here is the way you’re redirecting the output.

• if you pass the command as a list of arguments, then ">" will always be interpreted as a literal >, no matter if you use shell=True or shell=False
• if you pass the command as a single string, then it hould work, but only if you have shell=True.

• the best way do do what you want would be to redirect the output to a file directly from python:

  args = shlex.split('/opt/lampp/bin/mysqldump -uroot -ppassword --add-drop-database --database mydatabase')
  output = open("mydatabase.sql", "w")
  subprocess.Popen(args, stdout=output)