views:

27

answers:

3

What I'd like to achieve is the launch of the following shell command:

mysql -h hostAddress -u userName -p userPassword 
databaseName < fileName

From within a python 2.4 script with something not unlike:

cmd = ["mysql", "-h", ip, "-u", mysqlUser, dbName, "<", file]
subprocess.call(cmd)

This pukes due to the use of the redirect symbol (I believe) - mysql doesn't receive the input file.

I've also tried:

subprocess.call(cmd, stdin=subprocess.PIPE)

no go there ether

Can someone specify the syntax to make a shell call such that I can feed in a file redirection ?

Thanks in advance.

+3  A: 

You have to feed the file into mysql stdin by yourself. This should do it.

import subprocess
...
filename = ...
cmd = ["mysql", "-h", ip, "-u", mysqlUser, dbName]
f = open(filename)
subprocess.call(cmd, stdin=f)
Constantin
+2  A: 

The symbol < has this meaning (i. e. reading a file to stdin) only in shell. In Python you should use either of the following:

1) Read file contents in your process and push it to stdin of the child process:

fd = open(filename,  'rb')
try:
    subprocess.call(cmd, stdin=fd)
finally:
    fd.close()

2) Read file contents via shell (as you mentioned), but redirect stdin of your process accordingly:

# In file myprocess.py
subprocess.call(cmd, stdin=subprocess.PIPE)

# In shell command line
$ python myprocess.py < filename
Andrey Vlasovskikh
Minor correction: there is no `with` statement in 2.4.
Constantin
@Constantin Thanks.
Andrey Vlasovskikh
It may be related to my config but specifying subprocess.PIPE as stdin just hung. Reading as a file worked well. Thanks!
Sean
@Sean, Possibly `subprocess.call(cmd, stdin=subprocess.PIPE)` in "2)" was meant to be `subprocess.call(cmd, stdin=sys.stdin)`?
Constantin
@Constantin I believe you are correct yes. Good catch.
Sean
A: 

As Andrey correctly noticed, the < redirection operator is interpreted by shell. Hence another possible solution:

import os
os.system("mysql -h " + ip + " -u " + mysqlUser + " " + dbName)

It works because os.system passes its argument to the shell.

Note that I assumed that all used variables come from a trusted source, otherwise you need to validate them in order to prevent arbitrary code execution. Also those variables should not contain whitespace (default IFS value) or shell special characters.

Roman Cheplyaka
That makes os.system sound far more convenient then subprocess. I was mistaken to think that os.system was being Deprecated. Thanks for the answer.
Sean
Well, I would prefer subprocess-solution myself, it's superior in a number of ways (e.g. it should be more portable).
Roman Cheplyaka