subprocess module in python

Question

I have to connect to a sybase database and run a simple select query using python script

On my server isql command can run only from sybase bin directory, so i have to cd to that directory before firing the query.

---------------------------Edited-----------------------------

Uptill now i'm able to do this:-

#!/usr/bin/python
 import subprocess
 path = "path/to/sybase/bin"
 os.chdir(path)
 arguments = ['./isql',"-S server_name", "-U user", "-P password", "-D database","""<<EOF
 SELECT * FROM sometable
 go
 EOF"""]
 ps = subprocess.Popen(arguments)
 out = ps.communicate()
 print out

The errors are just out of my understanding capability :(

Traceback (most recent call last):
File "./test_db.py", line 8, in ?
ps = subprocess.Popen(arguments)
File "/usr/lib64/python2.4/subprocess.py", line 542, in __init__
errread, errwrite)
File "/usr/lib64/python2.4/subprocess.py", line 975, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory

I'm able to do this outside my python script using isql command on my unix terminal

how can i use isql in python subprocess module?

• confused_at_times: Use import os; os.chdir(path) to change path.
• confused_at_times: Remove parenthesis from inside string. Infact, you can remove the square brackets completely.
• Bad_Coder: that didn't work, same errors
• confused_at_times: Seems isql may not exist in that folder. Check me answer update.

Answer 1

There is a particular Popen argument for that: cwd, as mentioned here. Provide your command using an array and then the cwd parameter with where the command must be executed:

subprocess.Popen(['ls', '-l'], cwd="/path/to/folder")

• dano: Yes. Most of the other answers here missed that you're passing your command as a string without using shell=True, which won't work properly. When you're using shell=False, you have to pass your command and its arguments as a list.
• dano: Also, if you need some help splitting your command up properly into a list, you can use the shlex.split() function: docs.python.org/2/library/shlex.html#shlex.split
• marcelocra: Like @dano mentioned, you can give the command as you would in a shell with the option shell=True (though the documentation says this is unsafe). Other thing that could work to use a dedicated library like python-sybase.sourceforge.net/examples.html
• dano: @Disturbed_Entity If you run your command using only subprocess.Popen(['./isql']) (none of the args) does it work?

Answer 2

Popen only takes one args argument, for the command to run. You could try calling a shell with both the cd and isql commands as arguments, but changing the working directory from python is probably simpler

For the former approach:

subprocess.Popen('/bin/sh -c "cd /path/to/... && isql -arg1..'...)

for the latter:

os.chdir('/path/to...')
subprocess.Popen('isql -arg1..'...)

• Bad_Coder: how do i pass this as an argument? ['isql', '-S server' -U %s -P %s -D %s <<EOF SELECT * FROM UniqueIDRange EOF' % (server,user,passwd,database)]

Answer 3

Try:

import os
import subprocess
os.chdir('/path/to/sybase/bin')
if os.path.exists('isql') or os.path.exists(os.path.join('/path/to/sybase/bin', 'isql')):
 ps = subprocess.Popen('isql -S %s -U %s -P %s -D %s <<EOF SELECT * FROM sometable EOF' % (server,user,passwd,database), stdout=subprocess.PIPE, shell=True)
 out, err = ps.communicate()
else:
 print "isql does not exists in this folder"

I am not super experienced with subprocess but this is how I generally use it on the odd occasion. Hopefully someone else can give a better answer/explanation.

Edit: removed the square brackets to remove confusion.

Answer 4

i know it's been long but just wanted to close this question

from subprocess import Popen, PIPE
from textwrap import dedent
isql = Popen(['./isql', '-I', '/app/sybase/...',
 '-S', mdbserver,
 '-U', muserid,
 '-P', password, ...,
 '-w', '99999'], stdin=PIPE, stdout=PIPE, cwd=sybase_path)
output = isql.communicate(dedent("""\
 SET NOCOUNT ON
 {}
 go
""".format(User_Query)))[0]