IPython/utils/process.py

# encoding: utf-8
"""
Utilities for working with external processes.
"""

#-----------------------------------------------------------------------------
#  Copyright (C) 2008-2009  The IPython Development Team
#
#  Distributed under the terms of the BSD License.  The full license is in
#  the file COPYING, distributed as part of this software.
#-----------------------------------------------------------------------------

#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------
from __future__ import print_function

# Stdlib
import os
import sys
import shlex

# Our own
if sys.platform == 'win32':
    from ._process_win32 import _find_cmd, system, getoutput, AvoidUNCPath
else:
    from ._process_posix import _find_cmd, system, getoutput

from ._process_common import getoutputerror
from IPython.utils import py3compat

#-----------------------------------------------------------------------------
# Code
#-----------------------------------------------------------------------------


class FindCmdError(Exception):
    pass


def find_cmd(cmd):
    """Find absolute path to executable cmd in a cross platform manner.
    
    This function tries to determine the full path to a command line program
    using `which` on Unix/Linux/OS X and `win32api` on Windows.  Most of the
    time it will use the version that is first on the users `PATH`.  If
    cmd is `python` return `sys.executable`.

    Warning, don't use this to find IPython command line programs as there
    is a risk you will find the wrong one.  Instead find those using the
    following code and looking for the application itself::
    
        from IPython.utils.path import get_ipython_module_path
        from IPython.utils.process import pycmd2argv
        argv = pycmd2argv(get_ipython_module_path('IPython.frontend.terminal.ipapp'))

    Parameters
    ----------
    cmd : str
        The command line program to look for.
    """
    if cmd == 'python':
        return os.path.abspath(sys.executable)
    try:
        path = _find_cmd(cmd).rstrip()
    except OSError:
        raise FindCmdError('command could not be found: %s' % cmd)
    # which returns empty if not found
    if path == b'':
        raise FindCmdError('command could not be found: %s' % cmd)
    return os.path.abspath(path)


def pycmd2argv(cmd):
    r"""Take the path of a python command and return a list (argv-style).

    This only works on Python based command line programs and will find the
    location of the ``python`` executable using ``sys.executable`` to make
    sure the right version is used.

    For a given path ``cmd``, this returns [cmd] if cmd's extension is .exe,
    .com or .bat, and [, cmd] otherwise.  

    Parameters
    ----------
    cmd : string
      The path of the command.

    Returns
    -------
    argv-style list.
    """
    ext = os.path.splitext(cmd)[1]
    if ext in ['.exe', '.com', '.bat']:
        return [cmd]
    else:
        if sys.platform == 'win32':
            # The -u option here turns on unbuffered output, which is required
            # on Win32 to prevent wierd conflict and problems with Twisted.
            # Also, use sys.executable to make sure we are picking up the 
            # right python exe.
            return [sys.executable, '-u', cmd]
        else:
            return [sys.executable, cmd]


def arg_split(s, posix=False):
    """Split a command line's arguments in a shell-like manner.

    This is a modified version of the standard library's shlex.split()
    function, but with a default of posix=False for splitting, so that quotes
    in inputs are respected."""

    # Unfortunately, python's shlex module is buggy with unicode input:
    # http://bugs.python.org/issue1170
    # At least encoding the input when it's unicode seems to help, but there
    # may be more problems lurking.  Apparently this is fixed in python3.
    is_unicode = False
    if (not py3compat.PY3) and isinstance(s, unicode):
        is_unicode = True
        s = s.encode('utf-8')
    lex = shlex.shlex(s, posix=posix)
    lex.whitespace_split = True
    tokens = list(lex)
    if is_unicode:
        # Convert the tokens back to unicode.
        tokens = [x.decode('utf-8') for x in tokens]
    return tokens


def abbrev_cwd():
    """ Return abbreviated version of cwd, e.g. d:mydir """
    cwd = os.getcwdu().replace('\\','/')
    drivepart = ''
    tail = cwd
    if sys.platform == 'win32':
        if len(cwd) < 4:
            return cwd
        drivepart,tail = os.path.splitdrive(cwd)


    parts = tail.split('/')
    if len(parts) > 2:
        tail = '/'.join(parts[-2:])

    return (drivepart + (
        cwd == '/' and '/' or tail))