Mini Shell

"""Common operations on Posix pathnames.

Instead of importing this module directly, import os and refer to
this module as os.path.  The "os.path" name is an alias for this
module on Posix systems; on other systems (e.g. Windows),
os.path provides the same operations in a manner specific to that
platform, and is an alias to another module (e.g. ntpath).

Some of this can actually be useful on non-Posix systems too, e.g.
for manipulation of the pathname component of URLs.
"""

# Strings representing various path-related bits and pieces.
# These are primarily for export; internally, they are hardcoded.
# Should be set before imports for resolving cyclic dependency.
curdir = '.'
pardir = '..'
extsep = '.'
sep = '/'
pathsep = ':'
defpath = '/bin:/usr/bin'
altsep = None
devnull = '/dev/null'

import os
import sys
import stat
import genericpath
from genericpath import *

__all__ = ["normcase","isabs","join","splitdrive","split","splitext",
           "basename","dirname","commonprefix","getsize","getmtime",
           "getatime","getctime","islink","exists","lexists","isdir","isfile",
           "ismount", "expanduser","expandvars","normpath","abspath",
           "samefile","sameopenfile","samestat",
           "curdir","pardir","sep","pathsep","defpath","altsep","extsep",
           "devnull","realpath","supports_unicode_filenames","relpath",
           "commonpath"]


def _get_sep(path):
    if isinstance(path, bytes):
        return b'/'
    else:
        return '/'

# Normalize the case of a pathname.  Trivial in Posix, string.lower on Mac.
# On MS-DOS this may also turn slashes into backslashes; however, other
# normalizations (such as optimizing '../' away) are not allowed
# (another function should be defined to do that).

def normcase(s):
    """Normalize case of pathname.  Has no effect under Posix"""
    return os.fspath(s)


# Return whether a path is absolute.
# Trivial in Posix, harder on the Mac or MS-DOS.

def isabs(s):
    """Test whether a path is absolute"""
    s = os.fspath(s)
    sep = _get_sep(s)
    return s.startswith(sep)


# Join pathnames.
# Ignore the previous parts if a part is absolute.
# Insert a '/' unless the first part is empty or already ends in '/'.

def join(a, *p):
    """Join two or more pathname components, inserting '/' as needed.
    If any component is an absolute path, all previous path components
    will be discarded.  An empty last part will result in a path that
    ends with a separator."""
    a = os.fspath(a)
    sep = _get_sep(a)
    path = a
    try:
        if not p:
            path[:0] + sep  #23780: Ensure compatible data type even if p is null.
        for b in map(os.fspath, p):
            if b.startswith(sep):
                path = b
            elif not path or path.endswith(sep):
                path += b
            else:
                path += sep + b
    except (TypeError, AttributeError, BytesWarning):
        genericpath._check_arg_types('join', a, *p)
        raise
    return path


# Split a path in head (everything up to the last '/') and tail (the
# rest).  If the path ends in '/', tail will be empty.  If there is no
# '/' in the path, head  will be empty.
# Trailing '/'es are stripped from head unless it is the root.

def split(p):
    """Split a pathname.  Returns tuple "(head, tail)" where "tail" is
    everything after the final slash.  Either part may be empty."""
    p = os.fspath(p)
    sep = _get_sep(p)
    i = p.rfind(sep) + 1
    head, tail = p[:i], p[i:]
    if head and head != sep*len(head):
        head = head.rstrip(sep)
    return head, tail


# Split a path in root and extension.
# The extension is everything starting at the last dot in the last
# pathname component; the root is everything before that.
# It is always true that root + ext == p.

def splitext(p):
    p = os.fspath(p)
    if isinstance(p, bytes):
        sep = b'/'
        extsep = b'.'
    else:
        sep = '/'
        extsep = '.'
    return genericpath._splitext(p, sep, None, extsep)
splitext.__doc__ = genericpath._splitext.__doc__

# Split a pathname into a drive specification and the rest of the
# path.  Useful on DOS/Windows/NT; on Unix, the drive is always empty.

def splitdrive(p):
    """Split a pathname into drive and path. On Posix, drive is always
    empty."""
    p = os.fspath(p)
    return p[:0], p


# Return the tail (basename) part of a path, same as split(path)[1].

def basename(p):
    """Returns the final component of a pathname"""
    p = os.fspath(p)
    sep = _get_sep(p)
    i = p.rfind(sep) + 1
    return p[i:]


# Return the head (dirname) part of a path, same as split(path)[0].

def dirname(p):
    """Returns the directory component of a pathname"""
    p = os.fspath(p)
    sep = _get_sep(p)
    i = p.rfind(sep) + 1
    head = p[:i]
    if head and head != sep*len(head):
        head = head.rstrip(sep)
    return head


# Is a path a symbolic link?
# This will always return false on systems where os.lstat doesn't exist.

def islink(path):
    """Test whether a path is a symbolic link"""
    try:
        st = os.lstat(path)
    except (OSError, ValueError, AttributeError):
        return False
    return stat.S_ISLNK(st.st_mode)

# Being true for dangling symbolic links is also useful.

def lexists(path):
    """Test whether a path exists.  Returns True for broken symbolic links"""
    try:
        os.lstat(path)
    except (OSError, ValueError):
        return False
    return True


# Is a path a mount point?
# (Does this work for all UNIXes?  Is it even guaranteed to work by Posix?)

def ismount(path):
    """Test whether a path is a mount point"""
    try:
        s1 = os.lstat(path)
    except (OSError, ValueError):
        # It doesn't exist -- so not a mount point. :-)
        return False
    else:
        # A symlink can never be a mount point
        if stat.S_ISLNK(s1.st_mode):
            return False

    if isinstance(path, bytes):
        parent = join(path, b'..')
    else:
        parent = join(path, '..')
    parent = realpath(parent)
    try:
        s2 = os.lstat(parent)
    except (OSError, ValueError):
        return False

    dev1 = s1.st_dev
    dev2 = s2.st_dev
    if dev1 != dev2:
        return True     # path/.. on a different device as path
    ino1 = s1.st_ino
    ino2 = s2.st_ino
    if ino1 == ino2:
        return True     # path/.. is the same i-node as path
    return False


# Expand paths beginning with '~' or '~user'.
# '~' means $HOME; '~user' means that user's home directory.
# If the path doesn't begin with '~', or if the user or $HOME is unknown,
# the path is returned unchanged (leaving error reporting to whatever
# function is called with the expanded path as argument).
# See also module 'glob' for expansion of *, ? and [...] in pathnames.
# (A function should also be defined to do full *sh-style environment
# variable expansion.)

def expanduser(path):
    """Expand ~ and ~user constructions.  If user or $HOME is unknown,
    do nothing."""
    path = os.fspath(path)
    if isinstance(path, bytes):
        tilde = b'~'
    else:
        tilde = '~'
    if not path.startswith(tilde):
        return path
    sep = _get_sep(path)
    i = path.find(sep, 1)
    if i < 0:
        i = len(path)
    if i == 1:
        if 'HOME' not in os.environ:
            import pwd
            try:
                userhome = pwd.getpwuid(os.getuid()).pw_dir
            except KeyError:
                # bpo-10496: if the current user identifier doesn't exist in the
                # password database, return the path unchanged
                return path
        else:
            userhome = os.environ['HOME']
    else:
        import pwd
        name = path[1:i]
        if isinstance(name, bytes):
            name = str(name, 'ASCII')
        try:
            pwent = pwd.getpwnam(name)
        except KeyError:
            # bpo-10496: if the user name from the path doesn't exist in the
            # password database, return the path unchanged
            return path
        userhome = pwent.pw_dir
    if isinstance(path, bytes):
        userhome = os.fsencode(userhome)
        root = b'/'
    else:
        root = '/'
    userhome = userhome.rstrip(root)
    return (userhome + path[i:]) or root


# Expand paths containing shell variable substitutions.
# This expands the forms $variable and ${variable} only.
# Non-existent variables are left unchanged.

_varprog = None
_varprogb = None

def expandvars(path):
    """Expand shell variables of form $var and ${var}.  Unknown variables
    are left unchanged."""
    path = os.fspath(path)
    global _varprog, _varprogb
    if isinstance(path, bytes):
        if b'$' not in path:
            return path
        if not _varprogb:
            import re
            _varprogb = re.compile(br'\$(\w+|\{[^}]*\})', re.ASCII)
        search = _varprogb.search
        start = b'{'
        end = b'}'
        environ = getattr(os, 'environb', None)
    else:
        if '$' not in path:
            return path
        if not _varprog:
            import re
            _varprog = re.compile(r'\$(\w+|\{[^}]*\})', re.ASCII)
        search = _varprog.search
        start = '{'
        end = '}'
        environ = os.environ
    i = 0
    while True:
        m = search(path, i)
        if not m:
            break
        i, j = m.span(0)
        name = m.group(1)
        if name.startswith(start) and name.endswith(end):
            name = name[1:-1]
        try:
            if environ is None:
                value = os.fsencode(os.environ[os.fsdecode(name)])
            else:
                value = environ[name]
        except KeyError:
            i = j
        else:
            tail = path[j:]
            path = path[:i] + value
            i = len(path)
            path += tail
    return path


# Normalize a path, e.g. A//B, A/./B and A/foo/../B all become A/B.
# It should be understood that this may change the meaning of the path
# if it contains symbolic links!

def normpath(path):
    """Normalize path, eliminating double slashes, etc."""
    path = os.fspath(path)
    if isinstance(path, bytes):
        sep = b'/'
        empty = b''
        dot = b'.'
        dotdot = b'..'
    else:
        sep = '/'
        empty = ''
        dot = '.'
        dotdot = '..'
    if path == empty:
        return dot
    initial_slashes = path.startswith(sep)
    # POSIX allows one or two initial slashes, but treats three or more
    # as single slash.
    # (see http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13)
    if (initial_slashes and
        path.startswith(sep*2) and not path.startswith(sep*3)):
        initial_slashes = 2
    comps = path.split(sep)
    new_comps = []
    for comp in comps:
        if comp in (empty, dot):
            continue
        if (comp != dotdot or (not initial_slashes and not new_comps) or
             (new_comps and new_comps[-1] == dotdot)):
            new_comps.append(comp)
        elif new_comps:
            new_comps.pop()
    comps = new_comps
    path = sep.join(comps)
    if initial_slashes:
        path = sep*initial_slashes + path
    return path or dot


def abspath(path):
    """Return an absolute path."""
    path = os.fspath(path)
    if not isabs(path):
        if isinstance(path, bytes):
            cwd = os.getcwdb()
        else:
            cwd = os.getcwd()
        path = join(cwd, path)
    return normpath(path)


# Return a canonical path (i.e. the absolute location of a file on the
# filesystem).

def realpath(filename):
    """Return the canonical path of the specified filename, eliminating any
symbolic links encountered in the path."""
    filename = os.fspath(filename)
    path, ok = _joinrealpath(filename[:0], filename, {})
    return abspath(path)

# Join two paths, normalizing and eliminating any symbolic links
# encountered in the second path.
def _joinrealpath(path, rest, seen):
    if isinstance(path, bytes):
        sep = b'/'
        curdir = b'.'
        pardir = b'..'
    else:
        sep = '/'
        curdir = '.'
        pardir = '..'

    if isabs(rest):
        rest = rest[1:]
        path = sep

    while rest:
        name, _, rest = rest.partition(sep)
        if not name or name == curdir:
            # current dir
            continue
        if name == pardir:
            # parent dir
            if path:
                path, name = split(path)
                if name == pardir:
                    path = join(path, pardir, pardir)
            else:
                path = pardir
            continue
        newpath = join(path, name)
        if not islink(newpath):
            path = newpath
            continue
        # Resolve the symbolic link
        if newpath in seen:
            # Already seen this path
            path = seen[newpath]
            if path is not None:
                # use cached value
                continue
            # The symlink is not resolved, so we must have a symlink loop.
            # Return already resolved part + rest of the path unchanged.
            return join(newpath, rest), False
        seen[newpath] = None # not resolved symlink
        path, ok = _joinrealpath(path, os.readlink(newpath), seen)
        if not ok:
            return join(path, rest), False
        seen[newpath] = path # resolved symlink

    return path, True


supports_unicode_filenames = (sys.platform == 'darwin')

def relpath(path, start=None):
    """Return a relative version of a path"""

    if not path:
        raise ValueError("no path specified")

    path = os.fspath(path)
    if isinstance(path, bytes):
        curdir = b'.'
        sep = b'/'
        pardir = b'..'
    else:
        curdir = '.'
        sep = '/'
        pardir = '..'

    if start is None:
        start = curdir
    else:
        start = os.fspath(start)

    try:
        start_list = [x for x in abspath(start).split(sep) if x]
        path_list = [x for x in abspath(path).split(sep) if x]
        # Work out how much of the filepath is shared by start and path.
        i = len(commonprefix([start_list, path_list]))

        rel_list = [pardir] * (len(start_list)-i) + path_list[i:]
        if not rel_list:
            return curdir
        return join(*rel_list)
    except (TypeError, AttributeError, BytesWarning, DeprecationWarning):
        genericpath._check_arg_types('relpath', path, start)
        raise


# Return the longest common sub-path of the sequence of paths given as input.
# The paths are not normalized before comparing them (this is the
# responsibility of the caller). Any trailing separator is stripped from the
# returned path.

def commonpath(paths):
    """Given a sequence of path names, returns the longest common sub-path."""

    if not paths:
        raise ValueError('commonpath() arg is an empty sequence')

    paths = tuple(map(os.fspath, paths))
    if isinstance(paths[0], bytes):
        sep = b'/'
        curdir = b'.'
    else:
        sep = '/'
        curdir = '.'

    try:
        split_paths = [path.split(sep) for path in paths]

        try:
            isabs, = set(p[:1] == sep for p in paths)
        except ValueError:
            raise ValueError("Can't mix absolute and relative paths") from None

        split_paths = [[c for c in s if c and c != curdir] for s in split_paths]
        s1 = min(split_paths)
        s2 = max(split_paths)
        common = s1
        for i, c in enumerate(s1):
            if c != s2[i]:
                common = s1[:i]
                break

        prefix = sep if isabs else sep[:0]
        return prefix + sep.join(common)
    except (TypeError, AttributeError):
        genericpath._check_arg_types('commonpath', *paths)
        raise