shlib 0.0.4

shell library

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Shell Library
=============

A light-weight package with few dependencies that allows users to do
shell-script like things relatively easily in Python. Is a natural complement to
the pathlib library. Pathlib does pretty much what you would like to do with
a single path; shlib does similar things with many paths at once. For example,
with pathlib you can remove (unlink) a single file, but with shlib you can
remove many files at once.

Writing programs that substantially interact with the file system can be
surprisingly painful in Python because the code that is used to do so is spread
over many packages and those packages are not very compatible with each other
nor do they follow the conventions of the corresponding shell commands.

This package, shlib, attempts to address those issues by providing one package
that combines the commonly used utilities for interacting with the filesystem
that follows the conventions used by the corresponding shell commands.

It consists of replacements for some very common Unix utilities that interact
with the filesystem, such as cp, mv, rm, ln, and mkdir. These tend to be less
fussy than their command line counter parts. For example, rm deletes both files
and directories without distinction and will not complain if the file or
directory does not exist. Similarly mkdir will create any child directories
needed and will not complain if the directory already exists.

Finally, it provides several ways to run external programs.

Each feature is designed to allow you to express your desires simply and
efficiently without worrying too much about exceptions.

Most of the functions in this package take paths to files or directories. Those
paths may be specified either as strings or pathlib paths. Many of the functions
accept multiple paths, and those can be specified either as an array or as
individual arguments. Several of the functions return either a path or
a collection of paths. These paths are returned as pathlib paths.


Installation
------------

Use 'pip3 install shlib' to install. Requires Python3.5 or better.


System Utility Functions
------------------------

Copy (cp)
~~~~~~~~~

Copy files or directories::

cp(src, ..., dest)

or::

cp([src, ...], dest)

Copy all source items, whether they be files or directories to dest. If there is
more than one src item, then dest must be a directory and the copies will be
placed in that directory. The src arguments may be strings, pathlib paths, or
collections of strings and paths. The dest must be a string or path.

Example:

.. code-block:: python

>>> from shlib import cartesian_product, cp, ls, lsd, lsf, mkdir, Path, rm, touch
>>> testdir = 'testdir'
>>> rm(testdir)
>>> mkdir(testdir)
>>> files = cartesian_product(testdir, ['f1', 'f2'])
>>> touch(files)
>>> dirs = cartesian_product(testdir, ['d1', 'd2'])
>>> mkdir(dirs)
>>> print(sorted(str(e) for e in ls(testdir)))
['testdir/d1', 'testdir/d2', 'testdir/f1', 'testdir/f2']

>>> cp('testdir/f1', 'testdir/f4')
>>> print(sorted(str(f) for f in lsf(testdir)))
['testdir/f1', 'testdir/f2', 'testdir/f4']

>>> dest1 = Path(testdir, 'dest1')
>>> mkdir(dest1)
>>> cp(files, dest1)
>>> print(sorted(str(f) for f in lsf(dest1)))
['testdir/dest1/f1', 'testdir/dest1/f2']

>>> cp(dirs, dest1)
>>> print(sorted(str(d) for d in lsd(dest1)))
['testdir/dest1/d1', 'testdir/dest1/d2']

>>> f1, f2 = tuple(files)
>>> dest2 = Path(testdir, 'dest2')
>>> mkdir(dest2)
>>> cp(f1, f2, dest2)
>>> print(sorted(str(f) for f in lsf(dest2)))
['testdir/dest2/f1', 'testdir/dest2/f2']

>>> dest3 = Path(testdir, 'dest3')
>>> mkdir(dest3)
>>> cp([f1, f2], dest3)
>>> print(sorted(str(f) for f in lsf(dest3)))
['testdir/dest3/f1', 'testdir/dest3/f2']


Move (mv)
~~~~~~~~~

Move files or directories::

mv(src, ..., dest)

Move all source items, whether they be files or directories to dest. If there is
more than one src item, then dest must be a directory and everything will be
placed in that directory. The src arguments may be strings or lists of strings.
The dest must be a string.

.. code-block:: python

>>> from shlib import cartesian_product, mkdir, Path, ls, lsd, lsf, mv, rm
>>> testdir = 'testdir'
>>> rm(testdir)
>>> mkdir(testdir)
>>> files = cartesian_product(testdir, ['f1', 'f2'])
>>> touch(files)
>>> dirs = cartesian_product(testdir, ['d1', 'd2'])
>>> mkdir(dirs)
>>> print(sorted(str(e) for e in ls(testdir)))
['testdir/d1', 'testdir/d2', 'testdir/f1', 'testdir/f2']

>>> dest = Path(testdir, 'dest')
>>> mkdir(dest)
>>> mv(files, dest) # move a list of files
>>> print(sorted(str(f) for f in lsf(dest)))
['testdir/dest/f1', 'testdir/dest/f2']

>>> mv(dirs, dest) # move a list of directories
>>> print(sorted(str(d) for d in lsd(dest)))
['testdir/dest/d1', 'testdir/dest/d2']


Remove (rm)
~~~~~~~~~~~

Remove files or directories::

rm(path, ...)

Delete all files and directories given as arguments. Does not complain if any of
the items do not exist. Each argument must be either a string or a list of
strings.

.. code-block:: python

>>> print(sorted(str(e) for e in ls(testdir)))
['testdir/dest']

>>> print(sorted(str(e) for e in ls(dest)))
['testdir/dest/d1', 'testdir/dest/d2', 'testdir/dest/f1', 'testdir/dest/f2']

>>> rm(lsf(dest))
>>> print(sorted(str(e) for e in ls(dest)))
['testdir/dest/d1', 'testdir/dest/d2']

>>> rm(dest)
>>> print(sorted(str(e) for e in ls(testdir)))
[]

>>> rm(testdir)

Link (ln)
~~~~~~~~~~~

Create a symbolic link::

ln(src, link)

Creates a symbolic link *link* that points to *src*. Each argument must be
either a string.


Make File (touch)
~~~~~~~~~~~~~~~~~

Create a new empty file or update the timestamp on an existing file::

touch(path, ...)

Each argument must be either a string or a list of strings.


Make Directory (mkdir)
~~~~~~~~~~~~~~~~~~~~~~

Create an empty directory::

mkdir(path, ...)

For each argument it creates a directory and any needed parent directories.
Returns without complaint if the directory already exists. Each argument must be
either a string or a list of strings.


List Directory (ls, lsd, lsf)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

List a directory::

ls(path, ... [<kwargs>])
lsd(path, ... [<kwargs>])
lsf(path, ... [<kwargs>])

The first form returns a list of all items found in a directory. The second
returns only the directories, and the third returns only the files.

One or more paths may be specified using unnamed arguments. The paths may be
strings or pathlib paths, or collections of those. If no paths are not given,
the current working directory is assumed.

The remaining arguments must be specified as keyword arguments.

::

select=<glob-str>

If *select* is specified, an item is returned only if it matches the given
pattern. Using '**' in *select* enables a recursive walk through a directory
and all its subdirectories. Using '**' alone returns only directories whereas
'**/*' returns files and directories.

::

reject=<glob-str>

If *reject* is specified, an item is not returned if it matches the given
pattern.

::

only={'file','dir'}


If *only* is specified, it may be either 'file' or 'dir', in which case only
items of the corresponding type are returned.

::

hidden=<bool>

The value of hidden is a boolean that indicates whether items that begin with
'.' are included in the output. If hidden is not specified, hidden items are not
included unless *select* begins with '.'.

Examples::

pyfiles = lsf(select='*.py')
subdirs = lsd()
tmp_mutt = lsf('/tmp/', select='mutt-*')


Paths
-----

Path
~~~~

Create a path from a collection of path segments::

Path(seg, ...)

The segments are combined to form a path. The Path class is actually taken from
the pathlib package.

.. code-block:: python

>>> path = Path('A', 'b', '3')
>>> str(path)
'A/b/3'


Cartesian Product
~~~~~~~~~~~~~~~~~

Create a list of paths by combining from path segments in all combinations::

cartesian_product(seg, ...)

Like with Path(), the components are combined to form a path, but in this case
each component may be a list. The results is the various components are combined
in a Cartesian product to form a list. For example:

.. code-block:: python

>>> paths = cartesian_product(['A', 'B'], ['a', 'b'], ['1', '2'])
>>> for p in paths:
... print(p)
A/a/1
A/a/2
A/b/1
A/b/2
B/a/1
B/a/2
B/b/1
B/b/2


Brace Expand
~~~~~~~~~~~~

Create a list of paths using Bash-like brace expansion::

brace_expand(pattern)

.. code-block:: python

>>> from shlib import brace_expand
>>> paths = brace_expand('python{2.{5..7},3.{2..5}}')

>>> for p in sorted(str(p) for p in paths):
... print(p)
python2.5
python2.6
python2.7
python3.2
python3.3
python3.4
python3.5


Executing Programs
------------------

The following classes and functions are used to execute external programs from
within Python.

Command (Cmd)
~~~~~~~~~~~~~

A class that runs an external program::

Cmd(cmd[, modes][, encoding])

*cmd* may be a list or a string.
*mode* is a string that specifies various options. The options are specified
using a single letter, with upper case enabling the option and lower case
disabling it:

| S, s: Use, or do not use, shell
| O, o: Capture, or do not capture, stdout
| E, e: Capture, or do not capture, stderr
| W, s: Wait, or do not wait, for command to terminate before proceeding

If a letter corresponding to a particular option is not specified, the default
is used for that option. In addition, one of the following may be given, and it
must be given last

| ``*``: accept any output status code
| N: accept any output status code equal to or less than N
| M,N,...: accept status codes M, N, ...

If you do not specify the status code behavior, only 0 is accepted as normal
termination, all other codes will be treated as errors.

For example, to run diff you might use::

diff = Cmd('diff test ref', 'sOEW1')
diff.run()
differences = diff.stdout

Use of O in the modes allows access to stdout, which is needed to access the
differences. Specifying E also allows access to stderr, which in this case is
helpful in case something goes wrong because it allows the error handler to
access the error message generated by diff. Specifying W indicates that run()
should block until diff completes. Specifying 1 indicates that either 0 or 1 are
valid output status codes; any other code output by diff would be treated as an
error.

If you do not indicate that stdout or stderr should be captured, those streams
remain connected to your TTY. You can specify a string to the run() method,
which is fed to the program through stdin. If you don't specify anything the
stdin stream for the program also remains connected to the TTY.

If you indicate that run() should return immediately without out waiting for the
program to exit, then you can use the wait() and kill() methods to manage the
execution. For example::

diff = Cmd(['gvim', '-d', lfile, rfile], 'w')
diff.run()
try:
diff.wait()
except KeyboardInterrupt:
diff.kill()


Run and Sh
~~~~~~~~~~

Run and Sh are subclasses of Cmd. They are the same except that they both run
the program right away (you would not explicitly run the program with the
run()). Run does not use a shell by default where as Sh does.

run, sh, bg, shbg
~~~~~~~~~~~~~~~~~

These are functions that run a program without capturing their output::

run(cmd, stdin=None, accept=0, shell=False)
sh(cmd, stdin=None, accept=0, shell=True)
bg(cmd, stdin=None, shell=False)
shbg(cmd, stdin=None, shell=True)

run and sh block until the program completes, whereas bg and shbg do not. run
and bg do not use a shell by default where as sh and shbg do. accept specifies
the exit status codes that will be accepted without being treated as being an
error. If you specify a simple number, than any code greater than that value is
treated as an error. If you provide a collection of numbers in a tuple or list,
then any code not found in the collection is considered an error.

which
~~~~~

Given a name, a path, and a collection of read, write, or execute flags, this
function returns the locations along the path where a file or directory can be
found with matching flags::

which(name, path=None, flags=os.X_OK)

By default the path is specified by the PATH environment variable and the flags
check whether you have execute permission.