ShLib - 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. Furthermore, most of the features of pathlib are implemented as pathlib methods, so you must convert your strings to paths before you can use them. ShLib is equally comfortable with strings as with paths.

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, mkdir, and cd. 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 Python2.7 or Python3.3 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:

>>> from shlib import *
>>> 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 = to_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 = to_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 = to_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.

>>> from shlib import *
>>> 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 = to_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.

>>> 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)

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.

Change Directory (cd)

Change to an existing directory:

cd(path)

Makes path the current working directory.

May also be used in a with block:

with cd(path):
    cwd()

The working directory returns to its original value upon leaving the with block.

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

to_path

Create a path from a collection of path segments:

p = to_path(seg, ...)

The segments are combined to form a path. Expands a leading ~. Returns a pathlib path. It is generally not necessary to apply to_path() to paths being given to the shlib functions, but using it gives you access to all of the various pathlib methods for the path.

>>> path = to_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 to_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:

>>> 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)
>>> paths = brace_expand('python{2.{5..7},3.{2..6}}')

>>> 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
python3.6

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:

>>> import sys, textwrap
>>> ref = textwrap.dedent('''
...     line1
...     line2
...     line3
... ''').strip()
>>> test = textwrap.dedent('''
...     line1
...     line2
... ''').strip()

>>> ref_bytes_written = to_path('./ref').write_text(ref)
>>> test_bytes_written = to_path('./test').write_text(test)

>>> cat = Cmd(['cat', 'test'], 'sOeW')
>>> cat.run()
0

>>> print(cat.stdout)
line1
line2

>>> diff = Cmd('diff test ref', 'sOEW1')
>>> status = diff.run()
>>> status
1

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 whereas Sh does.

>>> echo = Run('echo hello world > helloworld', 'SoeW')
>>> echo.status
0
>>> cat = Run(['cat', 'helloworld'], 'sOeW')
>>> cat.status
0
>>> print(cat.stdout)
hello world

run, sh, bg, shbg

These are functions that run a program without capturing its 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.