.. getthecode:: sysadmin.py
    :language: python3
    :hidden:

=======================
 System Administration
=======================

This page contains snippets for system administration tasks.

See also

* https://docs.python.org/3/library/pathlib.html



.. code-block:: py3

    import os # os tools
    import re # regexp tools
    import subprocess # subprocesses tools
    import tempfile # temporary file and directory tools
    
    from Tools import *
    
Note: Temporary file and directory are addressed first so as to define a temporary file hierarchy
context manager used afterwards in this page.

Temporary File and Directory
----------------------------

Reference: https://docs.python.org/3/library/tempfile.html


.. code-block:: py3

    with tempfile.TemporaryFile() as fh:
        fh.write(b'Hello world!')
        fh.seek(0)
        print(fh.read())

.. code-block:: none

    b'Hello world!'
    

.. code-block:: py3

    with tempfile.TemporaryDirectory() as tmp_directory:
        print('Created temporary directory', tmp_directory)

.. code-block:: none

    Created temporary directory /tmp/tmpvq5p6by8
    
Create a filesystem hierarchy


.. code-block:: py3

    with tempfile.TemporaryDirectory() as tmp_directory:
        print('Created temporary directory', tmp_directory)
        for directory in ('.', 'subdir'):
            directory_path = os.path.join(tmp_directory, directory)
            if not os.path.exists(directory_path):
                os.mkdir(directory_path)
            for name in ('file1.txt', 'file.txt'):
                path = os.path.join(directory_path, name)
                with open(path, 'w') as fh:
                    fh.write('...')
    
Using a context manager


.. code-block:: py3

    class TemporaryFileHierarchy:
    
        def __init__(self, *args, **kwargs):
    
            self._tmp_directory = tempfile.TemporaryDirectory()
            print('Created temporary directory', tmp_directory)
    
            self._chdir = kwargs.get('chdir', False)
    
            for directory in ('.', 'subdir'):
                directory_path = os.path.join(self._tmp_directory.name, directory)
                if not os.path.exists(directory_path):
                    os.mkdir(directory_path)
                for name in ('file1', 'file2'):
                    path = os.path.join(directory_path, name)
                    with open(path, 'w') as fh:
                        fh.write(kwargs.get(name, '...'))
    
    
        def __enter__(self):
            path = self._tmp_directory.name
            if self._chdir:
                os.chdir(path)
            return path
    
    
        def __exit__(self, exc_type, exc_value, traceback):
            # self._tmp_directory.cleanup()
            pass
    

Filesystem Snippets
-------------------

Reference: https://docs.python.org/3/library/os.path.html#module-os.path


.. code-block:: py3

    with TemporaryFileHierarchy() as tmp_directory:
    
        # change current working directory
        os.chdir(tmp_directory)
        print('curent directory is now:', os.getcwd())
    
        abs_path = os.path.join(tmp_directory, 'subdir', 'file1') + '.txt'
        pretty_print((
            os.path.dirname(abs_path),
            os.path.basename(abs_path),
            os.path.splitext(abs_path),
        ))
        abs_path = os.path.join(tmp_directory, 'subdir', '..', 'file1')
        pretty_print((
            abs_path,
            os.path.realpath(abs_path), # remove .. and symlinks
        ))
        abs_path = os.path.join('.', 'subdir', 'file1')
        pretty_print((
            abs_path,
            os.path.abspath(abs_path),
        ))

.. code-block:: none

    Created temporary directory /tmp/tmp1q225o3t
    curent directory is now: /tmp/tmp6v7i6fgj
        (   '/tmp/tmp6v7i6fgj/subdir',
            'file1.txt',
            (   '/tmp/tmp6v7i6fgj/subdir/file1',
                '.txt'))
        (   '/tmp/tmp6v7i6fgj/subdir/../file1',
            '/tmp/tmp6v7i6fgj/file1')
        (   './subdir/file1',
            '/tmp/tmp6v7i6fgj/subdir/file1')
    

File Permission
---------------

Reference: https://docs.python.org/3/library/os.html


.. code-block:: py3

    with TemporaryFileHierarchy(chdir=True) as tmp_directory:
    
        for permission in (
                os.F_OK,
                os.R_OK,
                os.W_OK,
                os.X_OK,
        ):
            print('permission {}: {}'.format(permission, os.access("file1", permission)))

.. code-block:: none

    Created temporary directory /tmp/tmp6v7i6fgj
    permission 0: True
    permission 4: True
    permission 2: True
    permission 1: False
    

Walk recursively on the filesystem (find)
-----------------------------------------
This snippet replaces the *find* command:

Reference: https://docs.python.org/3/library/os.html#os.walk


.. code-block:: py3

    with TemporaryFileHierarchy() as tmp_directory:
    
        for path, directories, files in os.walk(tmp_directory):
            print(path, directories, files)
            for filename in files:
                print(os.path.join(path, filename))

.. code-block:: none

    Created temporary directory /tmp/tmpwv0rneo9
    /tmp/tmpcgdguli8 ['subdir'] ['file2', 'file1']
    /tmp/tmpcgdguli8/file2
    /tmp/tmpcgdguli8/file1
    /tmp/tmpcgdguli8/subdir [] ['file2', 'file1']
    /tmp/tmpcgdguli8/subdir/file2
    /tmp/tmpcgdguli8/subdir/file1
    
PEP 471 – os.scandir() function – a better and faster directory iterator


.. code-block:: py3

    with TemporaryFileHierarchy() as tmp_directory:
    
        for entry in os.scandir(tmp_directory):
            print(entry, entry.is_file(), entry.name)

.. code-block:: none

    Created temporary directory /tmp/tmpcgdguli8
    <DirEntry 'subdir'> False subdir
    <DirEntry 'file2'> True file2
    <DirEntry 'file1'> True file1
    

pattern Matching/Substitution (grep, sed)
-----------------------------------------
This snippet replaces the *grep* and *sed* commands:


.. code-block:: py3

    file1_content = '''
    Hello John,
    It's a beautiful day!
    Cheers,
    '''
    
    with TemporaryFileHierarchy(file1=file1_content) as tmp_directory:
    
        for path, directories, files in os.walk(tmp_directory):
            for filename in files:
                abs_path = os.path.join(path, filename)
                matched = False
                with open(abs_path, 'r') as fh:
                    for line in fh.readlines():
                        # line = line.rstrip() # strip leading spaces and \n
                        if re.match('.*John.*', line):
                            print(abs_path, ':', line.rstrip())
                            matched = True
                if matched:
                    # get content
                    with open(abs_path, 'r') as fh:
                        content = fh.read()
                    # update content
                    content = content.replace('John', 'Paul')
                    # write file inplace
                    with open(abs_path, 'w') as fh:
                        fh.write(content)
                    # new content is
                    with open(abs_path, 'r') as fh:
                        print(fh.read())

.. code-block:: none

    Created temporary directory /tmp/tmpvbivcgh3
    /tmp/tmp4c5enstk/file1 : Hello John,
    
    Hello Paul,
    It's a beautiful day!
    Cheers,
    
    /tmp/tmp4c5enstk/subdir/file1 : Hello John,
    
    Hello Paul,
    It's a beautiful day!
    Cheers,
    
    

Execute subprocesses
--------------------

Reference: https://docs.python.org/3/library/subprocess.html


.. code-block:: py3

    file1_content = '''
    Hello John,
    It's a beautiful day!
    Cheers,
    '''
    
    with TemporaryFileHierarchy(file1=file1_content, chdir=True) as tmp_directory:
    
        # subprocess.call
        rc = subprocess.call(('grep', '-i', 'john', 'file1'))
        print('grep john:', rc == 0)
    
        rc = subprocess.call(('grep', '-i', 'paul', 'file1'))
        print('grep paul:', rc == 0)
    
        try:
            # subprocess.check_call
            subprocess.check_call(('grep', '-i', 'john', 'file1'))
            print('will fail')
            subprocess.check_call(('grep', '-i', 'paul', 'file1'))
        except subprocess.CalledProcessError:
            print('grep failed')
    
        # subprocess.check_output
        output = subprocess.check_output(('cat', 'file1'))
        print(output.decode('utf-8'))

.. code-block:: none

    Created temporary directory /tmp/tmp4c5enstk
    grep john: True
    grep paul: False
    will fail
    grep failed
    
    Hello John,
    It's a beautiful day!
    Cheers,