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Small tool to interact with shell pipes

tag: 0.3

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README.rst

Chut

Chut is a small tool to help you to interact with shell pipes and commands.

Basically it will help to write some shell script in python

This is more like a toy than a real tool but... It may be useful sometimes.

It's tested with py2.6+ and py3.2+:

https://secure.travis-ci.org/gawel/chut.png

Installation

Using pip:

$ pip install chut

Usage

Import the shell:

>>> from chut import ch

Then run what you want:

>>> print(ch.cat('README.rst') | ch.grep('Chut') | ch.head("-n1"))
Chut

When I said what you want it's mean that ch.whatyouwant will call a binary named whatyouwant

Let's check if an error occurred with whatyouwant:

>>> str(ch.whatyouwant()) # doctest: +ELLIPSIS
Traceback (most recent call last):
...
OSError: whatyouwant

About imports

You can import ch and sudo:

>>> from chut import ch, sudo

But you can also import some specific commands:

>>> from chut import cat, grep, gzip, gunzip
>>> from chut.sudo import ifconfig

The pipe context manager

An error can occur if the binary exist:

>>> cmd = ch.cat('whatyouwant')
>>> output = str(cmd)
>>> output.succeeded
False
>>> print(output.stderr)
cat: whatyouwant: No such file or directory

A context manager can help you to check for some errors:

>>> with ch.pipe(cat('fff') | grep('fff')) as p: # doctest: +ELLIPSIS
...    print(p)
Traceback (most recent call last):
...
OSError: cat: fff: No such file or directory

Basically it checks return codes at the end of the pipe

Use predefined pipe

Define an pipe:

>>> chut = cat('README.rst') | grep('chut')

And use it:

>>> chut | ch.head('-n1')
'cat README.rst | grep chut | head -n1'

The original defined pipe stay as this (everything is copied):

>>> chut
'cat README.rst | grep chut'

You can also extract parts of the pipe using slices:

>>> chut[1:]
'grep chut'

SSH

The ssh command take a host first and is gziped by default:

>>> from chut import ssh
>>> srv1 = ssh('gawel@srv')
>>> srv1.ls('~')
'ssh gawel@srv ls ~'

For example you can backup your mysql database locally:

>>> srv1.mysqldump('db | gzip') | gzip
"ssh gawel@srv 'mysqldump db | gzip' | gzip"

Or on another server:

>>> srv2 = ssh('gawel@srv2')
>>> srv1(ch.mysqldump('db') | gzip | srv2('gunzip > ~/backup.db'))
'ssh gawel@srv "mysqldump db | gzip | ssh gawel@srv2 \'gunzip > ~/backup.db\'"'

You can use your ssh instance to get some remote file:

>>> ch.rsync(srv1.join('~/p0rn'), '.', pipe=True)
'rsync gawel@srv:~/p0rn .'

Sudo

You can for sure use sudo:

>>> from chut import sudo
>>> sudo.ls() | sudo.grep('chut')
'sudo -s ls | sudo -s grep chut'

Sudo wont work with ssh except if it does not require a password

Testing

You can use the test command:

>>> from chut import test

>>> # test -f chut.py
>>> bool(test.f('chut.py'))
True

>>> # test -x chut.py
>>> if test.x('chut.py'):
...     print('Chut.py is executable')

Use python !!

You can use some python code ad the end of the pipe (and only at the end):

>>> @ch.wraps
... def check_chut(stdin):
...     for line in stdin:
...         if line.startswith(b'Chut'):
...             yield b'Chut rocks!\n'
...             break

>>> with ch.pipe(cat('README.rst') | check_chut) as cmd:
...     for line in cmd:
...         print(line)
Chut rocks!
<BLANKLINE>

Input

You can use a python string as input:

>>> print(ch.stdin(b'gawel\nfoo') | grep('gawel'))
gawel

The input can be a file but the file is not streamed by stdin(). Notice that the file must be open in binary mode (rb):

>>> print(ch.stdin(open('README.rst', 'rb'))
...               | grep('Chut') | ch.head('-n1'))
Chut

Output

You can get the output as string:

>>> output = str(cat('README.rst') | check_chut)
>>> output = (cat('README.rst') | check_chut)()

As an iterator (iterate over each lines of the output):

>>> chut_stdout = cat('README.rst') | check_chut

And can use some redirection:

>>> ret = chut_stdout > 'chut.txt'
>>> ret.succeeded
True
>>> print(cat('chut.txt'))
Chut rocks!

>>> ret = chut_stdout >> 'chut.txt'
>>> ret.succeeded
True
>>> print(cat('chut.txt'))
Chut rocks!
Chut rocks!

Parentheses are needed with >> (due to the way the python operator work):

cat('README.rst') | grep >> 'chut.txt' # wont work
(cat('README.rst') | grep) >> 'chut.txt' # work
>>> ch.rm('-f chut.txt')
'rm -f chut.txt'

Exceptions

The cd command use python os.chdir()

Some commands do not use a pipe by default. This mean that they are executed immediately:

>>> ch.not_piped
['cp', 'mkdir', 'mv', 'rm', 'rsync', 'scp', 'touch']

By default a command is piped. But you can avoid this:

>>> ch.ls(pipe=False)
'ls'

By default a command do not launch a shell. But if you need you can use one:

>>> ch.ls(shell=True)
'ls'

>>> ch.ls(sh=True)
'ls'

Debugging

You can print your pipe:

>>> print(repr(cat('README.txt') | check_chut))
'cat README.txt | check_chut()'

You can also activate logging:

>>> import logging
>>> logging.basicConfig(level=logging.DEBUG)
>>> log = logging.getLogger('chut')
>>> # set level/handler

Cheers.

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