shalchemy 0.1.0

A shell scripting toolkit for Python

Shalchemy

For when you get tired of Python and sh and want something in between.

from shalchemy import sh, run
from shalchemy.bin import cat, curl, grep

if cat('/etc/hosts') | grep('localhost'):
    run(curl('example.com') > 'file.txt')
    for line in cat('file.txt'):
        print(line)
    run(shalchemy.bin.rm('file.txt'))

Note that none of these are Python functions. We just call the system binaries using subprocess and do an unhealthy amount of magic to tie everything together.

Installation

$> pip install shalchemy

Tutorial

There are only three things you need to care about. shalchemy.sh, shalchemy.run, and shalchemy.bin.

You create expressions by chaining shalchemy.sh instances together.

import shalchemy
ps_aux = shalchemy.sh('ps', 'aux')
grep = shalchemy.sh('grep', 'python')
piped_expression = ps_aux | grep

These expressions on their own don’t actively run the underlying system commands. They are evaluated in these three circumstances:

• They are passed to shalchemy.run

• They are converted to a bool, str, or int

• They are iterated over

During the evaluation phase, subprocesses are created, files are opened, and things are piped together with Linux magic. The Python process blocks until everything is finished. Once all the processes are done, things are cleaned up, and the correct data type is provided to the user.

Pipes and Redirects

shalchemy expressions support pipes | and redirects (<, <<, >, >>) for stdout.

To redirect stderr, there is the stderr method.

from shalchemy import sh, run
from sqlalchemy.bin import rm
run(rm('nonexistent_file').stderr('&1') > 'log.txt'))
run(rm('nonexistent_file2').stderr('somefile') >> 'log.txt'))

Sadly, Python doesn’t support the 2> operation.

Arguments

shalchemy.sh is used to create expressions. Calling it creates an internal CommandExpression. These CommandExpressions hold arguments and can curry them. You can also access their properties to naturally generate curried expressions for subcommands. As a result, these four different python lines will create the same CommandExpression:

from shalchemy import sh
from shalchemy.bin import git
expr1 = sh('git show .')  # Special
expr2 = sh('git', 'show', '.')
expr3 = sh(['git', 'show', '.'])
expr4 = git('show', '.')
expr5 = git.show('.')

There is something special about expr1 that should be noted. If sh (or any CommandExpression) receives a single string as the only argument, it will assume that you wanted to type a sh-compatible string and it’ll automatically tokenize it for you using shlex.

In other words, sh('git show .') will create the Command sh(['git', 'show', '.']). If you don’t like the automatic tokenization, you can explicitly provide a list with a single string inside``sh([‘git show .’])``. Note that this second version will attempt to search your $PATH for a binary named git\ show\ . which is almost always not what anybody wants. Just a small warning for this special automatic tokenization thing that might become a gotcha one day.

shalchemy.bin

The shalchemy.bin module is a magic module that wraps whatever you want to import in shalchemy.sh in a straightforward way. Importing grep from sqlalchemy.bin will just give you the result of sh('grep')