backquotes 0.1.0

shell command invocation with backquotes, like Perl, Ruby.

Introduction

backquotes brings (Perl / Ruby)’s shell invocation syntax to Python.

Since backquotes is an experimental module, using it in a serious program is not recommended.

Syntax

Firstly, do not forget to import backquotes module.

import backquotes

Basic

You can use similar syntax to Perl / Ruby.

import backquotes
print(`date`)

Pipes and redirections

Yes, you can use pipes, redirections too.

import backquotes
print(`ls | tr [a-z] [A-Z]`.splitlines())

Local variables substitution

To bring local variables in Python code to shell command, use Perl-like variables substitution.

import backquotes
spam = 'spam'
print(`echo $spam`)

$$ is replaced with a literal $.

import backquotes
print(`echo $$PATH`)

Usage

Runtime-preprocessing

You can use runtime-preprocessing only in Python 2. This works transparently whenever you import backquotes.

Warning

Python 3 raises SyntaxError on a backquote character before evaluate the first line. So you CANNOT use runtime-preprocessing.

#!/usr/bin/env python
import backquotes
print(`date`)

Save the above code as date.py, and run it as usual.

python date.py

You will see the result of date command.

Runtime-preprocessing sometimes causes SyntaxError before preprocessing starts, especially with complex commands invocation. You can avoid this error by using single-quotes just inside the backquotes.

print(`'for file in *; do echo $file; done'`)

Execute backquotes module

Run python with -m backquotes option to invoke backquotes as a script. backquotes compiles a plain Python code and execute it.

Note

This works both in Python 2 / 3.

python -m backquotes date.py

You can pass arguments to the script like this.

python -m backquotes date.py 2015 10 31

Preprocess Python code

Run python with -m backquotes -E option to only preprocess the given source file and print the result to stdout.

Warning

Preprocessed python code is almost the same as the original code semantically, but whitespaces may be moved by the preprocessor.

Note

This works both in Python 2 / 3.

mkdir dist
python -m backquotes -E date.py > dist/date.py
python dist/date.py

Restrictions

• backquotes does not work in Python REPL. Importing it in REPL causes warnings.

• A module which imports backquotes does not work when it is imported by another module.

Install

pip install backquotes

or

git clone https://github.com/manicmaniac/backquotes.git
cd backquotes
python setup.py install

or

wget https://raw.githubusercontent.com/manicmaniac/backquotes/master/backquotes.py