python-pyl 0.1.0

Python for shell scripting

Harness the full power of Python in your shell scripts and on the command line.

What is pyl?

pyl is a command line tool that let’s you write terse but readable shell one-liners using Python. It does this by introducing a few powerful syntax extensions, described below.

Why?

Python has a super extensive standard library, making it the ultimate shell-scripting toolbox. The problem is that, while very concise compared to other languages, running Python snippets from within shell scripts is quite clunky. Consider the following code that base64-encodes each line of input:

$ ls | python -c $'import base64, sys\nfor l in sys.stdin: print(base64.b64encode(l.encode()).decode())'
TElDRU5TRQo=
UkVBRE1FLnJzdAo=
cHlwcm9qZWN0LnRvbWwK
c3JjCg==

The biggest problem with inline Python is whitespace: Python requires newlines and indentation, and it’s not convenient to include those in strings on the command line.

With pyl, the above command becomes:

$ ls | pyl 'for l in sys::stdin: { base64::b64encode(l.encode()).decode() }'
TElDRU5TRQo=
UkVBRE1FLnJzdAo=
cHlwcm9qZWN0LnRvbWwK
c3JjCg==

The Solution

pyl introduces a number of syntax extensions that, together, make it easy to write readable shell one-lines that take full advantage of everything Python has to offer:

Braces

Curly braces that appear immediately after a colon become indentation.

Example:

for i in range(3): { for j in range(4): { print(i * j); } }

is equivalent to

for i in range(3):
    for j in range(4):
        print(i * j)

Line splitting at ;

Lines are split at semicolons.

In normal Python, statements like if and for need to appear on their own line. with pyl you can just use a semicolon:

Example:

import sys; for arg in sys.argv: { print(arg); }

is equivalent to

import sys
for arg in sys.argv:
    print(arg)

Implicit print

If a block (either top-level or indented) ends without a semicolon, the last line is automatically printed (unless the block ends in another block).

In fact, the whole line is passed as-is to print, so you can pass keyword arguments like sep.

Example:

for i in range(10): { i, end='.' }

is equivalent to

for i in range(10):
    print(i, end='.')

Inline-import

The :: operator can be used to access members of modules without explicitly importing them.

Example:

urllib.parse::quote('hello world')

is equivalent to

print(__import__('urllib.parse').parse.quote('hello world'))

Environment variables

Environment variables can be accessed with $NAME.

Example:

$HOME

is equivalent to

print(__import__('os').environ['HOME'])

Command line arguments

Command line arguments can be accessed with $INDEX where INDEX is a number.

Example:

$1

is equivalent to

print(__import__('sys').argv[1])