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Write shell scripts in Python

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# pysh

Write shell scripts in Python

## Basic
In pysh, lines that starts with `>` are executed as shell command.
Other lines are evaluated as normal Python script.

for i in xrange(100):
       index = "%02d" % i
       > mv from$index.txt to$index.txt

For example, this pysh script moves from00.txt, from01.txt, …, from99.txt to
to00.txt, to01.txt, …, to99.txt.

Pysh provides the following features

* You can use Python to write shell scripts!
* Lines with `>` prefix are executed as shell command.
* You can use Python variables and expressions in shell command.
* Most of useful shell features like pipe, redirection,
  &&, || and \`cmd\` are supported in pysh.
* You can implement flexible filter and conversion by using
  map and filter commands with Python lambda expression.
  You don't need to learn grep, awk and sed any longer.
* You can write built-in command by Python.
  Also, you can send **Python object** through pipe between built-in commands.

See [Features](#features) section for details.
    
## Install and run

git clone https://github.com/yunabe/pysh.git
    ./pysh/bin/pysh

## pysh command
### Run scripts from files

$ pysh script.pysh

Also, you can write pysh script by adding **#!/path/to/pysh**
(or **/usr/bin/env pysh**) at the top of script files.

#!/path/to/pysh
    # hello.sh
    import os
    > echo Hello ${os.getlogin()}

Run hello.sh

$ ./hello.sh
    Hello yunabe

### Run scripts from stdin

pysh - << 'EOF' arg0 arg1
    import sys
    > echo ${str(sys.argv[1:])}
    EOF

This is useful when you write a *oneliner* in interactive shell like bash and zsh.

### Run scripts from command line args

echo foo bar | pysh -c "`cat << 'EOF'
    import sys
    print repr(sys.stdin.read())
    > echo ${str(sys.argv[1:])}
    EOF`" arg0 arg1
    
This is useful when you define a shell function (e.g. in .bashrc) with pysh.

# <a name="features">Features</a>
## Variable
In pysh, you can use python variable from shell scripts.

x = 3
    y = x * x
    > echo $y     # 9
    > echo $PATH  # os.environment['PATH']

## Python expression
In pysh, you can use any python expression by ${…}.

> echo ${3 + 4}  # 7
    def f(x):
        return x * x
    > echo ${f(10)}  # 100
    > echo ${lambda x: x}

## Pipe
Pipe is supported in pysh.

> echo "foo\nbar" | tac

## Redirection
Redirection is also supported in pysh.

> echo "Hello world" > /dev/null
    > echo "Hello world" >> /dev/null
    > echo "Hello world" 2>&1

## ; && ||

> echo foo; echo bar
    > echo foo && echo bar
    > echo foo || echo bar

## String literal
The format of string literal in pysh is equivalent with
string literal in Python
(In other words, it's different from other shells.)
You can use escape characters like \n, \t.
If you are familiar with Python, you don't need to learn another
string literal format.

> echo "a\nb"

In pysh, variables ($i) and python expression (${…}) in string literals
are evaluated if string literal is double-quoted.
If string literal is single-quoted, pysh does not evaluate $i, ${…} in literals.
    
    > echo "$i"
    > echo '$i'

## map, reduce, filter
map, reduce and filter builtin commands are available in pysh.
These commands read data from pipe and apply "python" function in arg.

### map

> seq 10 | map ${lambda s: int(s) * int(s)}
    1
    4
    9
    ...

### filter

> seq 10 | filter ${lambda s: int(s) % 3 == 0}
    3
    6
    9

### reduce

> seq 10 | reduce ${lambda x, y: int(x) + int(y)}
    55

## Multiline
Like other shell script, you can continue lines
with backslash at the end of line.

> echo foo\
        bar

## Store return code
You can store return code of programs with ->.

> (python -c 'import sys;sys.exit(2)' -> rc0\
        || python -c 'import sys;sys;exit(0)' -> rc1)
    > print rc0, rc1  # 512 0

## Redirect to Python
You can redirect output to Python variable with =>.
The output is stored to Python variable as list
(each line is stored as each element of a list).

> seq 5 | grep -v 3 => out
    print out  # ['1', '2', '4', '5']
    > send ${xrange(5)} | filter ${lambda i: i != 3} => out
    print out  # [0, 1, 2, 4]
    
## Backquote
You can use backquote to use results of commands as command arguments.

> echo `expr 3 + 4`  # 7
    
## Python builtin command
You can write builtin commands in Python.
See [builtin.py](https://github.com/yunabe/pysh/blob/master/pysh/shell/builtin.py)
for details.

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