Use filter commands to process text

==Simple filter example==
Following is a Python program to sort the words on each line of standard input (each line is separately sorted).
<pre>
# File sortwords.py
from sys import stdin
for line in stdin:
    print ' '.join(sorted(line.split()))
</pre>

A file you are editing in Vim may include the following text:
<pre>
this is a line with some words
words on each line will be sorted
fried banana and cream
</pre>

Use this procedure to filter the text:
*Press <code>V</code> on the first line, then <code>jj</code> to select three lines.
*Type <code>!python sortwords.py</code> and press Enter.
The lines are replaced with the result from running the program:
<pre>
a is line some this with words
be each line on sorted will words
and banana cream fried
</pre>