Problem 3.2

Grep Command

Implement Unix command grep in Python.

Write a program grep.py that takes a pattern and a file as command-line arguments and print all the lines in the file that contain that pattern.

The pattern could be any text and there is no need to support regular expressions.

$ cat files/zen.txt
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!

$ python grep.py never files/zen.txt
Errors should never pass silently.
Now is better than never.
Although never is often better than *right* now.

$ grep the files/zen.txt
Special cases aren't special enough to break the rules.
In the face of ambiguity, refuse the temptation to guess.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.

Solution

import sys

pat = sys.argv[1]
filename = sys.argv[2]

for line in open(filename):
    if pat in line:
        print(line, end="")