exercise11_1.py

"""
Exercise  11.1: Write a simple program to simulate the operation of the grep
command on Unix. Ask the user to enter a regular expression and count the
number of lines that matched the regular expression:

$ python grep.py
Enter a regular expression: ^Author
mbox.txt had 1798 lines that matched ^Author

$ python grep.py
Enter a regular expression: ^X-
mbox.txt had 14368 lines that matched ^X-

$ python grep.py
Enter a regular expression: java$
mbox.txt had 4218 lines that matched java$

Python for Everybody: Exploring Data Using Python 3
by Charles R. Severance

Solution by Jamison Lahman, June 4, 2017
"""
import re

input_exp = str(input('Enter a regular expression: '))
reg_exp = str(input_exp)                #Regular Expressions are strings
fname = 'mbox.txt'
fhand = open(fname)
count = 0

for line in fhand:
    line = line.rstrip()
    if re.findall(reg_exp,line) != []:  #Only counts if something was found
        count += 1
        
print(fname,'had ',count,'lines that matched',reg_exp)