Grep and Python


Question

I need a way of searching a file using grep via a regular expression from the Unix command line. For example when I type in the command line:

python pythonfile.py 'RE' 'file-to-be-searched'

I need the regular expression 'RE' to be searched in the file and print out the matching lines.

Here's the code I have:

import re
import sys

search_term = sys.argv[1]
f = sys.argv[2]

for line in open(f, 'r'):
    if re.search(search_term, line):
        print line,
        if line == None:
            print 'no matches found'

But when I enter a word which isn't present, no matches found doesn't print

1
64
1/31/2017 1:23:18 AM

The natural question is why not just use grep?! But assuming you can't...

import re
import sys

file = open(sys.argv[2], "r")

for line in file:
     if re.search(sys.argv[1], line):
         print line,

Things to note:

  • search instead of match to find anywhere in string
  • comma (,) after print removes carriage return (line will have one)
  • argv includes python file name, so variables need to start at 1

This doesn't handle multiple arguments (like grep does) or expand wildcards (like the Unix shell would). If you wanted this functionality you could get it using the following:

import re
import sys
import glob

for arg in sys.argv[2:]:
    for file in glob.iglob(arg):
        for line in open(file, 'r'):
            if re.search(sys.argv[1], line):
                print line,
74
1/31/2017 1:24:08 AM

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