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 pythonfi         


        

Answer 1

Adapted from a grep in python.

Accepts a list of filenames via [2:], does no exception handling:

#!/usr/bin/env python
import re, sys, os

for f in filter(os.path.isfile, sys.argv[2:]):
    for line in open(f).readlines():
        if re.match(sys.argv[1], line):
            print line

sys.argv[1] resp sys.argv[2:] works, if you run it as an standalone executable, meaning

chmod +x

first

Answer 2

You might be interested in pyp. Citing my other answer:

"The Pyed Piper", or pyp, is a linux command line text manipulation tool similar to awk or sed, but which uses standard python string and list methods as well as custom functions evolved to generate fast results in an intense production environment.

Answer 3

1. use sys.argv to get the command-line parameters
2. use open(), read() to manipulate file
3. use the Python re module to match lines

Answer 4

You can use python-textops3 :

from textops import *

print('\n'.join(cat(f) | grep(search_term)))

with python-textops3 you can use unix-like commands with pipes

Answer 5

Concise and memory efficient:

#!/usr/bin/env python
# file: grep.py
import re, sys

map(sys.stdout.write,(l for l in sys.stdin if re.search(sys.argv[1],l)))

It works like egrep (without too much error handling), e.g.:

cat input-file | grep.py "RE"

And here is the one-liner:

cat input-file | python -c "import re,sys;map(sys.stdout.write,(l for l in sys.stdin if re.search(sys.argv[1],l)))" "RE"

Answer 6

The real problem is that the variable line always has a value. The test for "no matches found" is whether there is a match so the code "if line == None:" should be replaced with "else:"