# Simple grep in Python


```python
#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""Various text processing utilities.

Majority of these are intended for working with files but will work on any
string iterables as well.
"""

import re


def has_line(items, line):
    """Check if a line exists."""
    if not line.endswith('\n'):
        match = line + '\n'
    else:
        match = line
    return match in items


def has_pattern(items, pattern, ignore_case=False):
    """Check if an item matching pattern exists."""
    regexp = re.compile(pattern, flags=ignore_case and re.I)
    for item in items:
        match = regexp.search(item)
        if match:
            return True
    else:
        return False


def grep(items, pattern, ignore_case=False):
    """Get a list of all items matching regular expression."""
    regexp = re.compile(pattern, flags=ignore_case and re.I)
    matches = []
    for item in items:
        match = regexp.search(item)
        if match:
            matches.append(match.string)
    return matches


def igrep(items, pattern, ignore_case=False):
    """Iterate over all items matching regular expression."""
    regexp = re.compile(pattern, flags=ignore_case and re.I)
    return filter(regexp.search, items)


def cli(in_file, pattern, ignore_case=False, *args, **kwargs):
    """CLI entrypoint for `igrep`."""
    matches = igrep(in_file, pattern, ignore_case)
    # sort of a hack to check if iterator has at least one item
    try:
        first = next(matches)
        print(first, end='')
    except StopIteration:
        return 1
    for match in matches:
        print(match, end='')
    return 0


if __name__ == '__main__':
    import argparse
    import sys
    parser = argparse.ArgumentParser()
    parser.add_argument(
            'pattern',
            metavar='PATTERN',
            help='pattern to search for')
    parser.add_argument(
            'in_file',
            nargs='?',
            metavar='FILE',
            default=sys.stdin,
            type=argparse.FileType('r'),
            help='file to search in')
    parser.add_argument(
            '-i',
            '--ignore-case',
            action='store_true',
            help='case insensitive match')
    args = parser.parse_args()
    sys.exit(cli(**vars(args)))
```