helper.py

from contextlib import contextmanager
import subprocess
import re
import sys
import time
import curses

# usage: 
# cmd = ['ls', '-l']
# pattern = re.compile('beans')
# with watch_until(cmd, pattern) as w:
#     # do stuff

@contextmanager
def watch_output(cmd, **kwargs):
    if 'stop_regex' not in kwargs:
        raise ValueError('stop_regex is required')
    if 'interval' in kwargs:
        interval = kwargs['interval']
        del kwargs['interval']
    else:
        interval = 1

    stop_regex = kwargs['stop_regex']
    del kwargs['stop_regex']

    def loop(stdscr):
        # reset colors
        curses.use_default_colors()
        while True:
            stdscr.erase()
            out = subprocess.check_output(cmd, **kwargs)
            if stop_regex.search(out):
                return out

            lines = out.decode('utf-8').splitlines()
            status_widget = "Every {}s: {}".format(interval, ' '.join(cmd))
            time_widget = time.ctime()
            padding = ' ' * (curses.COLS - len(status_widget) - len(time_widget))
            stdscr.addstr(0, 0, status_widget + padding + time_widget)
            for i, line in enumerate(lines[-curses.LINES:]):
                stdscr.addstr(i+2, 0, line + "\n")
            stdscr.refresh()
            time.sleep(interval)
    yield curses.wrapper(loop)

if __name__ == '__main__':
    w = watch_output(
        ['ls', '-l'],
        stop_regex=re.compile('beans'),
        interval=1
    )
    with w as out:
        print('found beans')