spice up your tail minus effs with greenbar

I've been missing this tool for a while now. The original "greenbar" was in written in awk, probably by my friend Mark S. It took input and inverted the text of every other line (like greenbar printer paper). It made watching log files scroll up your terminal much easier to parse.

Here's my python version which has one new feature. It can be given a string argument in which case it will only highlight lines in its input that contain that string.

#!/usr/bin/python -u

import sys

REG = "\x1b[0m"
INV = "\x1b[7m"

try:
   pat = sys.argv[1]
except IndexError:
   pat = None

i = 0
while 1:
     line = sys.stdin.readline()
   if not line:
       break
   if pat:
       if pat in line:
           print INV, line,
       else:
           print REG, line,
   else:
       if i % 2 == 0:
           print INV, line,
       else:
           print REG, line,
   i = i + 1
if i:
   print REG

It's important to use unbuffered I/O, thus the "-u" flag to python is used along with sys.stdin.readline().