Filter all unchanged and all only-comment lines from a diff-output.

diff-filter.py

#!/usr/bin/python
"""
Filter all unchanged and all only-comment lines from a diff-output.

and be more terse.
"""

import sys
import re

only_space_before_comment = re.compile(r'^[+-]\s*#')
empty_diff_line = re.compile(r'^[+-]\s*$')

state = 0
save_line = None
for line in sys.stdin.readlines():
    # ignore the header (following after a `diff ...` line) like:
    #   index fa1e684..32e2c2b 100755
    #   --- a/contrib/livestatus/splitlivelogs.py
    #   +++ b/contrib/livestatus/splitlivelogs.py
    if state == 1 and line.startswith('index '):
        state += 1
        continue
    elif state == 2 and line.startswith('--- '):
        save_line = line # print this line later if there is further output
        state += 1
        continue
    elif state == 3 and line.startswith('+++ '):
        state = 0
        continue
    
    # header lines should have filtered by the code obove, so just
    # reset state
    state = 0

    if line.startswith('diff '):
        #save_line = line -- print the '--- ' line instead (more terse)
        # expect the header to come next
        state = 1
        continue
    elif line.startswith('@@ ') and ' @@' in line:
        # ignore position lines
        continue
    elif line.startswith(' '):
        # ignore context lines
        continue
    elif only_space_before_comment.match(line):
        continue
    elif empty_diff_line.match(line):
        continue
    elif line.startswith('+') or line.startswith('-'):
        # diff add line
        # only strip add lines, so we can see what has been removed
        line = line.rsplit('#',1)[0] # remove comment (from the right)
        line = line.rstrip('#') # remove further trailing hash signs
        ## # to be used in config files
        ## line = line.rsplit(';',1)[0] # remove comment (from the right)
        ## line = line.rstrip(';') # remove further trailing hash signs
        line = line.rstrip() + '\n' # re-append stripped newline

    if save_line:
        print
        sys.stdout.write(save_line)
        save_line = None
    sys.stdout.write(line)