1  #! /usr/bin/env python3
       2  
       3  """Reverse grep.
       4  
       5  Usage: rgrep [-i] pattern file
       6  """
       7  
       8  import sys
       9  import re
      10  import getopt
      11  
      12  
      13  def main():
      14      bufsize = 64 * 1024
      15      reflags = 0
      16      opts, args = getopt.getopt(sys.argv[1:], "i")
      17      for o, a in opts:
      18          if o == '-i':
      19              reflags = reflags | re.IGNORECASE
      20      if len(args) < 2:
      21          usage("not enough arguments")
      22      if len(args) > 2:
      23          usage("exactly one file argument required")
      24      pattern, filename = args
      25      try:
      26          prog = re.compile(pattern, reflags)
      27      except re.error as msg:
      28          usage("error in regular expression: %s" % msg)
      29      try:
      30          f = open(filename)
      31      except IOError as msg:
      32          usage("can't open %r: %s" % (filename, msg), 1)
      33      with f:
      34          f.seek(0, 2)
      35          pos = f.tell()
      36          leftover = None
      37          while pos > 0:
      38              size = min(pos, bufsize)
      39              pos = pos - size
      40              f.seek(pos)
      41              buffer = f.read(size)
      42              lines = buffer.split("\n")
      43              del buffer
      44              if leftover is None:
      45                  if not lines[-1]:
      46                      del lines[-1]
      47              else:
      48                  lines[-1] = lines[-1] + leftover
      49              if pos > 0:
      50                  leftover = lines[0]
      51                  del lines[0]
      52              else:
      53                  leftover = None
      54              for line in reversed(lines):
      55                  if prog.search(line):
      56                      print(line)
      57  
      58  
      59  def usage(msg, code=2):
      60      sys.stdout = sys.stderr
      61      print(msg)
      62      print(__doc__)
      63      sys.exit(code)
      64  
      65  
      66  if __name__ == '__main__':
      67      main()