New tool: reverse grep (greps from the end). Uses a fairly efficient

strategy to read from the end of the file.

Tools/scripts/rgrep.py

+#! /usr/bin/env python
+
+"""Reverse grep.
+
+Usage: rgrep [-i] pattern file
+"""
+
+import sys
+import re
+import string
+import getopt
+
+def main():
+    bufsize = 64*1024
+    reflags = 0
+    opts, args = getopt.getopt(sys.argv[1:], "i")
+    for o, a in opts:
+        if o == '-i':
+            reflags = reflags | re.IGNORECASE
+    if len(args) < 2:
+        usage("not enough arguments")
+    if len(args) > 2:
+        usage("exactly one file argument required")
+    pattern, filename = args
+    try:
+        prog = re.compile(pattern, reflags)
+    except re.error, msg:
+        usage("error in regular expression: %s" % str(msg))
+    try:
+        f = open(filename)
+    except IOError, msg:
+        usage("can't open %s: %s" % (repr(filename), str(msg)), 1)
+    f.seek(0, 2)
+    pos = f.tell()
+    leftover = None
+    while pos > 0:
+        size = min(pos, bufsize)
+        pos = pos - size
+        f.seek(pos)
+        buffer = f.read(size)
+        lines = string.split(buffer, "\n")
+        del buffer
+        if leftover is None:
+            if not lines[-1]:
+                del lines[-1]
+        else:
+            lines[-1] = lines[-1] + leftover
+        if pos > 0:
+            leftover = lines[0]
+            del lines[0]
+        else:
+            leftover = None
+        lines.reverse()
+        for line in lines:
+            if prog.search(line):
+                print line
+
+def usage(msg, code=2):
+    sys.stdout = sys.stderr
+    print msg
+    print __doc__
+    sys.exit(code)
+
+if __name__ == '__main__':
+    main()