April 23, 2007

Real Tail'ing in Python

or, finding last few lines in a file.

Ok. So, last solution was not perfect. It just returned last line from a file. What about returning say 10 or may be more lines? Here is the modified Tail function to do that:
def Tail(filepath, nol=10, read_size=1024):
This function returns the last line of a file.
filepath: path to file
nol: number of lines to print
read_size: data is read in chunks of this size (optional, default=1024)
IOError if file cannot be processed.
f = open(filepath, 'rU') # U is to open it with Universal newline support
offset = read_size
f.seek(0, 2)
file_size = f.tell()
while 1:
if file_size < offset:
offset = file_size
f.seek(-1*offset, 2)
read_str = f.read(offset)
# Remove newline at the end
if read_str[offset - 1] == '\n':
read_str = read_str[:-1]
lines = read_str.split('\n')
if len(lines) >= nol: # Got nol lines
return "\n".join(lines[-nol:])
if offset == file_size: # Reached the beginning
return read_str
offset += read_size

You can call it in your program like this:
Tail('/var/log/syslog') or,
Tail('/etc/httpd/logs/access.log', 100)
Useful, Isn't it?


1 comment:

  1. Hi Manu

    You changed your profile, I didnt observe that, when you have done that. Now you are in Hyderabad !!!! so Howz the SOUTH?