boyeestudio wrote:
> The following program have the same function as the linux's command:tail
> -f logfile.log
> But it print a lot of blank lines while showing on the stdout.
> How to fix this problem and let it go ahead always
> showing the end line as the log file's increasing.
>
> #tail.py:
>
> import os
> import sys
>
> class Tail:
> def __init__(self,inputstream):
> self.inputstream=inputstream
>
> def tail(self):
> self.inputstream.seek(0,2) ???Maybe this is where I'll need
> fixed,But I don't know how to....
You probably want to move to the end of the file once at the
beginning of the script, not before every attempt to read from it...
> line=self.inputstream.readline().strip()
Don't strip() so fast. You lose the information whether you have reached the
(current) end of file or a blank line (readline() returns "" or "\n"
respectively).
> print line
>
> if __name__=="__main__":
> if len(sys.argv)<=1:
> print "You must type a log file name"
> sys.exit()
> arg=file(sys.argv[1],'r+')
> while(arg):
That's always true, I think.
> try:
> t=Tail(arg)
> t.tail()
> except KeyboardInterrupt:
> arg.close()
> print "File closed"
A no-fluff version might be
filename = sys.argv[1]
infile = open(filename, "r")
infile.seek(0, 2)
while True:
while True:
line = infile.readline()
if not line: # an empty string indicates eof
break
print line,
time.sleep(1) # give the writing program a chance to write more lines
The inner loop can also be written
for line in iter(infile.readline, ""):
print line,
Peter
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