[Tutor] tail -f

[Danny Yoo]

> So basically, they open the file, and just stare at it's size, forever (or
> until the user gets tired).  Whenever the file size changes, it just
> prints the remainder out to screen.  They do something like a time.sleep()
> to make the busy waiting look less bad.  *grin* By default, they poll
> every 1 second:
>
> /***/
> static unsigned int sleep_interval = 1;
> /***/


Here's an example of how we might do it in Python:


###
#!/usr/local/bin/python

"""A demonstration of file following.

Danny Yoo (dyoo@hkn.eecs.berkeley.edu)

"""

import os.path, time, sys

DELAY=1

def follow(filename):
    f = open(filename)
    size = 0
    while 1:
        new_size = os.path.getsize(filename)
        if new_size > size:
            f.seek(size)
            sys.stdout.write(f.read())
        elif new_size < size:
            print "=== File truncation ==="
        size = new_size
        time.sleep(DELAY)


if __name__ == '__main__':
    if len(sys.argv) != 2:
        print "We need a file!"
    else:
        follow(sys.argv[1])
###



Hope this helps!