That's wrong. It suffers from a race condition. 

+===============================+===============================+
| Process 1                     | Process 2                     |
+===============================+===============================+
| open the status file          |                               |  T
| read the status (status is 1) |                               |  i
+-------------------------------+-------------------------------+  m
|                               | open the status file          |  e
|                               | read the status (status is 1) |  |
|                               | write 2 to the status file    |  |
|                               | proceed                       |  |
+-------------------------------+-------------------------------+  v
| write 2 to the status file    |                               |
| proceed                       |                               |
+===============================+===============================+

[download]

If you use flock, then it's just an extention of what the OP posted.

( Oops! Seems like tye posted something similar when I was writing this node. )

In reply to Re^2: Ensuring only one copy of a perl script is running at a time by ikegami
in thread Ensuring only one copy of a perl script is running at a time by eyepopslikeamosquito

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