Shell Programming and Scripting

Dear community,
I've a continuos tcpdump on redhat that close the dumped file every 100000 captured packets.

To avoid disk full I would like to gzip the closed *.cap file. But how can I check if the file is currently opened by tcpdump and skip it from gzip?

Thanks!

EDIT: Just to post an example:
I have currently the following file on the trace directory:

Code:

-rwxr-xr-x 1 root root      249 Aug  9  2011 cont_tcpdump.sh
drwx------ 2 root root     4096 Dec 13  2011 lost+found
-rw-r--r-- 1 root root 16558574 Mar 16 18:37 tcpdump_continuous_20130316_183340.cap
-rw-r--r-- 1 root root 17322400 Mar 16 18:40 tcpdump_continuous_20130316_183708.cap
-rw-r--r-- 1 root root 15552512 Mar 16 18:44 tcpdump_continuous_20130316_184049.cap
-rw-r--r-- 1 root root  6029312 Mar 16 18:45 tcpdump_continuous_20130316_184437.cap

The last file (tcpdump_continuous_20130316_184437.cap) is currently opened by tcpdunp, so my other script should run every 5 minutes and gzip only the closed *.cap files!