Shell Programming and Scripting

Hello Experts,

I need to write a shell script to check if a file is open and something is being written to it. I want to know how OS handles it. I checked with lsof command but it is not working. For a test I did this.

then I checked

lsof | grep -i /home/admin/abc.txt

It did not show any open process to me.

Yesterday when I tried the same thing, it once showed up i.e. I could see the output of lsof command but then again it disappeared.

I also tried the same by opening a file through vi but no luck.


I also want to know how system behaves for a file that is being open through vi, gedit etc and the one that is being appended through a loop or some script.

How about fuser

Thanks for the advise. Can you please duplicate my testing script and show me how fuser handles this?

Your loop constantly closes and opens the output file for append, so whether you see something with lsof becomes a race condition.

Instead try:

Code:

while true; do echo `date` ; done >abc.txt

or to append:

Code:

while true; do echo `date` ; done >>abc.txt

In both cases the output file is opened once and kept open the whole time for the duration of the loop.

Thank you so much. That's what I was looking for. Now I will check in my script how I can I implement this.

How about:

Code:

lsof abc.txt

Or, what you probably initialy (wanted to) tried:

Code:

lsof | grep -i abc.txt

Or even:

Code:

USERNAME=$USER
lsof /path/to/abc.txt | grep $USERNAME

To check if the file is open by a specific person.

hth