Wait for file existence

[CJason]

Inside my perl script, I need to wait for the existence of a file before continuing. Is there a good way to do this?

Thanks in advance!

 

[133tcamel]

if it's not production level code, you can do away with this:

sleep 1 while ( !(-e "c:/tmp.txx") );

---
cheers!
san

print length "The answer to life, universe & everything!

 

[CJason]

What does this statement do exactly:

sleep 1 while ( !(-e "c:/tmp.txx") );

I know what the "while ( !(-e "c:/tmp.txx") );" does, but what exactly does the "sleep 1" do? Is it basically:

If the file does not exist, wait a second then check again?

Thanks!!

 

[Kirsle]

Yep.

 

[133tcamel]

yes, that is correct. which is why i would suggest not using it for a production server.

The reason for using sleep inside the while loop is because sleep suspends the process and hence there is no noticable CPU utilization until the next check.

---
cheers!
san

print length "The answer to life, universe & everything!

 

[CJason]

133tcamel, do you know if using syscall...with a call to something like WAIT...suspends the process? I would like to "sleep" for less than 1 second, but I don't think I can do that with the sleep command.

Thanks again!!!

 

[133tcamel]

if you'd like to sleep for less than a second, try using Time::HiRes. It allows you to sleep in microseconds.

There is also something about file triggers (linux), i once browsed in a book which could be a TIMTOWTDI. But I wouldn't go that route unless really neccessary.

---
cheers!
san

print length "The answer to life, universe & everything!

 

[Kirsle]

Something else you can try:

while (1) {
   last if -e "C:/tmp.txt";
}

I'm not sure what effect this has on CPU usage, but it doesn't use sleeps, it just breaks free of the loop as soon as the file exists.

 

[CJason]

Kirsle, Yes, that takes up CPU...I KNOW because that is similar to what I originally tried, and I took down the system!?!?!?