Hi,

I've written a very robust script to get an external IP address from 'behind' a router. It uses many web pages randomly choosing which one/ones to use at run time. The "fetch the web page containing the IP address" is handled by either wget or curl both of which have their 'max time for the operation' option set to 1 second. Most of the web servers respond within a max of 500ms, so the idea of having the timeout set to 1 second is so that if a server is slow to respond the script just moves on to another server.

I've noticed that neither curl nor wget actually keep to the timeout. On my machine this was not a problem, the timeout always kicked in at the latest of about 2.5 seconds. Over the last 24 hours I've tested the script on a Debian machine, having the script run 10 times every 5 mins. Looking at the results I've discovered that on 14 occasions (of the 7560) the timeout failed catastrophically, ranging from 27.722 to 170.643 seconds - the latter is almost 3 mins from a 1 sec timeout.

It seems that I'll have to write my own timeout routine. There are quite a lot of examples out there but the all seem to rely on either using the program 'timeout' (which is not POSIX), or using a timeout script, Eg. timeout_script -t 1 command - which is not what I need at all.

Here's a little bit of my code:

Code:

# curl command line for curl users.
curlCommand="curl --silent --max-time $timeout"

# wget command line for wget users.
wgetCommand="wget --quiet --timeout=$timeout --tries=1 --output-document=-"

urlDownloaderProg=$curlCommand

grepExpr="[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+"

ipAdd=$($urlDownloaderProg "$url" | grep -Eo "$grepExpr" | uniq)

What I need to do is for the line beginning 'ipAdd=' to return immediately, and then for the script to monitor its child process and kill it if it is not finished after 1 second. But I'm not sure how to do this - in particular how do I get the ipAdd= line to return immediately, I had problems using '&' both inside and outside the final ')', while still storing the results of the line in the variable ipAdd. Maybe I am going about this the wrong way and need a different approach.

Any help or advise would be greatly appreciated. Many thanks.