Command timeout from inside script. Post: 302594892

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Top Forums Shell Programming and Scripting Command timeout from inside script. Post 302594892 by gencon on Wednesday 1st of February 2012 11:58:22 AM

02-01-2012

Registered User

Command timeout from inside script.

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.

gencon

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curlopt_timeout

CURLOPT_TIMEOUT(3)					     curl_easy_setopt options						CURLOPT_TIMEOUT(3)

NAME

       CURLOPT_TIMEOUT - set maximum time the request is allowed to take

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TIMEOUT, long timeout);

DESCRIPTION

       Pass  a long as parameter containing timeout - the maximum time in seconds that you allow the libcurl transfer operation to take. Normally,
       name lookups can take a considerable time and limiting operations to less than a few minutes risk  aborting  perfectly  normal  operations.
       This option may cause libcurl to use the SIGALRM signal to timeout system calls.

       In unix-like systems, this might cause signals to be used unless CURLOPT_NOSIGNAL(3) is set.

       If both CURLOPT_TIMEOUT(3) and CURLOPT_TIMEOUT_MS(3) are set, the value set last will be used.

       Since  this puts a hard limit for how long time a request is allowed to take, it has limited use in dynamic use cases with varying transfer
       times. You are then advised to explore CURLOPT_LOW_SPEED_LIMIT(3), CURLOPT_LOW_SPEED_TIME(3) or using CURLOPT_PROGRESSFUNCTION(3) to imple-
       ment your own timeout logic.

DEFAULT

       Default timeout is 0 (zero) which means it never times out during transfer.

PROTOCOLS

       All

EXAMPLE

       CURL *curl = curl_easy_init();
       if(curl) {
	 curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");

	 /* complete within 20 seconds */
	 curl_easy_setopt(curl, CURLOPT_TIMEOUT, 20L);

	 curl_easy_perform(curl);
       }

AVAILABILITY

       Always

RETURN VALUE

       Returns CURLE_OK

SEE ALSO

       CURLOPT_TIMEOUT_MS(3), CURLOPT_CONNECTTIMEOUT(3), CURLOPT_LOW_SPEED_LIMIT(3),

libcurl 7.54.0							 February 03, 2016						CURLOPT_TIMEOUT(3)