From: "Wolfgang Nádasi-Donner" <wonado@...>
Date: 2007-01-26T04:10:10+09:00
Subject: Re: Regexp and string halts ruby

Ricardo Ramalho schrieb:
> I've tried the following regexp/string match:
> 
> /^((?:\s*.+[;=][^,]*,?)+)$/ =~ " pid=934, time=478611,
> command=TMQFORWARD, args=-C dom=ccaApp -g 650 -i 4278 -u pthp68 -U
> /home1/eclprp/logs/tx/ULOG -m 0 -- -i 10 -t 600 -q AW02,AW02S TMQFORWARD
> -C dom=ccaApp -g 650 -i 4278 -u pthp68 -U /home1/eclprp/logs/tx/ULOG -m
> 0 -- -i 10 -t 600 -q AW02, "
> 
> On a Debian/Linux system, with ruby version 1.8.4(-7sarge5) and even on
> the more recent 1.8.5(-4) ruby enters an infinite active loop, and never
> returns.
> 
> Can anyone confirm/deny this possible bug on different architectures?
> Thanks.
> 

There is no infinite loop - it it takes a long time, because your regular 
expression is possibly too complex. These "(...*...+...*...)+" constructs are 
dangerous. See "Mastering Regular Expressions - Friedl" for details.

An example with your regular expression and your string, starting with a short 
part an taken longer ones each step. The whole string may take some hundred 
years on my small machine ;-)

 >>>>> Code >>>>>

regex = /^((?:\s*.+[;=][^,]*,?)+)$/

string = " pid=934, time=478611,command=TMQFORWARD, args=-C dom=ccaApp -g 650 -i 
4278 -u pthp68, "
t = Time.new
string.match(regex)
puts "Match need appr. #{Time.now-t} seconds"
STDOUT.flush

string = " pid=934, time=478611,command=TMQFORWARD, args=-C dom=ccaApp -g 650 -i 
4278 -u pthp68 -U /home1/eclprp/logs/tx/ULOG, "
t = Time.new
string.match(regex)
puts "Match need appr. #{Time.now-t} seconds"
STDOUT.flush

string = " pid=934, time=478611,command=TMQFORWARD, args=-C dom=ccaApp -g 650 -i 
4278 -u pthp68 -U /home1/eclprp/logs/tx/ULOG -m 0 -- -i 10 -t 600 -q AW02,AW02S 
TMQFORWARD, "
t = Time.new
string.match(regex)
puts "Match need appr. #{Time.now-t} seconds"

 >>>>> Output >>>>>

Match need appr. 7.0 seconds
Match need appr. 21.38 seconds
Match need appr. 60.658 seconds

 >>>>> EoE >>>>>

Wolfgang Nádasi-Donner