On Fri, Oct 4, 2013 at 2:20 PM, Kunszt Árpád < arpad.kun...@syrius-software.hu> wrote:
> I tried to use "read -t 0" to check if there is any data on the STDIN or > not. > > The man page said: > > If timeout is 0, read returns success if input is available on the > specified file descriptor, failure otherwise. > > Maybe I made a mistake but I tested and I got variable results: > > arpad@terminus ~ $ for(( i=0; i<10; i++ )); do echo -n "a" | read -t 0 ; > echo $?; done | sort | uniq -c > 10 0 > arpad@terminus ~ $ for(( i=0; i<10; i++ )); do echo -n "a" | read -t 0 ; > echo $?; done | sort | uniq -c > 8 0 > 2 1 > arpad@terminus ~ $ for(( i=0; i<10; i++ )); do echo -n "a" | read -t 0 ; > echo $?; done | sort | uniq -c > 10 0 > > I tried this on 2 machines with the same results: > > GNU bash, version 4.1.5(1)-release (x86_64-pc-linux-gnu) > GNU bash, 4.2.45(1)-release (x86_64-pc-linux-gnu) verzió > > > Am I doing something wrong? Did I misunderstand the documentation? Or is > there a race condition? > > Thanks, > > Arpad Kunszt There is a race condition, you cannot know if echo will run before read.
