internet connection tester script

[kellyremo]

http://pastebin.com/raw.php?i=rykHdvBh

bix.hu and www.yahoo.com are "pingable" test sites.
127.0.0.1 could not be pinged [firewall drops all icmp]

i have a "oneliner" that echoes if theres "internet connection or
no".
$ ping -W 1 -c 2 bix.hu >& /dev/null && ping -W 1 -c 2
www.yahoo.com >& /dev/null && echo "internet
connection ok" || echo "no internet connection"
internet connection ok
$ ping -W 1 -c 2 127.0.0.1 >& /dev/null && ping -W 1 -c 2
www.yahoo.com >& /dev/null && echo "internet
connection ok" || echo "no internet connection"
no internet connection
$ ping -W 1 -c 2 127.0.0.1 >& /dev/null && ping -W 1 -c 2
127.0.0.1 >& /dev/null && echo "internet connection
ok" || echo "no internet connection"
no internet connection
$ ping -W 1 -c 2 bix.hu >& /dev/null && ping -W 1 -c 2
127.0.0.1 >& /dev/null && echo "internet connection
ok" || echo "no internet connection"
no internet connection
$ ping -W 1 -c 2 bix.hu >& /dev/null && ping -W 1 -c 2
www.yahoo.com >& /dev/null && echo "internet
connection ok" || echo "no internet connection"
internet connection ok
$

Ok!

But: if i want the "oneliner" to only go along when theres internet connection:
$ while $TORF; do ping -W 1 -c 1 bix.hu >& /dev/null &&
ping -W 1 -c 1 www.yahoo.com >& /dev/null && TORF=false ||
TORF=true; done
$ while $TORF; do ping -W 1 -c 1 127.0.0.1 >& /dev/null &&
ping -W 1 -c 1 www.yahoo.com >& /dev/null && TORF=false ||
TORF=true; done
$ while $TORF; do ping -W 1 -c 1 127.0.0.1 >& /dev/null &&
ping -W 1 -c 1 127.0.0.1 >& /dev/null && TORF=false ||
TORF=true; done
$ while $TORF; do ping -W 1 -c 1 bix.hu >& /dev/null &&
ping -W 1 -c 1 127.0.0.1 >& /dev/null && TORF=false ||
TORF=true; done
$ while $TORF; do ping -W 1 -c 1 bix.hu >& /dev/null &&
ping -W 1 -c 1 www.yahoo.com >& /dev/null && TORF=false ||
TORF=true; done
$ 

It just doesn't work. 

Goal: if theres no internet connection, then the oneliner must loop until there is
internet connection. if theres internet connection the oneliner ends.

what am i missing?

[Bryn M. Reeves]

On 01/28/2011 11:28 AM, kellyremo wrote:
>  
>  http://pastebin.com/raw.php?i=rykHdvBh
>  
>  bix.hu and www.yahoo.com are "pingable" test sites.
>  127.0.0.1 could not be pinged [firewall drops all icmp]
>  
>  i have a "oneliner" that echoes if theres "internet connection or
> no".
>  $ ping -W 1 -c 2 bix.hu >& /dev/null && ping -W 1 -c 2 www.yahoo.com
> >& 
>  /dev/null && echo "internet connection ok" || echo "no internet
> connection"
>  internet connection ok
>  $ ping -W 1 -c 2 127.0.0.1 >& /dev/null && ping -W 1 -c 2 www.yahoo.com
> >& 
>  /dev/null && echo "internet connection ok" || echo "no internet
> connection"
>  no internet connection
>  $ ping -W 1 -c 2 127.0.0.1 >& /dev/null && ping -W 1 -c 2 127.0.0.1
> >& /dev/null 
>  && echo "internet connection ok" || echo "no internet
> connection"
>  no internet connection
>  $ ping -W 1 -c 2 bix.hu >& /dev/null && ping -W 1 -c 2 127.0.0.1 >&
> /dev/null && 
>  echo "internet connection ok" || echo "no internet connection"
>  no internet connection
>  $ ping -W 1 -c 2 bix.hu >& /dev/null && ping -W 1 -c 2 www.yahoo.com
> >& 
>  /dev/null && echo "internet connection ok" || echo "no internet
> connection"
>  internet connection ok
>  $
>  
>  Ok!
>  
>  But: if i want the "oneliner" to only go along when theres internet
> connection:
>  $ while $TORF; do ping -W 1 -c 1 bix.hu >& /dev/null && ping -W 1 -c 1 
>  www.yahoo.com >& /dev/null && TORF=false || TORF=true; done
>  $ while $TORF; do ping -W 1 -c 1 127.0.0.1 >& /dev/null && ping -W 1 -c 1
>
>  www.yahoo.com >& /dev/null && TORF=false || TORF=true; done
>  $ while $TORF; do ping -W 1 -c 1 127.0.0.1 >& /dev/null && ping -W 1 -c 1
>
>  127.0.0.1 >& /dev/null && TORF=false || TORF=true; done
>  $ while $TORF; do ping -W 1 -c 1 bix.hu >& /dev/null && ping -W 1 -c 1
> 127.0.0.1 
>   >& /dev/null && TORF=false || TORF=true; done
>  $ while $TORF; do ping -W 1 -c 1 bix.hu >& /dev/null && ping -W 1 -c 1 
>  www.yahoo.com >& /dev/null && TORF=false || TORF=true; done
>  $
>  
>  It just doesn't work.
>  
>  Goal: if theres no internet connection, then the oneliner must loop until there 
>  is internet connection. if theres internet connection the oneliner ends.
>  
>  what am i missing?
>   
Instead of using a variable (that has funky scoping in shell) just make the &&
compound command the loop condition and place it in a subshell:

while (! ping -W 1 -c 1 bix.hu && ! ping -W 1 -c 1 www.yahoo.com
)&>/dev/null;
do /bin/true ; done

Or you can write the same as:

while (! (ping -W 1 -c 1 bix.hu && ping -W 1 -c 1
www.yahoo.com))&>/dev/null; do
/bin/true ; done

It's probably not the best way to do it though - this little shell loop eats up
fair bit of CPU time.

Just putting a "sleep 1" instead of /bin/true makes the load barely noticable
but if you're on a system that's using Network Manager then you could also look
at the information provided by the nmcli tool to see if it would meet your
requirements.

Regards,
Bryn.

[JB]

kellyremo <kellyremo <at> zoho.com> writes:

>  ... 
>  Goal: if theres no internet connection, then the oneliner must loop until
>  there is internet connection. if theres internet connection the oneliner
>  ends.what am i missing?
>  ... 
Test:

1. there is internet connection to both

$ TORF=true; while $TORF; do ping -W 1 -c 1 bix.hu >& /dev/null && ping -W
1
-c 1 www.yahoo.com >& /dev/null && TORF=false || TORF=true; echo $TORF;
sleep 1;
done
false
$

2. there is no internet connection to at least one

$ TORF=true; while $TORF; do ping -W 1 -c 1 www.blakstar.org >& /dev/null
&&
ping -W 1 -c 1 www.yahoo.com >& /dev/null && TORF=false || TORF=true; echo
$TORF; sleep 1; done
true
true
true
true
^C
$

Nota bene !
Let's assume negation is represented by "~" sign.
~(a && b) equivalent to ~a || ~b
~(a || b) equivalent to ~a && ~b

JB