The Ping Command

Ping is very useful if you
wish to lookup an IP address
for a website. For example:

ping www.websiterepairguy.com

OK. I just did a ping on my
own website.

Here's one of the lines of output:

64 bytes from box458.bluehost.com
   (74.220.219.58): 
   icmp_seq=1 ttl=52 time=86.0 ms

Ping will keep pinging away and
produce many many lines of output
that looks like the above.

Here's how to limit ping to one
line of output only:

ping -c 1 www.websiterepairguy.com

OK. Now my website gets pinged once
and then ping quits. In most cases,
this is what I want. I only need to
ping once.

Here's the total output for pinging
my website just once:

PING websiterepairguy.com 
    (74.220.219.58) 56(84) 
    bytes of data.
    64 bytes from 
    box458.bluehost.com 
    (74.220.219.58): 
    icmp_seq=1 ttl=52 
    time=90.2 ms

--- websiterepairguy.com 
    ping statistics ---
    1 packets transmitted, 
    1 received, 
    0% packet loss, 
    time 0ms
    rtt min/avg/max/mdev = 
    90.219/90.219/90.219/0.000 ms

Now let's say I'm only interested in
one thing and that is the IP address
for my website.

In this case, I'm only interested in
one line of output, the line that reveals
my IP addresss.

If I pipe the ping command to the grep
command, it might look like this:

ping -c 1 www.websiterepairguy.com | 
     grep PING

OK. The grep command narrows the amount
of output I get to just one line and only one
line of output. Here's that one line:

PING websiterepairguy.com 
     (74.220.219.58) 56(84) bytes of data.

How does grep work? It is a line printer
but a very special line printer. It only prints
lines that match what you gave it.

Since I gave it a capital PING as a pattern
to match, it only prints lines that match this
pattern.

Now lets narrow the output further. Let's
go for my domain name and my IP address only.
Here's the command:

ping -c 1 www.websiterepairguy.com | 
     grep PING | cut -f2-3 -d " "

Note the addition of the cut command.
I'm cutting out fields two and three based
on the spacebar as my field delimator.

Delimators are what define fields. They are
field separator characters.

I've placed a spacebar character between double
quotes to indicate that is my delimator. Here's
what it looked like when I did this:

-d " "

I only want the second and third field. Here's
how I specified this:

-f2-3

Here's the whole command again:

ping -c 1 www.websiterepairguy.com | 
      grep PING | cut -f2-3 -d " "

Here's the output to this command:

websiterepairguy.com (74.220.219.58)

OK. The only undersireable that remains
is the parenthesis. Here's a tricky way
to get rid of these:

ping -c 1 www.websiterepairguy.com | 
     grep PING | cut -f2-3 -d " " | 
     sed s/[\(\)]//g

In this case, the syntax for the sed
command is not very pretty. Here's what the
sed looks like:

sed s/[\(\)]//g

The sed command is being asked to substitute
one thing for another. In this case, it is being
asked to substitute parenthesis for nothing.

More simply, take the parenthesis out, both left
and right, and replace them with nothing.

The parenthesis appear with a backslash in front
because without the backslash, the parenthesis take
on a special meaning.

The sed command is using its own substitution
operator. Here's how the sed command works:

sed s/before/after/g

before is replaced by after

Here's the whole command again:

ping -c 1 www.websiterepairguy.com | 
      grep PING | 
      cut -f2-3 -d " " | 
      sed s/[\(\)]//g

Here's the output:

websiterepairguy.com 74.220.219.58

Ok. Seems like a lot of code but
actually, it is a quick way to get
things done, once you know what you
are doing.

Ed Abbott