What's the Correct Way to Do a Read with While Loop

Question

I came to a section of a bash book that is trying to show me that you can use a read statement in conjunction with a while loop to read each line of a file, and then capture the first two words into two variables. However, I wrote my own script to test it below.

$ cat hoststest 
192.168.1.1 pc1 word3 word4
192.168.1.2 pc2 word3 word4
$ cat t13
#!/bin/bash
while read ip_address pc_number restofstuff
do
if [ ! -z "$ip_address" ]; then
    echo "IP is $ip_address and its for $pc_number"
fi
done < "/home/john/hoststest"
$ ./t13
IP is 192.168.1.1 and its for pc1
IP is 192.168.1.2 and its for pc2

In my original test I did not have the third variable "restofstuff". What happened was that instead of the pc_number variable getting just either pc1 or pc2 as it's value, pc_number was being stored as the rest of the line. So I added this third variable to just not get all the rest of the line as part of the pc_number. What I've done works now, with this "restofstuff" variable, but it doesn't feel like I'm doing this right. I've just basically made a "dead" variable that does nothing. If I was trying to carry on with using the read + while loop, what would be the right way to go about it (note, it's the while loop + read combination I'm working with/learning, so I want to stay focused on that).

Answer 1

That’s just how read works: if there are more fields in its input than variables, the last variable is assigned the corresponding field and all the left-overs. Typical practice is to name this variable _:

while read ip_address pc_number _

See Understanding "IFS= read -r line" for an in-depth discussion of read, and Why is using a shell loop to process text considered bad practice?