Adding elements in a Bash array to print them later

Question

I am adding elements on an array (Add a new element to an array without specifying the index in Bash) but I am getting an unexpected result. I suppose I am doing something wrong when adding elements in the array and/or when iterating the array to print its values.

Code:

for name in $(cat list.txt); do
    host $name.$DOMAIN | grep "has address" | cut -d" " -f4
done

for name in $(cat list.txt); do
    echo "."
    IPS+=(`host $name.$DOMAIN | grep "has address" | cut -d" " -f4`)
    echo ${#IPS[@]}
done

for ip in $IPS; do
    echo "IP: $ip"
done

Output:

12.210.145.45
67.20.71.219
75.58.197.10
31.70.88.22
.
1
.
3
.
4
.
4
.
4
IP: 12.210.145.45

Expected output:

Output:

12.210.145.45
67.20.71.219
75.58.197.10
31.70.88.22
.
1
.
2
.
3
.
4
IP: 12.210.145.45
IP: 67.20.71.219
IP: 75.58.197.10
IP: 31.70.88.22

See DontReadLinesWithFor re: the for ip in $(cat ...) idiom, and also the related BashPitfalls #1. — Charles Duffy
– Charles Duffy, Commented Aug 3, 2018 at 17:21
Similarly, addr=$(host "$name.$DOMAIN" | grep "has address" | cut -d" " -f4)"; if [[ $addr ]]; then ips+=( "$addr" ); fi would be more reliable. (Does assume you fix your variable case, but that's a thing you should do). — Charles Duffy
– Charles Duffy, Commented Aug 3, 2018 at 17:22
That said, replacing host with dig +short would make this whole thing a lot simpler; do that and you don't need to mess with grep or cut at all. — Charles Duffy
– Charles Duffy, Commented Aug 3, 2018 at 17:23

choroba · Accepted Answer · 2018-08-03 17:10:39Z

1

To iterate over an array, use

for ip in "${IPS[@]}" ; do

See PARAMETERS in man bash.

answered Aug 3, 2018 at 17:10

choroba

245k27 gold badges221 silver badges304 bronze badges

Sign up to request clarification or add additional context in comments.

12 Comments

user1156544 Over a year ago

Great thanks. Is there a reason why the logged "." is appearing more than 4 times? including the logged size as: 1, 3, 4, 4 instead of the expected 1,2,3,4.

choroba Over a year ago

maybe host $name.$DOMAIN | grep "has address" | cut -d" " -f4 returns more than one word?

Jason Over a year ago

This line must be failing to add to the list: IPS+=(`host $name.$DOMAIN | grep "has address" | cut -d" " -f4`). If list.txt has 4 lines of input and one of the lines has a space in it, you are going to loop 5 times. Try adding echo "$name" into one of the loops to see. Also, you can check out any error messages by adding 2>> error.txt to the end of host $name.$DOMAIN | grep "has address" | cut -d" " -f4 Error messages will display in error.txt

Charles Duffy Over a year ago

@Jason, ...the lack of quotes when you add an item means you aren't guaranteed that only (and at most) one will be added per iteration.

choroba Over a year ago

@Jason: No, that would concatenate a string, not add a new element to an array.

|

Collectives™ on Stack Overflow

Adding elements in a Bash array to print them later

1 Answer 1

12 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

12 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related