How read line by line in bash and assign the value to a variable

Question

I have a file called ips.txt and it has values like below:

cat ips.txt

abc.com.   10.120.20.4 10.120.20.5 ... # there can be many ips separated by a space
xyz.com.   10.120.20.6

I want to read this file line by line with a loop and do some other works.

And als I need to remove that . as well at the end of each domain name abc.com. and assign each ip to a variable (if it can be stored to an array, it is great)

So here's what I tried:

input="ips.txt"
while IFS= read -r line
do
  echo "$line"
  domain="" # need to assign abc.com
  ip_one= "" # need to assign the first ip occurence
  ip_two= "" # need to assign the second ip occurence
  ...
  ip_n= "" # need to assign the nth ip occurence

  # some other commands I need to execute with domain name and all the ips collected
done < "$input"

how can I assign the ip values to different variables? and use them? It is better if I can Store the IP's in a array like data type so it is more easier as I don't know how many IP's are there for some line in the ips.txt file.

Can someone help me do this?

If you can specify what you want to do with the ips you may get much better answers/advice. Arrays or variables should be the last resort. — perreal, Oct 27 '20 at 17:27
`need to remove that . as well at the end of each domain name abc.com. ` → a domain name ends with a dot, this is the norm. If your implementation software does not support the end dot, then it is broken See: https://stackoverflow.com/questions/19480767 — Léa Gris, Oct 27 '20 at 18:07

Paul Hodges · Answer 1 · 2020-10-27T18:17:37.350

0

Start with a standard array read. Assign to $@, use parameter expansion to strip the dot, then shift it off the stack, and you can assign back to your original array.

input="ips.txt"
declare -A lookup=()
while read -a ips # ips is an array
do set -- "${ips[@]}"  # assign the array to $@
   domain="${1%.}"     # assign abc.com without the dot
   shift               # dump the first column; now $@ is just the IP's
   for ip in "$@"; do lookup[$ip]="$domain"; done # assign the domain to each IP
done < "$input"

now

$: echo ${lookup[10.120.20.5]}
abc.com

edited Oct 27 '20 at 18:17

answered Oct 27 '20 at 17:23

Paul Hodges

13,382
1
17
36

the `IFS=` looks strange, shouldn't it be `IFS=' '`? `set -- "${ips[@]}"` you may `unset ips[0]` in a similar fashion to `shift`. Or `ips=("${ips[@]:1}")` – KamilCuk Oct 27 '20 at 17:31
when I try to `echo $ips` it doesn't print any values. prints empty output – Jananath Jayarathna Oct 27 '20 at 17:49
And ` domain="${1%.}"` still prints domains with `.` at the end... i think this code is not properly working. – Jananath Jayarathna Oct 27 '20 at 17:51
I think I was briefly considering adding `.` to IFS but that would have broken a lot of things, and somehow it got left there. Apologies to all. – Paul Hodges Oct 27 '20 at 17:59
Would have been more educative to inform poster he is duplicating a question and flag the question as dupe. – Léa Gris Oct 27 '20 at 18:04
@PaulHodges now it works, but let's say we need to ping the each ip belongs to each domain how can I do that? I thought there should be another loop to do that. How can I do this with your answer – Jananath Jayarathna Oct 27 '20 at 18:07

perreal · Accepted Answer · 2020-10-27T18:19:20.517

0

Using set, and shift:

while IFS= read -r line; do       
  set $line                       
  domain=$(sed 's/\.$//' <<< "$1")                     
  shift                           
  for ip in $@; do                                    
    echo "domain: $domain ip: $ip"
  done                            
done < "$input"

edited Oct 27 '20 at 18:19

answered Oct 27 '20 at 18:06

perreal

94,503
21
155
181

How can I remove the `.` at the end of the domain? – Jananath Jayarathna Oct 27 '20 at 18:17
you can use sed, updated with an example. – perreal Oct 27 '20 at 18:19

How read line by line in bash and assign the value to a variable

2 Answers2