CODEWITHSUNDEEP
sed
bobby
bobby

Reputation: 189

How to interchange the fqdn <-> hostname in hosts file

I am trying to update the format in /etc/hosts file. sample

# more /etc/hosts

14.5.10.13 host1 host1.mydomain.com
14.5.10.14 host2 host2.mydomain.com
#

to 

14.5.10.13 host1.mydomain.com host1
14.5.10.14 host2.mydomain.com host2

I tried this but didnt worked. Please suggest.

#sed 's/host{1,2} /host{1,2}.mydomain.com/' /etc/hosts

Upvotes: 1

Views: 155

Answers (1)

John1024
John1024

Reputation: 113814

To swap the second and third fields in the file hosts but only if the second is host1 or host2:

$ awk '$2~/^host[12]$/{a=$2; $2=$3; $3=a} 1' hosts
# more /etc/hosts

14.5.10.13 host1.mydomain.com host1
14.5.10.14 host2.mydomain.com host2
#

Here, $2~/^host[12]$/ selects only those lines whose second field matches one of the hosts of interest. For those lines, the second and third field are swapped. The final 1 is awk's cryptic shorthand for print-the-line.

To do something similar with sed:

$ sed -E '/ host[12] /{s/ (host[12]) ([[:alnum:].]*)/ \2 \1/}' hosts
# more /etc/hosts

14.5.10.13 host1.mydomain.com host1
14.5.10.14 host2.mydomain.com host2
#

Here, / host[12] / selects only those lines that contain host1 or host2 surrounded by spaces. For those lines, host1 or host2 is swapped with the word that follows.

Upvotes: 1

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