CODEWITHSUNDEEP
bashparsingawkmatchmatching
WesZ
WesZ

Reputation: 139

awk matching incorrect hostname in /etc/hosts

I am using this awk code to pick out an IP address in the /etc/hosts file and although I can force it to match the correct hostname, awk will select an "almost like" hostname if it see's it first. I have researched this and I cannot figure it out.

sUSER=machine_005
ip=$(awk '/^[[:space:]]*($|#)/{next}/'$sUSER'/{print $1; exit}' /etc/hosts)

I know the first part looks for $ or # and if found calls the next line. This feature is needed in the final formula. The other feature needed is to stop after the first match. I know that the next /xxx/ searches for the pattern and if found prints $1 to $ip.

Here is a sample of my hosts file

555.555.555.555 machine.005
222.222.222.222 machine_005

if I $sUSER=machine_005 $ip is 222.222.222.222 just like you'd expect.

if I $sUSER=machine.005 $ip is 555.555.555.555 just like you'd expect

But if my /etc/hosts is:

222.222.222.222 machine_005
555.555.555.555 machine.005

Then if I $sUSER=machine_005 $ip is 222.222.222.222 just like you'd expect.

However, if I $sUSER=machine.005 $ip is 222.222.222.222 It takes machine_005 ip address.

Could this be a bug? or is this on purpose?

Thanks.

Hello. I wanted to post my final line of code that provides the correct output. I appreciate all of the help and guidance from those who responded. I wanted to post the final code in case someone in the future can find it useful.

 ip=$(awk -v sUSER=$sUSER 'BEGIN{gsub(/\./,"\\.",sUSER)}match($0,/[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+/) && $0 ~ ("[^[:alpha:]]"sUSER"$") && $0 !~ /^$/ && $0 !~ /^#/{print $1}' /etc/hosts)

Upvotes: 0

Views: 616

Answers (2)

hek2mgl
hek2mgl

Reputation: 158260

getent is a tool meant to retrieve entries from /etc/hosts (and other config databases):

getent hosts "${USER}" | cut -d' ' -f1

Upvotes: 1

Barmar
Barmar

Reputation: 782693

In a regular expression, . matches any character. You need to escape it to make it match literally.

sUser='machine\.005'

If you're getting the value from user input, you can use the shell's substitution operator:

sUser=${sUser//./\\.}

Also see How do I use shell variables in an awk script? for a better way to incorporate the shell variable into the awk script.

Upvotes: 1

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