Isolate the last octet from an IP address and put it in a variable

Question

The following script:

IP=`ifconfig en0 inet | grep inet | sed 's/.*inet *//; s/ .*//'`

isolates the IP address from ipconfig command and puts it into the variable $IP. How can I now isolate the last octet from the said IP address and put it in a second variable - $CN

for instance:

$IP = 129.66.128.72 $CN = 72 or $IP = 129.66.128.133 $CN = 133...

Solution 1

Shortcut:

read IP CN < <(exec ifconfig en0 | awk '/inet / { t = $2; sub(/.*[.]/, "", t); print $2, t }')

Solution 2

Use "cut" command with . delimiter:

IP=129.66.128.72
CN=`echo $IP | cut -d . -f 4`

CN now contains the last octet.

Solution 3

In BASH you can use:

ip='129.66.128.72'
cn="${ip##*.}"
echo $cn
72

Or using sed for non BASH:

cn=`echo "$ip" | sed 's/^.*\.\([^.]*\)$/\1/'`
echo $cn
72

Using awk

cn=`echo "$ip" | awk -F '\\.' '{print $NF}'`

Solution 4

I would not use ifconfig to get the IP, rather use this solution, since it gets the IP needed to get to internet regardless of interface.

IP=$(ip route get 8.8.8.8 | awk '{print $NF;exit}')

and to get last octet:

last=$(awk -F. '{print $NF}' <<< $IP)

or get the last octet directly:

last=$(ip route get 8.8.8.8 | awk -F. '{print $NF;exit}')

View more solutions

Comments

[Jotne]

You can shorten it some to:CN=$(cut -d. -f4 <<<$IP)

[Admin]

Shorter using awk cn=$(awk -F. '$0=$4' <<< $ip)

[anubhava]

@Jidder: I believe only BASH supports <<< that's why I used pipes in non BASH solutions.

[Admin]

Oh okay,didn't know it was specific to bash, is $() bash specific as well ?

[chepner]

No, $(...) is in the POSIX standard.

[chepner]

<<< is non-standard and not supported by all shells.

[chepner]

<( ... ) is non-standard and not supported by all shells.

[anubhava]

Ah that is correct, thank for correcting @chepner me. Always helpful.