Shell counts all strings before the last occurrence of a string

demand ：

I want to count some ip Network segment .

Example ：

There's a server ip yes 192.168.144.249, I want to count 192.168.144 This segment .

Method 1 ：

strToCheck='192.168.144.251'

letpos=`echo "$strToCheck" | cut -d '.' -f 1,2,3`

echo $letpos

The result is 192.168.144

Method 2 is more complicated ：

# Count the last one first . In which position

strToCheck='192.168.144.249'
charToSearch='.'
letpos=`echo "$strToCheck" | awk -F ''$charToSearch'' '{printf "%d", length($0)-length($NF)}'`

# Then count the string in front of the position

echo ${strToCheck:0:$letpos}

result 192.168.144.

-- This article is from ：Shell Script implementation finds the last position of a character in the string / Sheng Rong Zhang