A Bash script that can verify the validity of the given IP address string

#! /Bin/bash
Validate_ipaddress (){
Declare-I ipart1
Declare-I ipart2
Declare-I ipart3
Declare-I ipart4

Inputip = $1
# Validate it
If [-Z $ inputip]; then
Return 1
Fi

Echo $ inputip | grep-e-Q "[0-9] {1, 3 }\. [0-9] {1, 3 }\. [0-9] {1, 3 }\. [0-9] {1, 3 }"
If [$? -Ne 0]; then
Return 1
Fi

# Separate the IP address
Ippart1 =$ {inputip % .*}
Inputip =$ {inputip #*.}
Ippart2 =t2 {inputip % .*}
Inputip =$ {inputip #*.}
Ippart3 =t3 {inputip % .*}
Ippart4 =$ {inputip #*.}

# Check whether the IP number begins with zero, that is wrong syntax
# If the string begins with zero, bash cannot convert it into integer correctly
# Ipart1 and ipart4 cannot be zero
If echo $ ippart1 | grep-Q "^ 0" | echo $ ippart4 | grep-Q "^ 0"; then
Return 1
Fi

If [$ ippart2! = "0"] & Echo $ ippart2 | grep-Q "^ 0"; then
Return 1
Fi

If [$ ippart3! = "0"] & Echo $ ippart3 | grep-Q "^ 0"; then
Return 1
Fi

Ipart1 = ippart1
Ipart2 = ippart2
Ipart3 = ippart3
Ipart4 = ippart4
If [$ ipart1-GT 254] | [$ ipart2-GT 254] | [$ ipart3-GT 254] | [$ ipart4-GT 254]; then
Return 1
Fi

Return 0
}

If validate_ipaddress $1; then
Echo "legal"
Else
Echo "illegal"
Fi

Note that the {m, n} syntax is used in the RE to verify whether the IP address is valid. In this way, grep is written with-e option, because this is an extension syntax, in some UNIX and Linux grep, this syntax is also supported without-E (basic mode, non-extended mode), but it must be written as a style like \ {M, N \}.