Shell script determines whether IP is legitimate

Operations, shell scripts often encounter the legitimacy of determining the value entered, such as IP, email address, and so on. Then, according to their own script to summarize the judgment of IP legitimacy script to share to the netizen, when encountered can be a reference.

Idea: IP consists of four-bit numbers, divided by points, each field cannot be greater than 255, must conform to this format

Method 1:

Function check_ip ()  {    ip=$1    valid_check=$ (echo $ ip|awk -f.  ' $1<=255&&$2<=255&&$3<=255&&$4<=255{print  "Yes"} ')     if echo  $IP |grep -e  "^[0-9]{1,3}\. [0-9] {1,3}\. [0-9] {1,3}\. [0-9] {1,3}$ ">/dev/null; then        if [  $VALID _check  ==  "Yes"  ]; then             echo  "$IP  available."         else             echo  "$IP  not available!"         fi    else         echo  "$IP  not available!"     fi}# examplecheck_ip 192.168.1.1check_ip 256.1.1.1

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Method 2:

FUNCTION CHECK_IP ()  {    IP=$1    if [[  $IP  = ~ ^[0-9]{1,3}\. [0-9] {1,3}\. [0-9] {1,3}\. [0-9] {1,3}$ ]]; then        field1=$ (echo  $IP |cut -d.  -F1)         field2=$ (echo  $IP |cut -d. -f2)          field3=$ (echo  $IP |cut -d. -f3)          field4=$ (echo  $IP |cut -d. -f4)          if [  $FIELD 1 -le 255 -a  $FIELD 2 -le 255 -a   $FIELD 3 -le 255 -a  $FIELD 4 -le 255 ]; then             echo  "$IP  available."         else             echo  "$IP  not available!"         fi    else         echo  "$IP  not available!"     fi}# examplecheck_ip 192.168.1.1check_ip 256.1.1.1

Add a loop if the error is re-entered until it is correct:

Function check_ip ()  {    local ip=$1    valid_check=$ ( echo  $IP |awk -f.  ' $1<=255&&$2<=255&&$3<=255&&$4<=255{print   "Yes"} ')     if echo  $IP |grep -e  "^[0-9]{1,3}\. [0-9] {1,3}\. [0-9] {1,3}\. [0-9] {1,3}$ " >/dev/null; then        if [  $VALID _ check ==  "yes"  ]; then         echo  "$IP  available! "             return 0         else            echo  "$IP  not available!"             return 1         fi    else        echo  "$IP  not available!"         return 1    fi}while true;  do    read -p  "please enter ip: "  IP     check_ip  $IP     [ $? -eq 0 ] && break | |  continuedone

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Shell script determines whether IP is legitimate