Bash script - not able to validate ip

And for a real answer now, if you want to check for IPv4 addresses using only bash, you have to use a slightly more complex regex. I use an intermediate variable here to keep the things understandable:

BYTE='((0*1?[0-9]?[0-9])|(2[0-4][0-9])|(25[0-5]))'
#      ^^^^^^^^^^^^^^^^^                           matches 0-199 (with optional leading zeros
#                        ^^^^^^^^^^^^^             matches 200-249
#                                      ^^^^^^^^^   matches 250-255
if [[ $ip =~ ^$BYTE\.$BYTE\.$BYTE\.$BYTE$ ]]
then
    # ...
else
    # ...
fi

I think you are using . instead of \.

the following script should do what you want:

#!/bin/bash
read -p "enter your value" ip
if [[ $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]
   then
     echo "valid"
   else
     echo "invalid"
fi

If you want more advanced script actually checking the scope of the numbers given you could look into this linux journal article.

This is more a comment than a real answer but...

# _your_ regex:
sh$ [[ 923.34442.123 =~ ^[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}$ ]] && echo ok || echo notok
ok

# regex using backslash:
sh$ [[ 23.34442.123 =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]] && echo ok || echo notok
notok

As this has already been explained, the key point is the use of the backslash (\). The dot (.) alone will match any single character. The [0-9]{1,3} part means "match any sequence of 1 to 3 digit".

So, broadly speaking, your regex would match any string having 4 sequences of 1 to 3 digits separated by any char:

9  2  3  .  3  4  4  4  2  .  1  2  3

d  d  d  a  d  d  d  a  d  a  d  d  d
i  i  i  n  i  i  i  n  i  n  i  i  i
g  g  g  y  g  g  g  y  g  y  g  g  g
i  i  i  c  i  i  i  c  i  c  i  i  i
t  t  t  h  t  t  t  h  t  h  t  t  t
         a           a     a
         r           r     r

It might be surprising at first, but it matches...

As a side note, even the "backslash-dot regex" will accept non valid IPv4 addresses: for example 923.34.42.123 would match, but is obviously incorrect. So for fun here is an awk based filter (and its test set) to remove invalid IPv4 addresses from a listing. Feel free to adapt to your needs (or ignore it completely;)

sh$ BYTE='[0-2]?[0-9]?[0-9]' # Might even be BYTE='0*[0-2]?[0-9]?[0-9]'
sh$ cat << EOF | awk -v FS='.' "/^$BYTE\.$BYTE\.$BYTE\.$BYTE$/"' {
                                   if (($1<= 255)&&($2<=255)&&($3<=255)&&($4<=255))
                                      print $0 }'              
4.2.2.2
a.b.c.d
192.168.1.1
0.0.0.0
255.255.255.255
255.255.255.256
192.168.0.1
192.168.0
1234.123.123.123
EOF

And here is the result:

4.2.2.2
192.168.1.1
0.0.0.0
255.255.255.255
192.168.0.1

Thanks for reply finally i found a solution

if [[ $ip =~ '^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$' ]]

i was not using single quote.