Validating IPv4 addresses with regexp

Question

I ve been trying to get an efficient regex for IPv4 validation  but without much luck  It seemed at one point I had had it with  25 0-5  2 0-4  0-9   01   0-9  0-9          4   but it produces some strange results     grep --version grep  GNU grep  2 7   grep -E   b 25 0-5  2 0-4  0-9   01   0-9  0-9          4  b   lt  lt  lt  192 168 1 1 192 168 1 1   grep -E   b 25 0-5  2 0-4  0-9   01   0-9  0-9          4  b   lt  lt  lt  192 168 1 255 192 168 1 255   grep -E   b 25 0-5  2 0-4  0-9   01   0-9  0-9          4  b   lt  lt  lt  192 168 255 255   grep -E   b 25 0-5  2 0-4  0-9   01   0-9  0-9          4  b   lt  lt  lt  192 168 1 2555 192 168 1 2555   I did a search to see if this had already been asked and answered  but other answers appear to simply show how to determine 4 groups of 1-3 numbers  or do not work for me

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With subnet mask         01    d  d  2 0-4   d 25 0-5        01    d  d  2 0-4   d 25 0-5        01    d  d  2 0-4   d 25 0-5        01    d  d  2 0-4   d 25 0-5        01    d  d  2 0-4   d 25 0-5

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mysql gt  select ip from foo where ip regexp     s  0-9      0-9      0-9      0-9   s

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25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0    4    This regex will not accept 08 8 8 8 or 8 08 8 8 or 8 8 08 8 or 8 8 8 08

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25 0-5  2 0-4  0-9   01   0-9  0-9          3    25 0-5  2 0-4  0-9   01   0-9  0-9          Above will be regex for the ip address like  221 234 000 112 also for 221 234 0 112  221 24 03 112  221 234 0 1    You can imagine all kind of address as above

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Try this    b   1-9   1-9  0-9  1 0-9  0-9  2 0-5  0-5      1-9   1-9  0-9  1 0-9  0-9  2 0-5  0-5      1-9   1-9  0-9  1 0-9  0-9  2 0-5  0-5     2 0-5  0-5  1 0-9  0-9   1-9  0-9   1-9    b

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-bash-3 2  echo  191 191 191 39    egrep          0-9    2  6-9  5 0-5    0-4  0-9     1  0-9  0-9      3-9  0-9   0    3        2  6-9  5 0-5    0-4  0-9     1  0-9  0-9      3-9  0-9   0      0-9       gt  gt  191 191 191 39   This is a DFA that matches the entire addr space  including broadcasts  etc   an nothing else

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ip address can be from 0 0 0 0 to 255 255 255 255     0 1   0-9  0-9   2 0-4  0-9  25 0-5       3   0 1   0-9  0-9   2 0-4  0-9  25 0-5      0 1   0-9  0-9   - checking value from 0 to 199 2 0-4  0-9 - checking value from 200 to 249 25 0-5 - checking value from 250 to 255     -- gt  represent verify   character   3  -- gt  will match exactly 3   -- gt  end of string

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This is regex works for me     lt     1-9  1 0-9   1-9  0-9  1 0-9  0-9  2 0-4  0-9  25 0-5      3   1-9  1 0-9   1-9  0-9  1 0-9  0-9  2 0-4  0-9  25 0-4     gt

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const char ipv4 regexp      b 25 0-5  2 0-4  0-9   01   0-9  0-9              25 0-5  2 0-4  0-9   01   0-9  0-9              25 0-5  2 0-4  0-9   01   0-9  0-9              25 0-5  2 0-4  0-9   01   0-9  0-9     b     I adapted the regular expression taken from JGsoft RegexBuddy library to C language  regcomp regexec  and I found out it works but there s a little problem in some OS like Linux  That regular expression accepts ipv4 address like 192 168 100 009 where 009 in Linux is considered an octal value so the address is not the one you thought  I changed that regular expression as follow       const char  ipv4 regex      b 25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9                    25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9                    25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9                    25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9    b     using that regular expressione now  192 168 100 009 is not a valid ipv4 address while 192 168 100 9 is ok   I modified a regular expression for multicast address too and it is the following       const char  mcast ipv4 regex      b 22 4-9  23 0-9                                 25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9                                 25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9                                  25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9    b     I think you have to adapt the regular expression to the language you re using to develop your application  I put an example in java       package utility       import java util regex Matcher      import java util regex Pattern       public class NetworkUtility            private static String ipv4RegExp      b      25 0-5  2 0-4   d 1  d  d  1-9    d       3    25 0-5  2 0-4   d 1  d  d  1-9    d    b            private static String ipv4MulticastRegExp    2   2 4-9  3  d          25 0-5  2 0-4   d 1  d  d  1-9   d  0   3             public NetworkUtility                         public static boolean isIpv4Address String address                Pattern pattern   Pattern compile ipv4RegExp               Matcher matcher   pattern matcher address                return matcher matches                       public static boolean isIpv4MulticastAddress String address                 Pattern pattern   Pattern compile ipv4MulticastRegExp                Matcher matcher   pattern matcher address                 return matcher matches

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Easy way     25 0-5  2 0-4  0-9   1  0-9  0-9   1-9  0-9  0 1      3  25 0-5  2 0-4  0-9   1  0-9  0-9   1-9  0-9  0 1     Demo

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I tried to make it a bit simpler and shorter           01   d 1 2  2 0-4  d 25 0-5      3   01   d 1 2  2 0-4  d 25 0-5      If you are looking for java kotlin          01    d 1 2  2 0-4   d 25 0-5       3   01    d 1 2  2 0-4   d 25 0-5      If someone wants to know how it works here is the explanation  It s really so simple  Just give it a try  p     1               is the starting and     is the ending    2      These are called a group  You can think of like  if  condition groups    3      Or  condition - as same as most of the programming languages    4   01   d 1 2     01   indicates one of the number between 0 and 1      means   01   is optional    d  is for any digit between 0-9 and   1 2   indicates the length can be between 1 and 2  So here the number can be 0-199    5  2 0-4  d   2  is just plain 2    0-4   means a number between 0 to 4    d  is for any digit between 0-9  So here the number can be 200-249    6  25 0-5    25  is just plain 25    0-5   means a number between 0 to 5  So here the number can be 250-255    7      It s just plan     dot  for separating the numbers    8   3   It means the exact 3 repetition of the previous group inside         9    01   d 1 2  2 0-4  d 25 0-5    Totally same as point 2-6   Mathematically it is like    0-199 OR 200-249 OR 250-255   Repeat exactly 3 times  0-199 OR 200-249 OR 250-255    So  as you can see normally this is the pattern for the IP addresses  I hope it helps to understand Regular Expression a bit   p

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I saw very bad regexes in this page   so i came with my own    b   d  1-9  d 1 d d 2 0-4  d 25 0-5      3   d  1-9  d 1 d d 2 0-4  d 25 0-5   b   Explanation   num-group    0-9 10-99 100-199 200-249 250-255   lt border gt       lt num-group gt     lt dot-cahracter gt   x3    lt num-group gt     lt border gt    Here you can verify how it works here

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Valid regex for IPV4 address for Java          d  1-9   d  0-1   d 2  2 0-4   d 25 0-5         3    d  1-9   d  0-1   d 2  2 0-4   d 25 0-5

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The most precise  straightforward and compact IPv4 regexp I can imagine is    25 0-5  2 0-4  d 1 d d  1-9   d    25 0-5  2 0-4  d 1 d d  1-9   d    25 0-5  2 0-4  d 1 d d  1-9   d    25 0-5  2 0-4  d 1 d d  1-9   d     But what about the performance efficiency of     Sorry I don t know  who cares

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String zeroTo255      0-9   0-9  0-9   0 1  0-9  0-9  2 0-4  0-9  25 0-5      it can contain single digit i e   0-9      It can contain two digits i e   0-9  0-9     range is  099 to 199 i e  0 1  0-9  0-9     range is  200 - 249  i e  2 0-9  0-9      range is  250-255  i e 25 0-5

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This one matches only valid IPs  no prepended 0 s  but it will match octets from 0-255 regardless of their  function   ie reserved  private  etc   and allows for inline matching  where there may be spaces before and or after the IP  or when using CIDR notation   grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5              grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   10 0 1 2  10 0 1 2    grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   ip address 10 0 1 2  ip address 10 0 1 2    grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   ip address 10 0 1 2 255 255 255 255  ip address 10 0 1 2 255 255 255 255    grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   ip address 10 0 1 2 32  ip address 10 0 1 2 32    grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   ip address 10 0 1 2 32       grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   ip address10 0 1 2       grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   10 0 1 256       grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   0 0 0 0  0 0 0 0    grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   255 255 255 255  255 255 255 255    grep -E           1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5       3   1-9   0-9  1 0-9  2  2 0-4  0-9  25 0-5            lt  lt  lt   255 255 255 256      Of course  in cases where the IP is inline  you can use grep option  -o  and your preference of whitespace trimmer if you just want the whole IP and nothing but the IP   For those of us using python  the equivalent is roughly    gt  gt  gt  ipv4 regex   re compile r           1-9   d 1 d 2  2 0-4  d 25 0-5      3     1-9   d 1 d 2  2 0-4  d 25 0-5             gt  gt  gt  ipv4 regex search  ip address 10 1 2 3 32    lt re Match object  span  10  20   match   10 1 2 3   gt    If you re picky  lazy  like me  you probably would prefer to use grouping to get the whole IP and nothing but the IP  or the CIDR and nothing but the CIDR or some combination thereof  We can use   P  syntax to name our groups for easier reference    gt  gt  gt  ipv4 regex   re compile r          P lt address gt      1-9   d 1 d 2  2 0-4  d 25 0-5      3     1-9   d 1 d 2  2 0-4  d 25 0-5     P lt slash gt       slash   P lt cidr gt  0-9   12  0-9  3 0-2              gt  gt  gt  match   ipv4 regex search  ip address 10 0 1 2 32    gt  gt  gt  match group  address    10 0 1 2   gt  gt  gt  match group  cidr    32   gt  gt  gt     join  match group  address    match group  slash    match group  cidr      10 0 1 2 32    There s ways of not using just regex  of course  Here s some conditions that you could check  this one doesn t find inline  just validates the passed address is valid    First check is that each char in the address is a digit or a      Next checking that there are exactly 3      The next two checks check that each octet is between 0 and 255    And the last check is that no octets are prepended with a  0   def validate ipv4 address address       return all re match      d   c  for c in address            and address count         3           and all 0  lt   int octet   lt   255 for octet in address split                 and all  len bin int octet     lt   10 for octet in address split                  and all len octet     1 or d 0      0  for octet in address split          gt  gt  gt  validate ipv4 address  255 255 255 255   True  gt  gt  gt  validate ipv4 address  10 0 0 1   True  gt  gt  gt  validate ipv4 address  01 01 01 01   False  gt  gt  gt  validate ipv4 address  123 456 789 0   False  gt  gt  gt  validate ipv4 address  0 0 0 0   True  gt  gt  gt  validate ipv4 address  -1 0 0 0   False  gt  gt  gt  validate ipv4 address  1 1 1    Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 4  in validate ipv4 address   File   lt stdin gt    line 4  in  lt genexpr gt  ValueError  invalid literal for int   with base 10      gt  gt  gt  validate ipv4 address   1 1 1   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 4  in validate ipv4 address   File   lt stdin gt    line 4  in  lt genexpr gt  ValueError  invalid literal for int   with base 10      gt  gt  gt  validate ipv4 address  1  1 1   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 4  in validate ipv4 address   File   lt stdin gt    line 4  in  lt genexpr gt  ValueError  invalid literal for int   with base 10        bitwise  each octet should be 8 bits or less  but each is prepended with  0b     gt  gt  gt  bin 0   0b0   gt  gt  gt  len bin 0   3  gt  gt  gt  bin 255   0b11111111   gt  gt  gt  len bin 256   11

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Following is the regex expression to validate the IP-Address       25 0-5  2 0-4  0-9   01   0-9  0-9        3  25 0-5  2 0-4  0-9   01   0-9  0-9

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IPv4 address is a very complicated thing   Note  Indentation and lining are only for illustration purposes and do not exist in the real RegEx    b            2 5 0-5   0-4  0-9   1 0-9  2   1-9   0-9           0 Xx 0  0-9A-Fa-f  1 2          0  1-3   0-9  1 2         1 3           2 5 0-5   0-4  0-9   1 0-9  2   1-9   0-9           0 Xx 0  0-9A-Fa-f  1 2          0  1-3   0-9  1 2                 1-3  0-9  1 9           1-9  0-9   8           4  0-1  0-9  8         2  0-8  0-9  7           9  0-3  0-9  6             4  0-8  0-9  5               9  0-5  0-9  4                 6  0-6  0-9  3                   7  0-1  0-9  2                     2  0-8  0-9  1                       9  0-5                         0 Xx 0  0-9A-Fa-f  1 8      0  1-3   0-7   10    b   These IPv4 addresses are validated by the above RegEx    127 0 0 1 2130706433 0x7F000001 017700000001 0x7F 0 0 01   Mixed hex dec oct 000000000017700000001   Have as many leading zeros as you want 0x0000000000007F000001   Same as above 127 1 127 0 1   These are rejected   256 0 0 1 192 168 1 099   099 is not a valid number 4294967296   UINT32 MAX   1 0x100000000 020000000000

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I would use PCRE and the define keyword            amp byte        amp byte        amp byte        amp byte        DEFINE          lt byte gt 25 0-5  2 0-4  d  01   d d     gmx   Demo  https   regex101 com r IB7j48 2  The reason of this is to avoid repeating the  25 0-5  2 0-4  0-9   01   0-9  0-9    pattern four times  Other solutions such as the one below work well  but it does not capture each group as it would be requested by many        d           4      The only other way to have 4 capture groups is to repeat the pattern four times         lt one gt  d       lt two gt  d       lt three gt  d       lt four gt  d       Capturing a ipv4 in perl is therefore very easy     echo  Hey this is my IP address 138 131 254 8  bye         perl -ne  print    1   2   3   4   if         b    amp byte        amp byte        amp byte        amp byte           DEFINE           b   lt byte gt 25 0-5  2 0-4  0-9   01   0-9  0-9          x    138  131  254  8

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IPv4 address  accurate capture  Matches 0 0 0 0 through 255 255 255 255  but does capture invalid addresses such as 1 1 000 1 Use this regex to match IP numbers with accuracy  Each of the 4 numbers is stored into a capturing group  so you can access them for further processing   b  25 0-5  2 0-4  0-9   01   0-9  0-9       25 0-5  2 0-4  0-9   01   0-9  0-9       25 0-5  2 0-4  0-9   01   0-9  0-9       25 0-5  2 0-4  0-9   01   0-9  0-9     b  taken from JGsoft RegexBuddy library Edit  this        part seems weird

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25 0-5  2 0-4  d 1 d d  1-9  d  d     3   1   m

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For number from 0 to 255 I use this regex        0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5      Above regex will match integer number from 0 to 255  but not match 256     So for IPv4 I use this regex         0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5          0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5     3      It is in this structure    N      N   3    where N is the regex used to match number from 0 to 255  This regex will match IP like below     0 0 0 0 192 168 1 2   but not those below     10 1 0 256 1 2 3  127 0 1-2 3   For IPv4 CIDR  Classless Inter-Domain Routing  I use this regex         0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5          0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5     3       0-9     12  0-9    3 0-2       It is in this structure    N      N   3    M  where N is the regex used to match number from 0 to 255  and M is the regex used to match number from 0 to 32  This regex will match CIDR like below     0 0 0 0 0 192 168 1 2 32   but not those below     10 1 0 256 16 1 2 3  24 127 0 0 1 33   And for list of IPv4 CIDR like  10 0 0 0 16    192 168 1 1 32  I use this regex           0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5          0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5     3       0-9     12  0-9    3 0-2                   0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5          0-9     1-9  0-9    1  0-9  2     2 0-4  0-9    25 0-5     3       0-9     12  0-9    3 0-2            It is in this structure       C                 C         where C is the regex used to match CIDR  like 0 0 0 0 0   This regex will match list of CIDR like below        10 0 0 0 16       192 168 1 2 32        1 2 3 4 32      but not those below        10 0 0 0 16    192 168 1 2 32    1 2 3 4 32      Maybe it might get shorter but for me it is easy to understand so fine by me     Hope it helps

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I found this sample very useful  furthermore it allows different ipv4 notations   sample code using python       def is valid ipv4 ip4          Validates IPv4 addresses              import re     pattern   re compile r                                      Dotted variants                              Decimal 1-255  no leading 0 s               3-9  d  2   5 0-5   0-4   d   1 d 0 2                          0x0  0-9a-f  1 2     Hexadecimal 0x0 - 0xFF  possible leading 0 s                          0  1-3   0-7  0 2    Octal 0 - 0377  possible leading 0 s                                               Repeat 0-3 times  separated by a dot                                               3-9  d  2   5 0-5   0-4   d   1 d 0 2                              0x0  0-9a-f  1 2                              0  1-3   0-7  0 2                            0 3                      0x0  0-9a-f  1 8       Hexadecimal notation  0x0 - 0xffffffff                     0  0-3   0-7  0 10     Octal notation  0 - 037777777777                       Decimal notation  1-4294967295            429496729 0-5  42949672 0-8  d 4294967 01  d d 429496 0-6  d 3             42949 0-5  d 4  4294 0-8  d 5  429 0-3  d 6  42 0-8  d 7             4 01  d 8   1-3  d 0 9   4-9  d 0 8                               re VERBOSE   re IGNORECASE      return pattern match ip4   lt  gt  None

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Newest  shortest  least readable version  55 chars      25 0-5   2 0-4  1 0-9   1-9    0-9               4    This version looks for the 250-5 case  after that it cleverly ORs all the possible cases for 200-249 100-199 10-99 cases  Notice that the    part is not a mistake  but actually ORs the last case for the 0-9 range  I ve also omitted the    non-capturing group part as we don t really care about the captured items  they would not be captured either way if we didn t have a full-match in the first place   Old and shorter version  less readable   63 chars        25 0-5  2 0-4  0-9  1 0-9  2   1-9   0-9               4    Older  readable  version  70 chars        25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9               4    It uses the negative lookahead      to remove the case where the ip might end with a    Oldest answer  115 chars          25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9      3         25 0-5  2 0-4  0-9  1 0-9  0-9   1-9  0-9   0-9      I think this is the most accurate and strict regex  it doesn t accept things like 000 021 01 0  it seems like most other answers here do and require additional regex to reject cases similar to that one - i e  0 starting numbers and an ip that ends with a

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Finds a valid IP addresses as long as the IP is wrapped around any character other than digits  behind or ahead the IP   4 Backreferences created     first     second     third     forth   Find String   any valid IP address    lt IP gt    lt    d     lt first gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt second gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt third gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt forth gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5        d     only valid private IP address RFC1918    lt IP gt    lt    d           lt first gt 10        lt second gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5           lt first gt 172        lt second gt    1 6-9      2 0-9      3 0-1           lt first gt 192        lt second gt 168          lt third gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt forth gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5        d     Notepad   Replace String Option 1  Replaces the whole IP  NO Change      IP   Notepad   Replace String Option 2  Replaces the whole IP octect by octect  NO Change     first     second     third     forth   Notepad   Replace String Option 3  Replaces the whole IP octect by octect  replace 3rd octect value with 0     first     second  0    forth  NOTE  The above will match any valid IP including 255 255 255 255 for example and change it to 255 255 0 255 which is wrong and not very useful of course    Replacing portion of each octect with an actual value however you can build your own find and replace which is actual useful to ammend IPs in text files   for example replace the first octect group of the original Find regex above     lt first gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5    with    lt first gt 10   and    lt second gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5    with    lt second gt 216  and you are now matching addresses starting with first octect 192 only  Find on notepad       lt IP gt    lt    d     lt first gt 10        lt second gt 216        lt third gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt forth gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5        d      You could still perform Replace using back-referece groups in the exact same fashion as before   You can get an idea of how the above matched below   cat ipv4 validation test txt Full Match  0 0 0 1 12 108 1 34 192 168 1 1 10 249 24 212 10 216 1 212 192 168 1 255 255 255 255 255 0 0 0 0   Partial Match  IP Extraction from line  30 168 1 0 1 -1 2 3 4 sfds10 216 24 23kgfd da11 15 112 255adfdsfds sfds10 216 24 23kgfd   NO Match 1 1 1 01 3   3 127 1  192 168 1   192 168 1 256 da11 15 112 2554adfdsfds da311 15 112 255adfdsfds   Using grep you can see the results below   From grep  grep -oP     lt IP gt    lt    d     lt first gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt second gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt third gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt forth gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5        d     ipv4 validation test txt 0 0 0 1 12 108 1 34 192 168 1 1 10 249 24 212 10 216 1 212 192 168 1 255 255 255 255 255 0 0 0 0 30 168 1 0 1 2 3 4 10 216 24 23 11 15 112 255 10 216 24 23   grep -P     lt IP gt    lt    d     lt first gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt second gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt third gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt forth gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5        d     ipv4 validation test txt 0 0 0 1 12 108 1 34 192 168 1 1 10 249 24 212 10 216 1 212 192 168 1 255 255 255 255 255 0 0 0 0 30 168 1 0 1 -1 2 3 4 sfds10 216 24 23kgfd da11 15 112 255adfdsfds sfds10 216 24 23kgfd    matching ip addresses starting with 10 216 grep -oP     lt IP gt    lt    d     lt first gt 10        lt second gt 216        lt third gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5          lt forth gt     d      1-9  d     1 d 2      2 0-4  d     25 0-5        d     ipv4 validation test txt 10 216 1 212 10 216 24 23 10 216 24 23

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I was in search of something similar for IPv4 addresses - a regex that also stopped commonly used private ip addresses from being validated  192 168 x y  10 x y z  172 16 x y  so used negative look aheads to accomplish this       10   172   1 6-9  2 d 3 01     192  168          255  255  255  255  25 0-5  2 0-4  d  1  d d  1-9  d  1-9       25 0-5  2 0-4  d  1  d d  1-9  d  d   3     These should be on one line of course  formatted for readability purposes on 3 separate lines    Debuggex Demo  It may not be optimised for speed  but works well when only looking for  real  internet addresses   Things that will  and should  fail   0 1 2 3          0 0 0 0 8 is reserved for some broadcasts  10 1 2 3         10 0 0 0 8 is considered private  172 16 1 2       172 16 0 0 12 is considered private  172 31 1 2       same as previous  but near the end of that range  192 168 1 2      192 168 0 0 16 is considered private  255 255 255 255  reserved broadcast is not an IP   2 3 4 1 2 3  1 2 3 256 1 2 256 4 1 256 3 4 256 2 3 4 1 2 3 4 5 1  3 4   IPs that will  and should  work   1 0 1 0          China  8 8 8 8          Google DNS in USA  100 1 2 3        USA  172 15 1 2       USA  172 32 1 2       USA  192 167 1 2      Italy    Provided in case anybody else is looking for validating  Internet IP addresses not including the common private addresses

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My  extended  approach   regexp for space-separated IP addresses      25 0-5   2 0-4  1 0-9   1-9    0-9           d       d    4               Uses PCRE look-ahead

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I think many people reading this post will be looking for simpler regular expressions  even if they match some technically invalid IP addresses   And  as noted elsewhere  regex probably isn t the right tool for properly validating an IP address anyway    Remove   and  where applicable  replace   with  b  if you don t want to match the beginning end of the line   Basic Regular Expression  BRE   tested on GNU grep  GNU sed  and vim       0-9      0-9      0-9      0-9        Extended Regular Expression  ERE       0-9     0-9     0-9     0-9       or       0-9          4     Perl-compatible Regular Expression  PCRE   tested on Perl 5 18       d    d    d    d      or       d         4     Ruby  tested on Ruby 2 1    Although supposed to be PCRE  Ruby for whatever reason allowed this regex not allowed by Perl 5 18       d        4     My tests for all these are online here

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25 0-5  2 0-4  0-9   01   0-9  0-9       3  25 0-5  2 0-4  0-9   01   0-9  0-9      Accept  127 0 0 1 192 168 1 1 192 168 1 255 255 255 255 255 0 0 0 0 1 1 1 01          This is an invalid IP address   Reject  30 168 1 255 1 127 1 192 168 1 256 -1 2 3 4 1 1 1 1  3   3  Try online with unit tests  https   www debuggex com r -EDZOqxTxhiTncN6 1

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This is a little longer than some but this is what I use to match IPv4 addresses  Simple with no compromises      25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9      3  25 0-5  2 0-4  0-9  1 0-9  0-9   1-9   0-9

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I think this one is the shortest       01   d d  2 0-4  d 25 0-5     3   01   d d  2 0-4  d 25 0-5

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I managed to construct a regex from all other answers    25 0-5  2 0-4  0-9   1  0-9  0-9   1-9  0-9   0-9       25 0-5  2 0-4  0-9   1  0-9  0-9   1-9  0-9   0-9     3

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Above answers are valid but what if the ip address is not at the end of line and is in between text   This regex will even work on that    code    b    0-9   1-9  0-9  1 0-9  2  2 0-4  0-9  25 0-5        3   0-9   1-9  0-9  1 0-9  2  2 0-4  0-9  25 0-5    b   input text file   ip address 0 0 0 0 asfasf  sad sa 255 255 255 255 cvjnzx zxckjzbxk  999 999 999 999 jshbczxcbx sjaasbfj 192 168 0 1 asdkjaksb oyo 123241 24121 1234 3423 yo yo 0000 0000 0000 0000 y aw1a 21asd2 21ad 21d2 yo 254 254 254 254 y0 172 24 1 210 asfjas 200 200 200 200 000 000 000 000 007 08 09 210 010 10 30 110   output text   0 0 0 0 255 255 255 255 192 168 0 1 254 254 254 254 172 24 1 210 200 200 200 200

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You ve already got a working answer but just in case you are curious what was wrong with your original approach  the answer is that you need parentheses around your alternation otherwise the        is only required if the number is less than 200     b  25 0-5  2 0-4  0-9   01   0-9  0-9           4  b

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This code works for me  and is as simple as that   Here I have taken the value of ip and I am trying to match it with regex   ip  25 255 45 67       op re match    d     d     d     d    ip   if   int op group 1   lt  255  and  int op group 2   lt  255  and int op group 3   lt  255  and  int op group 4   lt  255     print  valid ip    else   print  Not valid     Above condition checks if the value exceeds 255 for all the 4 octets then it is not a valid  But before applying the condition we have to convert them into integer since the value is in a string   group 0  prints the matched output  Whereas group 1  prints the first matched value and here it is  25  and so on

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25 0-5    2 0-4  d   1 d 2     d 1 2       3    25 0-5    2 0-4  d   1 d 2     d 1 2       Test to find matches in text  https   regex101 com r 9CcMEN 2  Following are the rules defining the valid combinations in each number of an IP address    Any one- or two-digit number  Any three-digit number beginning with 1  Any three-digit number beginning with 2 if the second digit is 0 through 4  Any three-digit number beginning with 25 if the third digit is 0 through 5    Let start with    25 0-5    2 0-4  d   1 d 2     d 1 2        a set of four nested subexpressions  and we   ll look at them in reverse order    d 1 2   matches any one- or two-digit number or numbers 0 through 99   1 d 2   matches any three-digit number starting with 1  1 followed by any two digits   or numbers 100 through 199   2 0-4  d  matches numbers 200 through 249   25 0-5   matches numbers 250 through 255  Each of these subexpressions is enclosed within another subexpression with an   between each  so that one of the four subexpressions has to match  not all   After the range of numbers comes    to match    and then the entire series  all the number options plus     is enclosed into yet another subexpression and repeated three times using  3   Finally  the range of numbers is repeated  this time without the trailing     to match the final IP address number  By restricting each of the four numbers to values between 0 and 255  this pattern can indeed match valid IP addresses and reject invalid addresses      Excerpt From  Ben Forta     Learning Regular Expressions         If neither a character is wanted at the beginning of IP address nor at the end    and   metacharacters ought to be used  respectively       25 0-5    2 0-4  d   1 d 2     d 1 2       3    25 0-5    2 0-4  d   1 d 2     d 1 2        Test to find matches in text  https   regex101 com r uAP31A 1

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I tried to make it a bit simpler and shorter          01   d 1 2  2 0-4  d 25 0-5     3   01   d 1 2  2 0-4  d 25 0-5      If you are looking for java kotlin          01   d 1 2  2 0-4  d 25 0-5      3   01   d 1 2  2 0-4  d 25 0-5      If someone wants to know how it works here is the explanation  It s really so simple  Just give it a try  p     1               is the starting and     is the ending    2      These are called a group  You can think of like  if  condition groups    3      Or  condition - as same as most of the programming languages    4   01   d 1 2     01   indicates one of the number between 0 and 1      means   01   is optional    d  is for any digit between 0-9 and   1 2   indicates the length can be between 1 and 2  So here the number can be 0-199    5  2 0-4  d   2  is just plain 2    0-4   means a number between 0 to 4    d  is for any digit between 0-9  So here the number can be 200-249    6  25 0-5    25  is just plain 25    0-5   means a number between 0 to 5  So here the number can be 250-255    7      It s just plan     dot  for separating the numbers    8   3   It means the exact 3 repetition of the previous group inside         9    01   d 1 2  2 0-4  d 25 0-5    Totally same as point 2-6   Mathematically it is like    0-199 OR 200-249 OR 250-255   Repeat exactly 3 times  0-199 OR 200-249 OR 250-255    So  as you can see normally this is the pattern for the IP addresses  I hope it helps to understand Regular Expression a bit   p

[regex] Validating IPv4 addresses with regexp

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