Shell Programming and Scripting

Regular Expression description

^([1-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])(\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])){3}$

Options: ^ and $ match at line breaks

Assert position at the beginning of a line (at beginning of the string or after a line break character)
Match the regular expression below and capture its match into backreference number 1 - ([1-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])
   Match either the regular expression below (attempting the next alternative only if this one fails) - [1-9]
      Match a single character in the range between "1" and "9" - [1-9]
   Or match regular expression number 2 below (attempting the next alternative only if this one fails) - [1-9][0-9]
      Match a single character in the range between "1" and "9" - [1-9]
      Match a single character in the range between "0" and "9" - [0-9]
   Or match regular expression number 3 below (attempting the next alternative only if this one fails) - 1[0-9][0-9]
      Match the character "1" literally - 1
      Match a single character in the range between "0" and "9" - [0-9]
      Match a single character in the range between "0" and "9" - [0-9]
   Or match regular expression number 4 below (attempting the next alternative only if this one fails) - 2[0-4][0-9]
      Match the character "2" literally - 2
      Match a single character in the range between "0" and "4" - [0-4]
      Match a single character in the range between "0" and "9" - [0-9]
   Or match regular expression number 5 below (the entire group fails if this one fails to match) - 25[0-5]
      Match the characters "25" literally - 25
      Match a single character in the range between "0" and "5" - [0-5]
Match the regular expression below and capture its match into backreference number 2 - (\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])){3}
   Exactly 3 times - {3}
   Note: You repeated the capturing group itself.  The group will capture only the last iteration.  Put a capturing group around the repeated group to capture all iterations. - {3}
   Match the character "." literally - \.
   Match the regular expression below and capture its match into backreference number 3 - ([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])
      Match either the regular expression below (attempting the next alternative only if this one fails) - [0-9]
         Match a single character in the range between "0" and "9" - [0-9]
      Or match regular expression number 2 below (attempting the next alternative only if this one fails) - [1-9][0-9]
         Match a single character in the range between "1" and "9" - [1-9]
         Match a single character in the range between "0" and "9" - [0-9]
      Or match regular expression number 3 below (attempting the next alternative only if this one fails) - 1[0-9][0-9]
         Match the character "1" literally - 1
         Match a single character in the range between "0" and "9" - [0-9]
         Match a single character in the range between "0" and "9" - [0-9]
      Or match regular expression number 4 below (attempting the next alternative only if this one fails) - 2[0-4][0-9]
         Match the character "2" literally - 2
         Match a single character in the range between "0" and "4" - [0-4]
         Match a single character in the range between "0" and "9" - [0-9]
      Or match regular expression number 5 below (the entire group fails if this one fails to match) - 25[0-5]
         Match the characters "25" literally - 25
         Match a single character in the range between "0" and "5" - [0-5]
Assert position at the end of a line (at the end of the string or before a line break character) - $