Regular Expression (regex) for a number greater than 1200

Posted written by Paul Seal on August 19, 2016 Regex

I don't know about you, but I find regluar expressions quite difficult. Apart from a very simple, I almost always have to look it up or use a reference book.

Yesterday, one of my colleagues needed a regex for filtering on Google Analytics. The value needed to be greater than 1200 to be valid.

In case you are looking for a regex for something similar, I though I would post it so you can alter it for your needs.

Regex greater than 1200

^[1-9][2-9](?!00$)[0-9][1-9]?\d+$

I used this tool to test it.

And this is the tool's English interpretation of what the regex is doing:

  • ^ assert position at start of the string
  • [1-9] match a single character present in the list below
    • 1-9 a single character in the range between 1 and 9
  • [2-9] match a single character present in the list below
    • 2-9 a single character in the range between 2 and 9
  • (?!00$) Negative Lookahead - Assert that it is impossible to match the regex below
    • 00 matches the characters 00 literally
    • $ assert position at end of the string
  • [0-9] match a single character present in the list below
    • 0-9 a single character in the range between 0 and 9
  • [1-9]? match a single character present in the list below
    • Quantifier: ? Between zero and one time, as many times as possible, giving back as needed [greedy]
    • 1-9 a single character in the range between 1 and 9
  • \d+ match a digit [0-9]
    • Quantifier: + Between one and unlimited times, as many times as possible, giving back as needed [greedy]
  • $ assert position at end of the string
  • 1-9 a single character in the range between 1 and 9
  • 2-9 a single character in the range between 2 and 9
  • 00 matches the characters 00 literally
  • $ assert position at end of the string
  • 0-9 a single character in the range between 0 and 9
  • Quantifier: ? Between zero and one time, as many times as possible, giving back as needed [greedy]
  • 1-9 a single character in the range between 1 and 9
  • Quantifier: + Between one and unlimited times, as many times as possible, giving back as needed [greedy]

Summary

The key part to this is the look ahead (?!00$), this makes sure that it won't end with 00 after the first 2 digits. Without this in there, it would say 1200 is valid, which violates the rule of greater than

Anyway, I hope someone finds this useful one day. Or me 6 months time when I've forgotten and need something similar.