How to represent greater than or equal 3600 in regex

Question

I wrote this regex to match numbers greater than or equal 3600. This is my attempt. However, I am not sure if it is complete:

grep -P '36[0-9]+[0-9]+[0-9]*' test.txt

I mean positive decimal integer numbers only (I do not need to consider floating, negative numbers, octal, hexadecimal, roman numerals...).

Solution 1

The extended regular expression ([1-9][0-9]{2,}|[4-9][0-9]|3[6-9])[0-9]{2} should do the job if you can be sure there are no negative numbers, floats, thousand limiters and so on around

The expression has three paths, all of which have in common the last part [0-9]{2}, which means two digits.

• First path is a 1 to 9 with at least two more digits ([0-9]{2,}) and those common twi digits, so it's all numbers with five or more digits: 10000 and above
• Second path is a 4 to 9 with three more digits: 4000 to 9999
• Third path is a 3 and something from 6 to 9 and those two digits. This matches everything between 3600 and 3999

Solution 2

Regex is not good comparing numbers !

Better use some scripting language. In your case awk would do a good job:

awk -F '[^0-9]*' '{for(i=1;i<=NF;i++){ if (int($i)>3600) { print; next; } }}' test.txt

Dependend on your input you should adapt this a bit.
My short example would e.g. not work correctly with negative numbers.

Comments

[Jeff Schaller]

Do you want to exclude a number like 3600.0?

[user9371654]

No floats, negatives or any kind of numbers mentioned by @Stéphane Chazelas. Just simple integers 2600, 3601, 3602, etc. They appear anywhere on the line.

[user9371654]

@Jeff Schaller No upper limit. Can you propose a fix?

[Angel Todorov]

Regular expressions are really the wrong hammer for this job.

[user9371654]

But you limit the number's length. How about this number: 31536000 or this: 31536000000?? Can you please explain your regex a bit?

[user9371654]

It does not capture this: 36000 although it is greater than 3600.

[user9371654]

I have tested it in 36000. It does not match the last zero. Only matches 3600 part. May be te last part in you regex should be [0-9]{2,} instead of [0-9]{2}??

[Angel Todorov]

You'll want to add anchors: \<(...)\>

[Philippos]

Sorry! The mistake was the order of the paths: When the first path generates a match (3600), the other paths are not checked anymore, so the longest match needs to be in the first path. I reordered the paths in my answer

[Stéphane Chazelas]

-P does left-to-right, but -E does longest.

[Stéphane Chazelas]

@glennjackman, anchors won't help in this case (note that it's \b with -P (or -w)) it would also mean it wouldn't match on 03600.