I would like to create a regex that will validate that a string is an equation made up of a single digits and either the * or + operator and is no longer than 100 characters. So these would be valid:
1+2*3*8+0
9
9*9
And these would not be valid:
1++1
12+1
2*25
1+
47
+
+1
11
I came up with the regex below to accomplish this:
^(\d{1}[\+\*]{1}){0,99}\d$
Which appears to work, but I'm curious if there is a cleaner way to accomplish this. Any suggestions or is this about as clean as it gets?
It is saved here if you would like to play with it.
2 Answers 2
- While your regex appears to work, it will fail for the condition that your expression should not exceed 100 characters mark. With the boundary of
{0,99}on a 2 character pattern\d{1}[\*\+]{1}, you are already expecting a possible expression of length 198 characters. - Using
{1}quantifier is just redundant. - No need for escaping inside a character set. The only things needing a leading backslash (
\) inside a characters list are]and^, where the caret is the only character inside, or the first. - Your expressions will not reach a 100 character mark, unless you allow the
+to act as an unary operator.
Therefore, the following pattern will be the simplest approach (imo)
^(?:\d[*+]){0,49}\d$
which is the tiniest bit modified from your original expression.
You can check the pattern in action here on the following expressions:
1+2*3*8+0
9
9*9
1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+5*8
1++1
12+1
2*25
1+
47
+
+1
11
1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+1*2+5*8+9
Explicit length check for clarity
You checked the length of the string inside the regular expression, it was not obvious and @hjpotter92 found a bug in it. His fix uses half of the desired length inside the regexp making it even less intuitive.
I suggest using as a regexp ^(?:\d[*+])*\d$ and checking the length separately.