Regex not matching correctly - javascript

Question

I am trying to implement a parser for systems of linear equations, so I want to match strings of the form:

2x + 3y = 5
55x + 34s + 9872v = 25

So, my regular expression is as follows:

/([0-9]+[a-z]\+{0,1})*=[0-9]+/;

However, it is matching incorrect expressions, such as:

23x + 50 = 35
36x + 5xg = 10

And I don't understand why, from what I can understand, it should only be a single digit (of any length) followed immediately by a single character, representing variable.

The pattern does not match anything there at all ATM due to the spaces. — CertainPerformance
– CertainPerformance, Commented Nov 18, 2019 at 6:06
May we ask what the ultimate goal here is? I mean, is all you want is to verify an expression, or do you, for example, want to extract components? — Tim Biegeleisen
– Tim Biegeleisen, Commented Nov 18, 2019 at 6:06

Karmveer Singh · Accepted Answer · 2019-11-18 07:07:50Z

3

Try below regex. Demo is here

(\d*(?<![a-z])[a-z][+-]?)+=\-?\d+

edited Nov 18, 2019 at 7:07

answered Nov 18, 2019 at 6:58

Karmveer Singh

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Comments

Mahbub Moon · Accepted Answer · 2019-11-18 07:03:41Z

0

You need to match the entire text, but the regex is returning any matching segment.

Modify your expression to /^([0-9]+[a-z]\+{0,1})*=[0-9]+$/, here the ^ and $ symbols are added to match entire string.

console.log("2x+3y=5".match(/^([0-9]+[a-z]\+{0,1})*=[0-9]+$/));
console.log("55x+34s+9872v=25".match(/^([0-9]+[a-z]\+{0,1})*=[0-9]+$/));
console.log("23x+50=35".match(/^([0-9]+[a-z]\+{0,1})*=[0-9]+$/));
console.log("36x+5xg=10".match(/^([0-9]+[a-z]\+{0,1})*=[0-9]+$/));

edited Nov 18, 2019 at 7:03

answered Nov 18, 2019 at 6:17

Mahbub Moon

5212 silver badges8 bronze badges

2 Comments

Perplexityy Over a year ago

I inputted 5x+5=5 into my program and it matched, when it shouldn't as there is no variable attached to the second number.

Karmveer Singh Over a year ago

@Perplexityy @Mahbub Moon x+2y=3 not matching and it's not working for -ve cases

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