How to replace everything except 100 characters before and after a given string?

Question

I am trying to filter a set of data and I have to deal with multiple entries of ~5000 characters.

What I need is 100 characters before and after some keyword.

I have looked into regex code for search and replace but only found functions to get one keyword, not the surrounding characters.

Example Input:

abc123cde345fgh678ijk910keywordbc123cde345fgh678ijk910

Desired output with +-5 characters:

jk910keywordbc123

score 3 · Accepted Answer · answered Jun 02 '19 at 22:46

Match 100 characters, followed by the keyword, followed by 100 more characters:

const str = 'abc123cde345fgh678ijk910keywordbc123cde345fgh678ijk910';
const match = str.match(/.{5}keyword.{5}/);
console.log(match[0]);

If you need to construct the pattern dynamically, then:

const str = 'abc123cde345fgh678ijk910keywordbc123cde345fgh678ijk910';
const keyword = 'keyword';
const pattern = new RegExp(`.{5}${keyword}.{5}`);
const match = str.match(pattern);
console.log(match[0]);

If the pattern may contain characters with a special meaning in a regular expression, like $, then make sure to escape them first before passing to new RegExp:

// https://stackoverflow.com/questions/3561493/is-there-a-regexp-escape-function-in-javascript
const escape = s => s.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&');

const str = 'abc123cde345fgh678ijk910keyw$ordbc123cde345fgh678ijk910';
const keyword = 'keyw$ord';
const pattern = new RegExp(`.{5}${escape(keyword)}.{5}`);
const match = str.match(pattern);
console.log(match[0]);

score 0 · Answer 2 · answered Jun 03 '19 at 02:12

One solution for this can be implemented using String.indexOf() to search the index of the keyword inside the input string, and then use String.slice() to get the chars between a particular radius.

const str = 'abc123cde345fgh678ijk910keywordbc123cde345fgh678ijk910';

const getKeyword = (str, keyword, radius) =>
{
    let idx = str.indexOf(keyword);
    return str.slice(idx - radius, idx + keyword.length + radius);
}

console.log(getKeyword(str, "keyword", 5));
console.log(getKeyword(str, "keyword", 15));
console.log(getKeyword(str, "keyword", 1000));

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

Note this will also work when the radius is greater than the maximum possible, returning the entire string in this case.

How to replace everything except 100 characters before and after a given string?

2 Answers2