[regex] Regex: ignore case sensitivity

How can I make the following regex ignore case sensitivity? It should match all the correct characters but ignore whether they are lower or uppercase.

G[a-b].*

[gG][aAbB].* probably simples solution if the pattern is not too complicated or long.

JavaScript

If you want to make it case insensitive just add i at the end of regex:

'Test'.match(/[A-Z]/gi) //Returns ["T", "e", "s", "t"]

Without i

'Test'.match(/[A-Z]/g) //Returns ["T"]

Addition to the already-accepted answers:

Grep usage:

Note that for greping it is simply the addition of the -i modifier. Ex: grep -rni regular_expression to search for this 'regular_expression' 'r'ecursively, case 'i'nsensitive, showing line 'n'umbers in the result.

Also, here's a great tool for verifying regular expressions: https://regex101.com/

Ex: See the expression and Explanation in this image.

References:

• man pages (man grep)
• http://droptips.com/using-grep-and-ignoring-case-case-insensitive-grep

In JavaScript you should pass the i flag to the RegExp constructor as stated in MDN:

const regex = new RegExp('(abc)', 'i');

regex.test('ABc'); // true

As I discovered from this similar post (ignorecase in AWK), on old versions of awk (such as on vanilla Mac OS X), you may need to use 'tolower($0) ~ /pattern/'.

IGNORECASE or (?i) or /pattern/i will either generate an error or return true for every line.

C#

using System.Text.RegularExpressions;
...    
Regex.Match(
    input: "Check This String",
    pattern: "Regex Pattern",
    options: RegexOptions.IgnoreCase)

specifically: options: RegexOptions.IgnoreCase

The i flag is normally used for case insensitivity. You don't give a language here, but it'll probably be something like /G[ab].*/i or /(?i)G[ab].*/.

You also can lead your initial string, which you are going to check for pattern matching, to lower case. And using in your pattern lower case symbols respectively .

Just for the sake of completeness I wanted to add the solution for regular expressions in C++ with Unicode:

std::tr1::wregex pattern(szPattern, std::tr1::regex_constants::icase);

if (std::tr1::regex_match(szString, pattern))
{
...
}

You can practice Regex In Visual Studio and Visual Studio Code using find/replace.

You need to select both Match Case and Regular Expressions for regex expressions with case. Else [A-Z] won't work.enter image description here

In Java, Regex constructor has

Regex(String pattern, RegexOption option)

So to ignore cases, use

option = RegexOption.IGNORE_CASE

Depends on implementation but I would use

(?i)G[a-b].

VARIATIONS:

(?i) case-insensitive mode ON    
(?-i) case-insensitive mode OFF

Modern regex flavors allow you to apply modifiers to only part of the regular expression. If you insert the modifier (?im) in the middle of the regex then the modifier only applies to the part of the regex to the right of the modifier. With these flavors, you can turn off modes by preceding them with a minus sign (?-i).

Description is from the page: https://www.regular-expressions.info/modifiers.html

regular expression for validate 'abc' ignoring case sensitive

(?i)(abc)