Edit

6 years after my original answer (below) I would solve this problem differently

function mreplace (replacements, str) {
  let result = str;
  for (let [x, y] of replacements)
    result = result.replace(x, y);
  return result;
}

let input = 'Hello World what a beautiful day';

let output = mreplace ([
  [/Hello/, 'Bye'],
  [/World/, 'Universe']
], input);

console.log(output);
// "Bye Universe what a beautiful day"

This has as tremendous advantage over the previous answer which required you to write each match twice. It also gives you individual control over each match. For example:

function mreplace (replacements, str) {
  let result = str;
  for (let [x, y] of replacements)
    result = result.replace(x, y);
  return result;
}

let input = 'Hello World what a beautiful day';

let output = mreplace ([
  //replace static strings
  ['day', 'night'],
  // use regexp and flags where you want them: replace all vowels with nothing
  [/[aeiou]/g, ''],
  // use captures and callbacks! replace first capital letter with lowercase 
  [/([A-Z])/, 0.toLowerCase()]

], input);

console.log(output);
// "hll Wrld wht  btfl nght"

Original answer

Andy E's answer can be modified to make adding replacement definitions easier.

var text = "Hello World what a beautiful day";
text.replace(/(Hello|World)/g, function ($0){
  var index = {
    'Hello': 'Bye',
    'World': 'Universe'
  };
  return index[$0] != undefined ? index[0;
});

// "Bye Universe what a beautiful day";

First, since you already did so inside of your two last expressions, with the same replacement:

article = article.replace(/\r?\n|\r/g,"")
article = article.replace(/\$|\#|\[|\]/g, "")

I'm puzzled why you didn't simply put both in a unique regexp:

article = article.replace(/\r?\n|\r|\$|\#|\[|\]/g, "")

Then to integrate with the 1st one, you might choose to:

• join the two distincts replacements in a single line:

  var article = a.replace(/ |\./g, "_").replace(/\r?\n|\r|\$|\#|\[|\]/g, "")
  

• or use a map approach, either suche the one pointed by @greybeard's link, or like this way (even if it might look a bit too sohpisticated for only two cases):

  var replacements = new Map([
      [/ |\./g, '_'],
      [/\r?\n|\r|\$|\#|\[|\]/g, '']
      ]),
      article = a;
  replacements.forEach(function(value, key){
        article = article.replace(key, value);
      });
  

The most interesting aspect in this latter solution is that it may be easily expanded if more replacements are needed.

EDIT following a good suggestion from @Niet the Dark Absol.

As soon as there are several unique characters to look for, with the same replacement, this kind of regexp /(a|b|c)/ can be replaced by /[abc]/, which is both simpler and more efficient!

Any of the above proposed solutions can be improved this way, so the latter one becomes:

    var replacements = new Map([
        [/[ .]/g, '_'],
        [/[\r\n$#[\]]/g, '']
        ]),
        article = a;
    replacements.forEach(function(value, key){
          article = article.replace(key, value);
        });

I think that you can use two replaces, or:

string sample = "Print Computer information";
string result = Regex.Replace( sample, @"(Print )(.*)( information)", "$1a $2 operation$3" );

For ignorecase you need to use re.I or re.IGNORECASE

Try with this code:

import re

regexes = {
    r'\s(\(|\[)(.*?)Mix(.*?)(\)|\])' : r"",
    r'\s(\(|\[)(.*?)Version(.*?)(\)|\])' : r"",
    r'\s(\(|\[)(.*?)Remix(.*?)(\)|\])' : r"",
    r'\s(\(|\[)(.*?)Extended(.*?)(\)|\])' : r"",
    r'\s\(remix\)' : r"",
    r'\s\(original\)' : r"",
    r'\s\(intro\)' : r"",
}

def multi_replace(dict, text):
    for key, value in dict.items():
        p = re.compile(key, re.I)
        text = p.sub(value, text)
    return text

filename = "Testing (Intro)"

name = multi_replace(regexes, filename)

print(name)

Use a Match evaluator inside the Regex.Replace:

var pattern = @"\$\$\@[a-zA-Z0-9_]*\b";
var stringVariableMatches = Regex.Replace(strValue, pattern, 
        m => variablesDictionary[m.Value]);

The Regex.Replace method will perform global replacements, i.e. will search for all non-overlapping substrings that match the indicated pattern, and will replace each found match value with the variablesDictionary[m.Value].

Note that it might be a good idea to check if the key exists in the dictionary.

See a C# demo:

using System;
using System.IO;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Linq;
public class Test
{
    public static void Main()
    {
        var variablesDictionary = new Dictionary<string, string>();
        variablesDictionary.Add("$$@Key", "Value");
        var pattern = @"\$\$@[a-zA-Z0-9_]+\b";
        var stringVariableMatches = Regex.Replace("$$@Unknown and $$@Key", pattern, 
                m => variablesDictionary.ContainsKey(m.Value) ? variablesDictionary[m.Value] : m.Value);
        Console.WriteLine(stringVariableMatches);
    }
}

Output: $$@Unknown and Value.

• Ctrl+H
• Find what: ^(\w+,\h*)(\w+)(?:,\h*(\w+))?(?:,\h*(\w+))?(?:,\h*(\w+))?(?:,\h*(\w+))?(?:,\h*(\w+))?(?:,\h*(\w+))?(?:,\h*(\w+))?(?:,\h*(\w+))?(?:,\h*(\w+))?
• Replace with: $1$2\n(?3$1$3)(?4\n$1$4)(?5\n$1$5)(?6\n$1$6)(?7\n$1$7)(?8\n$1$8)(?9\n$1$9)
• TICK Match case
• TICK Wrap around
• SELECT Regular expression
• UNTICK . matches newline
• Replace all

Explanation:

^               # beginning of line
    (               # group 1
        \w+             # 1 or more word characters
        ,               # a comma
        \h*             # 0 or more horizontal spaces
    )               # end group 1
    (\w+)           # group 2, 1 or more word characters
    (?:             # non capture group
        \h*             # 0 or more horizontal spaces
        (\w+)           # group 3, 1 or more word characters
    )?              # end group, optional
(?:,\h*(\w+))?      # same as above
(?:,\h*(\w+))?      # same as above
(?:,\h*(\w+))?      # same as above
(?:,\h*(\w+))?      # ... 
(?:,\h*(\w+))?      # ... 
(?:,\h*(\w+))?      # ... 
(?:,\h*(\w+))?      # ... 
(?:,\h*(\w+))?      # ... 

Replacement:

$1              # content of group 1
$2              # content of group 2
\n              # line feed, you can use \r\n for Windows
(?3             # if group 3 exists
    $1              # content of group 1
    $3              # content of group 3
)               # endif
(?4\n$1$4)      # same as above
(?5\n$1$5)      # ...
(?6\n$1$6)      # ...
(?7\n$1$7)      # ...
(?8\n$1$8)      # ...
(?9\n$1$9)      # ...

Screenshot (before):

Screenshot (after):

Just use a group reference in your replacement:

string = "hello i am [12@fname lname] and i am referring this user [23@fname1 lname1]"

newstr = string.replace(/\[(.+?)@(.+?)\]/g, '<some-tag id="$1"/>')

console.log(newstr)

You don't need a regex, you simply can use Replace:

string input = "this is a test AAA one more test adakljd jaklsdj BBB sakldjasdkj CCC";
string replaced = input.Replace("AAA", "XXX").Replace("BBB", "XXX")...