Excel Regex to find and replace strings using regular expressions

RegExpReplace syntax

The RegExpReplace function searches an input string for values that match a regular expression and replaces the found matches with the text you specify.

The function accepts 5 arguments, but only the first three are required.

Where:

• Text (required) - the text string to search in.
• Pattern (required) - the regular expression to match.
• Text_replace (required) - the text to replace the matching substrings with.
• Instance_num (optional) - a serial number indicating which instance to replace. If omitted, the function will replace all found matches (default).
• Match_case (optional) - controls whether to match or ignore text case. If TRUE or omitted (default), the search is case-sensitive; if FALSE - case-insensitive.

The function works in all versions of Excel 365, Excel 2021, Excel 2019, Excel 2016, Excel 2013 and Excel 2010.

Usage notes

To ensure that your results will meet your expectations, let's take a closer look at the inner mechanics:

1. By default, the function works in the Replace all mode. To substitute a specific occurrence, put a corresponding number in the instance_num argument.
2. By default, the function is case-sensitive. For case-insensitive search, set the match_case argument to FALSE. Because of the VBA RegExp limitations, the classic case-insensitive pattern (?i) is not supported.
3. When you supply a regex directly in a formula, remember to enclose it in double quotation marks.
4. If a valid pattern is not found, the function will return the original string with no changes.
5. If the regex is invalid, a #VALUE! error will occur.

Regex to replace string matching a pattern

In the sample dataset below, supposing you want to hide some personal data such as social security numbers. Given that SSN is a nine-digit number in the format "000-00-0000", we are using the following regular expression to find it.

Pattern: \d{3}-\d{2}-\d{4}

For replacement, this string is used:

Replacement text: XXX-XX-XXXX

With the original string in A5, the complete formula takes this form:

=RegExpReplace(A5, "\d{3}-\d{2}-\d{4}", "XXX-XX-XXXX")

For convenience, you can enter the pattern and replacement text in separate cells and refer to those cells in your formula. If you plan to use the formula for multiple cells, remember to lock the cell addresses with the $ sign:

=RegExpReplace(A5, $A$2, $B$2)

Regex to replace number in a string

To find any single digit from 0 to 9, use \d in your regular expression. To find specific digits, use an appropriate quantifier or construct a more sophisticated regex like shown in the below examples.

Regex to find and replace all matches

In classic regular expressions, there is the global search flag /g that forces a regex to find all possible matches in a string. In VBA, this flag is not supported. Instead, the VBA RegExp object provides the Global property that defines whether to search for all occurrences or only the first one. In the code of our function, the Global property is set to True, meaning the pattern should be tested against all possible matches in a string.

So, what do you do to replace all occurrences matching a pattern? Nothing special. This behavior is implemented by default.

Let's say you manage an Excel file with personal data. Some information is confidential, so before sharing this file with your colleagues, you want to replace sensitive info such as social security numbers (SSN) and individual taxpayer identification numbers (ITIN) with "CONF".

Given that both SSN and ITIN have the same format, you can find them using the below regular expression.

Pattern: \d{3}-\d{2}-\d{4}

Since the 4^th instance_num argument of our function defaults to TRUE, you can safely omit it:

=RegExpReplace(A5, "\d{3}-\d{2}-\d{4}", "CONF")

As the result, all substrings matching the regex are replaced with the specified text:

Regex to replace a specific instance

To replace just one occurrence matching a given pattern, define the corresponding number in the instance_num argument.

In the above example, supposing you wish to replace only social security numbers. In all cells, SSN is listed first, so we are replacing the 1^st instance:

=RegExpReplace(A5, $A$2, $B$2, 1)

Where $A$2 is the pattern and $B$2 is the replacement text.

How to replace strings using regular expressions

Let's say you aim to replace text in square brackets with some character or string. The task can be accomplished with either a capturing group or positive look-arounds. The former is an easier way, so we'll stick to it.

Generally, to find a character that is "special" in regular expressions, you need to put a backslash right before it. In regexes, \ acts as an escape character that cancels the special meaning of the following character and turns it into a literal character. So, to find a bracket, you prefix it with a backslash: \[ to match an opening bracket and \] to match a closing bracket. Between the brackets, place a (capturing group). Depending on which quantifier you use in the group, different replacements will be made.

Greedy pattern: \[(.*)\]

This pattern performs a greedy search - consumes as much as possible. The .* expression matches as many characters as possible, and then tries to match ]. So, this pattern captures everything from the first opening bracket to the last closing bracket.

Lazy pattern: \[(.*?)\]

This pattern performs a lazy search - consumes as little as possible. The question mark ? forces .* to match as few characters as possible until it finds the next match in the pattern, which is ]. So, this pattern captures everything from the first opening bracket to the first closing bracket.

Negated class: \[([^\]]*)\]

One more way to match a substring in square brackets is to use a negation operator (^) inside the capturing group. From the first opening bracket, this pattern captures any characters other than a closing bracket, until it finds the first closing bracket. The result will be the same as with the lazy search.

Once you've decided on the regex, go "feed" it to the Ablebits Regex Replace function. Here's how:

1. On the Ablebits Data tab, in the Text group, click Regex Tools.
   

2. On the Regex Tools pane, configure these settings:
   • Select the source strings.
   • Enter your pattern.
   • Choose the Replace with option and type the replacement text in the box.
   • To have the results as formulas, not values, select the Insert as a formula check box.
   • Click the Replace button.

   

At a moment's notice, the AblebitsRegexReplace function is inserted in a new column to the right of your original data.

=AblebitsRegexReplace(A2, "\[(.*)\]", "*")

The pattern and replacement text you specify go to the 2^nd and 3^rd arguments, respectively. Alternatively, you can keep them in separate cells, and supply the corresponding cell references. In our case, we enter the patterns in cells B2 and C2, type the replacement value in A2, then compare the results and choose the desired outcome: