Title: Add Commas to a Number
Submitter: Keith Vetter (other recipes)
Last Updated: 2001/09/09
Version no: 1.0
Category: Text Processing

Description:

Takes a number and inserts a comma (or separator of your choice) between
every third digit.

Source: Text Source

proc comma {num {sep ,}} {
    while {[regsub {^([-+]?\d+)(\d\d\d)} $num "\\1$sep\\2" num]} {}
    return $num
}

The license for this recipe is available here.

Discussion:

Numbers displayed with the appropriate commas are much easier for a
person to read. This code is based on an example from the Perl documentation.