Shell Programming and Scripting

#! /usr/bin/tclsh

if { $argc != 1 } {
        puts stderr "Usage: $argv0 <input-file>"
        exit 1
}
set inputfile [lindex $argv 0]
if { [file exists $inputfile] == 0 } {
        puts stderr "Error. $inputfile does not exist"
        exit 2
}

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


set fp [open $inputfile r]
while { [gets $fp line] >= 0 } {
        foreach { a b c d } [split $line ,] {}
        puts "$a,$b,$c,[commify $d]"
}
close $fp

awk 'BEGIN{FS=","}
 function cfmt(n  , s) {
   s = (ThouSep ? ThouSep : ",") "&"  # US convention the default
   while ( n ~ /^ *[-+(]? *[0-9][0-9][0-9][0-9]/ )
     sub ( /[0-9][0-9][0-9]([^0-9].*|$)/, s, n )
   return n
 } 
{
  print cfmt($4)      
}
' file

$ echo 1234567890 | sed -e :a -e 's/^\([^.]*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta'
1,234,567,890
$ echo 12345678.90 | sed -e :a -e 's/^\([^.]*[0-9]\)\([0-9]\{3\}\)/\1,\2/;ta'
12,345,678.90