japhy, am I missing something about why reverse regexen would be little known? The reverse commify thingie has been in perlfaq5 for about 4 years now.

But the algorithm was never named, nor paid much attention to. That FAQ entry is an isolated use of its powerful abilities.

japhy -- Perl and Regex Hacker

Am i missing something here?

This coma part of this script is exactly the one given in the FAQ BUT it adds two lines that make sure not to break tabular format --- which is all I wanted to share here.

fun.

Get Strong Together!!

I'm not sure that i follow, but if you have suggestions for improvements they are welcome.

One drawback is that when I use it for "ls -l" output as suggested, the year is commified as well as the file size. (For my older files, obviously). This then tends to mess up the column alignment, which the author had intended to preserve.

total 6,592
drwxr-xr-x   2 kromk    apbr         118,784 Jun 29  1,998 DSC/
-rwxr-xr-x   1 kromk    apbr           7,597 Oct 31 16:25 KEAVT.KTC*
drwxr-xr-x   7 kromk    apbr           4,096 Oct 17  1,999 archive/
drwxr-xr-x   6 kromk    apbr           4,096 Aug  7  2,000 backup/
drwxr-xr-x  46 kromk    apbr           8,192 Mar  7 14:03 build/
drwxr-xr-x   9 kromk    apbr          16,384 Mar  8 17:28 download/
[download]

Goes to show that you can't have everything...

buckaduck

This regex from Benjamin Goldberg will add commas to numbers:

s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g;
[download]

It is easier to see with comments:

s/(
   ^[-+]?            # beginning of number.
   \d+?              # first digits before first comma
   (?=               # followed by, (but not included in the match) :
      (?>(?:\d{3})+) # some positive multiple of three digits.
      (?!\d)         # an *exact* multiple, not x * 3 + 1 or whatever.
   )
   |                 # or:
   \G\d{3}           # after the last group, get three digits
   (?=\d)            # but they have to have more digits after them.
)/$1,/xg;
[download]