Re: Regex to match 20 chars of some digits followed by some spaces

[ysth]

/\d(?!.{0,18} \d)[\d ]{19}/

Matches 20 digits and spaces, beginning with a digit, where there are no digits following spaces.

Update: had 0,19, meant 19

[Roy Johnson]

Excellent. Piqued my interest in this approach, which led to a few observations:
• you probably want to anchor your match
• you could have used dot-star instead of .{0,18}, or you could have specified the chars for the dot (TIMTOWTDI) -- probably the most efficient thing would be to specify (?!\d* +\d), which made me realize...
• it can be done with a positive lookahead like so: /^\d(?=\d* *$)[\d ]{19}$/ ("leading digit, followed by digits, then spaces, then end of string, etc.")

[ysth]

I actually have never used Parse::RecDescent but was assuming it was working on an input buffer using the supplied regex as something like /\G$regex/gc so I didn't supply a beginning anchor and an ending anchor is not usable. I haven't got around to checking my assumption yet...and you know what they say when you assUme.

[ysth]

Well, I've read through Parse::RecDescent and it does work as I had guessed. So solutions to this problem should not have ^ and may not depend on $.