In your prior post, lower processing time was the goal, not an artificial avoidance of loops not generated within the regex engine. See my reply Re: How do I match lines of 40 characters long in a block of text? for an efficient loop.

Accepting that this is homework or a bar bet; if you must use a regex to decide that a block of text has fewer than five short lines, try to match five or more - failure is success:

if ($foo !~ m/\A(?:             #anchor start and group
                 (?:.{41,}\n)*  #maybe some long lines 
                 (?:.{0,40}\n)  #one short line
               ){5,}            #five or more
               (?:.{41,}\n)*    #maybe some more long lines 
               \z               #anchor end
             /x ) {
    #do something
}
[download]

Update: Fixed link. Your first regex may work if you anchor the ends. It is matching long lines by backtracking to the -40 position from the newline.

After Compline,
Zaxo

My reply at Re: How do I match lines of 40 characters long in a block of text? does what you want I think. Note that you don't really want to match 0 lines unless you want everything to match. Also, when you are constructing a regex, it is best to be able to state exactly what you want. I think you really want "1 to 4 lines each consisting of 0 to 40 characters followed by a newline." I've included the code from original reply below for your convenience.

/
(               # Assuming you want capture these lines.
  (?:           # Group each line.
     ^          # Beginning of the line.
     .{0,40}\n  # 0 to 40 characters followed by a newline. 
  ){1,4}        # 1 to 4 lines. (0 will permit an empty match.)
)               # Done capturing.
/mx;            # /m so that ^ anchor works, /x for comments.
[download]

-sauoq
"My two cents aren't worth a dime.";

Thanks! However this is not working for me! Here is my code:

$foo = "line1line1line1line1line1line1line1line1
line2line2line2line2line2line2line2line2line2line2line2line2line2line2
+line2line2line2line2
line3line3line3line3line3line3line3line3";

if ($foo =~ /((?:^.{0,40})\n{1,4})/m)            
{ print "$1: OK\n\n"; } 


else
{print "$1: NOT OK\n\n";}
[download]


I get this as a result: line1line1line1line1line1line1line1line1
: OK

Which is not good, since line2 is greater than 40 chars.

thanks!

Well, that's exactly what it should match. Your input matches your requirements. It has a block of text consisting of between 1 and 4 (1 in this case) lines of not more than 40 characters and an additional newline.

Your requirements are poorly specified.

Maybe, rather than see if your input matches such a block, you want to see if your input is such a block. If this is the case, your example input wouldn't work even if the second line had less than forty characters because your third line doesn't have a trailing newline.

If that is what you are trying to do, try this:

/
^               # Anchor to beginning of string.
  (?:           # Group each line.
     .{0,40}\n  # 0 to 40 characters followed by a newline. 
  ){0,4}        # 0 to 4 lines.
$               # Anchor to end of string.
/x;             # /x for comments.
[download]

-sauoq
"My two cents aren't worth a dime.";

See Re: How do I match lines of 40 characters long in a block of text?.