Regular Expression - Matching and extracting complicated conditions - regex

Question

I'm trying to write a regular expression that will match these conditions:
Maximum of 8000 characters (any characters, including "\r\n")
Maximum of 10 lines (separated by \r\n).
to extract from the matched text only the first 4 lines.
Can't find a good way do it...:/
Thanks!!

Answer 1

Regular expressions are not what you need. They are used to match a certain pattern, not a certain length. If you are holding the data in a string, myString.length <= 8000 is all you need for the character count (using the correct syntax for your language, of course). For the number of lines, you will have to count the number of \r\n sequences in your string (can be done iteratively). To get the first four lines, just find the 4th \r\n and get everything before that with a substring method.

Answer 2

Description
This expression does the following:
validates the input string is between zero and 8,000 characters
validates there are at most 10 line of new line delimited text
then captures the first 4 new line delimited lines of text
\A(?=.{0,8000}\Z)(?=(?:^.*?(?:\r|\n|\Z)){0,10}\Z)(?:^.*?[\r\n\Z]+){0,4} This requires options: m multiline, and s dot matches all characters
Expanded
\A anchor to the begining of the string, this anchor allows the use of the s option which allows the . to match new line and line feed characters
(?=.{0,8000}\Z) look ahead and validate there are between zero and 8000 characters
(?=(?:^.*?(?:\r|\n|\Z)){0,10}\Z) look ahead and validate there are no more then 10 new line delimited lines
(?:^.*?[\r\n\Z]+){0,4} match the first 4 lines of text
PHP Code Example:
You didn't specify a language so I'm including this PHP example to show how it works and the sample output.
Input Text
This input test is 8 lines of new line delimited strings. There are only 1779 characters here.
Far far away, behind the word mountains, far from the countries Vokalia and Consonantia, there live the blind texts. Separated they live in Bookmarksgrove right at the coast of the Semantics, a large language ocean. A small
river named Duden flows by their place and supplies it with the necessary regelialia. It is a paradisematic country, in which roasted parts of sentences fly into your mouth. Even the all-powerful Pointing has no control about
the blind texts it is an almost unorthographic life One day however a small line of blind text by the name of Lorem Ipsum decided to leave for the far World of Grammar. The Big Oxmox advised her not to do so, because there were
thousands of bad Commas, wild Question Marks and devious Semikoli, but the Little Blind Text didn’t listen. She packed her seven versalia, put her initial into the belt and made herself on the way. When she reached the first hills of
the Italic Mountains, she had a last view back on the skyline of her hometown Bookmarksgrove, the headline of Alphabet Village and the subline of her own road, the Line Lane. Pityful a rethoric question ran over her cheek, then
she continued her way. On her way she met a copy. The copy warned the Little Blind Text, that where it came from it would have been rewritten a thousand times and everything that was left from its origin would be the word "and"
and the Little Blind Text should turn around and return to its own, safe country. But nothing the copy said could convince her and so it didn’t take long until a few insidious Copy Writers ambushed her, made her drunk with Longe
and Parole and dragged her into their agency, where they abused her for their projects again and again. And if she hasn’t been rewritten, then they are still using her.
Code
<?php
$sourcestring="your source string";
preg_match('/\A(?=.{0,8000}\Z)(?=(?:^.*?(?:\r|\n|\Z)){0,10}\Z)(?:^.*?[\r|\n\Z]+){0,4}/ims',$sourcestring,$matches);
echo "<pre>".print_r($matches,true);
?>
Matches
$matches Array:
(
[0] => Far far away, behind the word mountains, far from the countries Vokalia and Consonantia, there live the blind texts. Separated they live in Bookmarksgrove right at the coast of the Semantics, a large language ocean. A small
river named Duden flows by their place and supplies it with the necessary regelialia. It is a paradisematic country, in which roasted parts of sentences fly into your mouth. Even the all-powerful Pointing has no control about
the blind texts it is an almost unorthographic life One day however a small line of blind text by the name of Lorem Ipsum decided to leave for the far World of Grammar. The Big Oxmox advised her not to do so, because there were
thousands of bad Commas, wild Question Marks and devious Semikoli, but the Little Blind Text didn’t listen. She packed her seven versalia, put her initial into the belt and made herself on the way. When she reached the first hills of
)