Question

How can i get a particular line in a 3 gig text file. The lines are delimited by \n. And i need to be able to get any line on demand.

How can this be done? Only one line need be returned. And i would not like to use any system calls.

Note: There is the same question elsewhere regarding how to do this in bash. I would like to compare it with the PHP equiv.

Update: Each line is the same length the whole way thru.

Answer 1

Without keeping some sort of index to the file, you would need to read all of it until you’ve encountered x number of \n characters. I see that nickf has just posted some way of doing that, so I won’t repeat it.

To do this repeatedly in an efficient manner, you will need to build an index. Store some known file positions for certain (or all) line numbers once, which you can then use to seek to the right location using fseek.

Edit: if each line is the same length, you do not need the index.

$myfile = fopen($fileName, "r");
fseek($myfile, $lineLength * $lineNumber);
$line = fgets($myfile);
fclose($myfile);

Line number is 0 based in this example, so you may need to subtract one first. The line length includes the \n character.