在文本文件行的中心长度位置添加换行符

input.txt

just some example text, just some example text
some example text
example text, just some example text

$inFile  = "input.txt";    
$outFile = "output.txt";


$data = array();

$ftm = fopen($outFile, "w+");
$fh = fopen($inFile, "r");      

$data = file($inFile);
foreach ($data as $key => $value)
{
    $row = $value;
    $str_length = strlen($row);

    if ($str_length > 10)
    {
        $width = strlen($row)/2;
        $wrapped = wordwrap($row, $width);

        fwrite($ftm, $wrapped);
    }
    else
    {
        fwrite($ftm, $row);
    }
}
fclose($fh);

How can I add a newline to the center position of each line?

//Related:
$wrapped = wordwrap($row, $width, '\N');

I'm not sure if this is what you're expecting, but it works given supplied text:

just some example text
some example text
example text

which results to a written file as: (if using ' ')

just some
example
text
some
example
text
example
text

(EDIT) and as:

just some
example
text
some
example
text
example
text

(if using " ") which will result having no spaces at the end of each line.

PHP

<?php
$inFile  = "input.txt";    
$outFile = "output.txt";

$data = array();

$ftm = fopen($outFile, "w+");
$fh = fopen($inFile, "r");      

$data = file($inFile);
foreach ($data as $key => $value)
{

$newline = "
"; // writes to file with no spaces at the end of each line
// $newline = '
'; // use single quotes if wanting to write 
 in the file

    $row = $value;
    $str_length = strlen($row);

    if ($str_length > 10)
    {

        $width = strlen($row) / 2;
        $wrapped = wordwrap($row, $width, $newline);

        fwrite($ftm, $wrapped);
    }
    else
    {
        fwrite($ftm, $row);

    }
}
fclose($fh);