how to replace one line of a file with php - php

Question

I want to replace one line of a file with php, how can i do it?
This is the code where i print the line that I want to replace:
$file = fopen("file.dat", "a+");
$eqs = file_get_contents("file.dat");
$eqs = preg_split( "/\n/", $eqs );
foreach ($eqs as $valor) {
if(strpos($valor, $sn) !== false){
echo $valor; //this is the line to replace
} else{
echo "Not found";
}
}
Thanks in advance

Answer 1

As deceze♦ mentioned, unless the line is of fixed length, the easiest way is to process the whole file and output it to a new file.
Create a variable $newdata to append the processed data.
If your strpos statement !== false then you can change that text with the $replace_text variable and append that instead.
Once the loop has finished save your output to a new file. (If PHP has the appropriate permissions)
$file = fopen("file.dat", "a+");
$eqs = file_get_contents("file.dat");
$eqs = preg_split( "/\n/", $eqs );
$newdata = "";
foreach ($eqs as $valor) {
if(strpos($valor, $sn) !== false){
echo $valor; //this is the line to replace
$replace_text = "test";
$newdata = $newdata.$replace_text."/\n/";
} else{
$newdata = $newdata.$valor."/\n/";
}
}
$myfile = fopen("newfile.dat", "w") or die("Unable to open file!");
fwrite($myfile, $newdata);
fclose($myfile);

Answer 2

I would suggest this solution because it saves resources by processing line by line.
$source = fopen('file.dat', "r");
$target = fopen('file.dat.tmp', "w");
while ($line = fgets($source)) {
if(strpos($line, $sn) === false){
fputs($target, $line);
}
}
fclose($source);
fclose($target);
unlink('file.dat');
rename('file.dat.tmp','file.dat');