Replace character of a particular line with incremental number per line [duplicate] - php

Question

This question already has answers here:
Replace substrings with an incremented counter value
(5 answers)
Closed 2 years ago.
I have a text file (data.txt) with the following lines
# one
# two
a-two
b-two
c-two
# three
a-three
b-three
# four
I would like to replace # with incremental number per line so to be like this
1 one
2 two
a-two
b-two
c-two
3 three
a-three
b-three
4 four
I have try to do this
<?php
$path_to_file = 'data.txt';
$what_to_replace = '#';
$i = 0; // initial count
$file_contents = file_get_contents($path_to_file);
$file_contents = str_replace($what_to_replace, $i++,$file_contents);
file_put_contents($path_to_file,$file_contents);
?>
it did changed in all lines with # but not incrementally

Answer 1

Here's a simple way via preg_replace_callback():
$i = 1;
$file_contents = preg_replace_callback('/^#/m', function($match) use (&$i) {
return $i++;
}, $file_contents);
The m (multiline) flag is important - it will force our pattern to match # at the start of any line, not just the first.

Answer 2

I think you have to iterate over all the lines and replace the hash one by one. Of course, you can use some preg_replace as well to only replace the # at the line beginning: https://www.php.net/manual/en/function.preg-replace.php
$result = '';
$handle = fopen("data.txt", "r");
$i = 1;
if ($handle) {
while (($line = fgets($handle)) !== false) {
$content .= str_replace('#', $i++,$line) . "\n";
}
fclose($handle);
} else {
// error opening the file.
}
file_put_contents('data.txt', $result);

Answer 3

$path_to_file = 'data.txt';
$what_to_replace = '#';
$i = 1; // initial count
$file_contents = file_get_contents($path_to_file);
$lines = explode(PHP_EOL, $file_contents);
$new_lines = [];
foreach ($lines as $line) {
if (strpos($line, '#') !== false) {
$new_lines[] = str_replace('#', $i, $line);
$i++;
} else {
$new_lines[] = $line;
}
}
file_put_contents($path_to_file, implode(PHP_EOL, $new_lines));

Answer 4

We can split the text line-by-line, then process each line individually, looking for a # at the start of the line & modifying the output in those cases.
The preg_replace_callback approach is better than this one, IMO.
$text = file_get_contents(...);
$lines = explode("\n", $text); // split by unix-style line break
$out = []; // For storing the modified lines
$i=0;
foreach ($lines as $line){
if (substr($line,0,1)=='#'){
//replace the first character & increment the counter if line starts with #
$i++;
$line = $i.substr($line,1);
}
//append the SOMETIMES modified line to the output
$out[] = $line;
}
// convert array of lines to string
$fixedText = implode("\n", $out);
See https://stackoverflow.com/a/28725803/802469 for a more robust version of the explode("\n", $text) line.
Personally, I like the $out = []; ...; implode(...) approach. I find it easier to work with & to visualize in my mind. Using an $out = ""; $out .= $line."\n"; approach would work just as well. I suspect any performance increase from going with string would be negligible, but might lower your carbon footprint a small amount.
If you have serious performance/resource concerns (extremely large files) then the fopen()/while fgets() approach would be better, and fopen/fwrite() could be used to append each output line to a file without using up memory for an output string.