PHP String replace on certain lines only

Question

I currently have a file such as this.

[Line 1] Hello
[Line 2] World
[Line 3] Hello World

I wish to look for all lines containing "Hello" which would be Line 1 and 3.

Then I would like to change on that line all cases of "Line" to "Changed" so the output would be

[Changed 1] Hello
[Line 2] World
[Changed 3] Hello World

With line two being untouched. I currently have code to locate all lines with Hello in them, but am unsure how to edit those lines alone and no other.

For example the code below does find all the lines, but also deletes everything in the process with the str_replace, so I know it's not str_replace I'm seeking.

$lines = file("lines.html");
$find = "Hello";
$repl = "Changed";
foreach($lines as $key => $line)
  if(stristr($line, $find)){$line = str_replace("$find","$repl",$line);}

Does https://stackoverflow.com/questions/8163746/how-do-i-replace-certain-parts-of-my-string contain any useful information? — Nigel Ren, May 28 '20 at 15:33
What about cases where the string contains "Hello" but doesn't lead with it? e.g. `[Line 4] He Said Hello` — Scoots, May 28 '20 at 15:38
What do you mean by "the troubled area"? What have you tried so far? If you have identified which lines to change, why not run a simple string replacement on these lines? — Nico Haase, May 28 '20 at 15:59
Sorry about the delay. I picked an answer and will make my current question more clear to show one of the things I tried. — AtomicSteed, Jun 07 '20 at 18:57

RiggsFolly · Answer 1 · 2020-05-28T15:49:17.410

To change anything, you will have to write a new file with the existing lines and the newly changed lines. Here is a simple example

// create a new output file
$out = fopen('test2.txt', 'w');

$input = file("lines.html");
$find = "Hello";
foreach($input as $key => $line){
    $tmp = $line;
    if(stristr($line, $find)){
        $tmp = str_replace('[Line', '[Changed', $line);
        // or if `[Line` can appear more than once in the line
        //$tmp = substr_replace($line, '[Changed', 0, 5);
    }
    fwrite($out, $tmp);
}
fclose($out);

RESULT

[Changed 1] Hello
[Line 2] World
[Changed 3] Hello World

@Scoots Added an alternative if that is an issue to the OP :) — RiggsFolly, May 28 '20 at 15:50

AbraCadaver · Accepted Answer · 2020-05-28T21:55:49.310

1

Here's a quick way if $find = "Hello"; and $repl = "Changed";:

$result = preg_replace("/\[Line (\d+\].*?$find.*)/", "[$repl $1", file("lines.html"));
file_put_contents("lines.html", $result);

Match [Line and capture () digits \d one or more +
Followed by anything .*? then the $find string then anything .* capturing all
Replace with [ $repl and what was captured $1

edited May 28 '20 at 21:55

answered May 28 '20 at 15:45

AbraCadaver

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PHP String replace on certain lines only

2 Answers2