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 stackoverflow.com/questions/8163746/… contain any useful information? — Nigel Ren
– Nigel Ren, Commented May 28, 2020 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
– Scoots, Commented May 28, 2020 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
– Nico Haase, Commented May 28, 2020 at 15:59

AbraCadaver · Accepted Answer · 2020-05-28 21:55:49Z

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, 2020 at 21:55

answered May 28, 2020 at 15:45

AbraCadaver

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RiggsFolly · Accepted Answer · 2020-05-28 15:49:17Z

1

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

edited May 28, 2020 at 15:49

answered May 28, 2020 at 15:39

RiggsFolly

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1 Comment

RiggsFolly Over a year ago

@Scoots Added an alternative if that is an issue to the OP :)

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