Iterate over each line in a string

04/10/2020 09:00:01

I have a form that allows the user to either upload a text file or copy/paste the contents of the file into a textarea. I can easily differentiate between the two and put whichever one they entered into a string variable, but where do I go from there?

I need to iterate over each line of the string (preferably not worrying about newlines on different machines), make sure that it has exactly one token (no spaces, tabs, commas, etc.), sanitize the data, then generate an SQL query based off of all of the lines.

I'm a fairly good programmer, so I know the general idea about how to do it, but it's been so long since I worked with PHP that I feel I am searching for the wrong things and thus coming up with useless information. The key problem I'm having is that I want to read the contents of the string line-by-line. If it were a file, it would be easy.

I'm mostly looking for useful PHP functions, not an algorithm for how to do it. Any suggestions?

Verified Answer (184 Votes)

09/23/2009 03:33:49

preg_split the variable containing the text, and iterate over the returned array:

foreach(preg_split("/((\r?\n)|(\r\n?))/", $subject) as $line){
    // do stuff with $line

Answer #2 (147 Votes)

02/09/2013 19:32:29

I would like to propose a significantly faster (and memory efficient) alternative: strtok rather than preg_split.

$separator = "\r\n";
$line = strtok($subject, $separator);

while ($line !== false) {
    # do something with $line
    $line = strtok( $separator );

Testing the performance, I iterated 100 times over a test file with 17 thousand lines: preg_split took 27.7 seconds, whereas strtok took 1.4 seconds.

Note that though the $separator is defined as "\r\n", strtok will separate on either character - and as of PHP4.1.0, skip empty lines/tokens.

See the strtok manual entry:


Answer #3 (94 Votes)

12/25/2012 15:55:45

If you need to handle newlines in diferent systems you can simply use the PHP predefined constant PHP_EOL ( and simply use explode to avoid the overhead of the regular expression engine.

$lines = explode(PHP_EOL, $subject);
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