PHP Regular Expressions Reading Records with a Pattern Separator

PHP Regular Expressions

Reading Records with a Pattern Separator

Problem

You want to read in records from a file, in which each record is separated by a pattern you can match with a regular expression.

Solution

Read the entire file into a string and then split on the regular expression:

       $contents = file_get_contents('/path/to/your/file.txt');

       $records = preg_split('/[0-9]+\) /', $contents);

Discussion

This breaks apart a numbered list and places the individual list items into array elements. So if you have a list like this:

       1) Gödel

       2) Escher

       3) Bach

you end up with a four-element array, with an empty opening element. That’s because preg_split() assumes the delimiters are between items, but in this case, the numbers are before items:

       array(4) {

            [0]=>

            string(0) ""

            [1]=>

            string(7) "Gödel

       "

            [2]=>

            string(7) "Escher

       "

            [3]=>

            string(5) "Bach

       "

       }

From one point of view, this can be a feature, not a bug, because the nth element holds the nth item. But, to compact the array, you can eliminate the first element:

       $records = preg_split('/[0-9]+\) /', $contents);

       array_shift($records);

Another modification you might want is to strip newlines from the elements and substitute the empty string instead:

       $records = preg_split('/[0-9]+\) /', str_replace("\n",'',$contents));

       array_shift($records);

PHP doesn’t allow you to change the input record separator to anything other than a newline, so this technique is also useful for breaking apart records divided by strings. However, if you find yourself splitting on a string instead of a regular expression, substitute explode() for preg_split() for a more efficient operation.