从字符串的开头或结尾删除非标准字符

Question

I am trying to manipulate some sentences, and I can remove the non standard characters from a string, but is there any way to do this only if it is at the beginning or end of a string? To remove non standard characters I am using the following:

 preg_replace("/[^A-Za-z0-9 ]/", '', $string);

I would like to change a string like this:

"* This is a sentence. --"

To be this:

"This is a sentence."

Answer 1

This isn't 100% robust, but this works:

preg_replace("/(?:^[^A-z0-9]+|[^.A-z0-9]+$)/", "", $input_lines);

Demo

Basically, it's replacing either anything at the beginning for the line that isn't Az, 0-9 with '' (since there are no matching groups) or ( | ) at the end anything after a full stop that isn't 0-9, Az.