trim lines and shrink whitespaces using regex for multi line string

Question

I\'m using a php function want to create a function to trim all unnecessary white spaces from a multi line string.

The regex that it\'s not working is the one tha

Answer 1

You may redefine where $ matches using the (*ANYCRLF) verb.

See the following PHP demo:

$s = " ffffd    \r\n  bbb     ";
$n = preg_replace('~(*ANYCRLF)\h+$~m', '', $s); // if the string can contain Unicode chars,
echo $n;                                        // also add "u" modifier ('~(*ANYCRLF)\h+$~um')

Details:

• (*ANYCRLF) - specifies a newline convention: (*CR), (*LF) or (*CRLF)
• \h+ - 1+ horizontal whitespace chars
• $ - end of line (now, before CR or LF)
• ~m - multiline mode on ($ matches at the end of a line).

If you want to allow $ to match at any Unicode line breaks, replace (*ANYCRLF) with (*ANY).

See Newline conventions in the PCRE reference:

(*CR)        carriage return
(*LF)        linefeed
(*CRLF)      carriage return, followed by linefeed
(*ANYCRLF)   any of the three above
(*ANY)       all Unicode newline sequences

Now, if you need to

• Trim the lines from both start and end
• Shrink whitespaces inside the lines into just a single space

use

$s = " Ł    ę  d    \r\n  Я      ёb     ";
$n = preg_replace('~(*ANYCRLF)^\h+|\h+$|(\h){2,}~um', '$1', $s);
echo $n;

See the PHP demo.