$re = '/~\/remove\/me[^\s]*\/(?=[^\s]+)/mi';
$str = '~/remove/me/myexec.pl /some/other/path/exec.pl
/yet/another/path/pipeit.pl | ~/remove/me/subdir/tome.pl
~/remove/me/deeply/nested/exec.pl';
$subst = " ";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php