如何从字符串中修剪所有空格，但如果存在则保留单个尾随换行符

Question

我正在尝试创建一个简单的 php 函数，使其行为与 php trim() 函数相同，除了它保留一个尾随换行符（如果存在）。此外，它还需要支持保留CRLF、CR和LF的情况。

考虑以下用例：

1. myTrim(" \t \r\n 敏捷棕狐跳过懒狗\t \t ") === "敏捷棕狐跳过懒狗"
2. myTrim(" \t \r\n 敏捷棕狐跳过懒狗 \t \r\n\r\n \t \r\n ") === "敏捷棕狐跳过懒狗\r\n"
3. myTrim(" \t \r\n 敏捷棕狐跳过懒狗\t \r\r \t \r ") === "敏捷棕狐跳过懒狗\r"
4. myTrim(" \t \r\n 敏捷棕狐跳过懒狗\t \n\n \t \n ") === "敏捷棕狐跳过懒狗\n"

我没有成功尝试过如下功能：

public static function trimMessageBlock( $block )
{
    // Remove all leading whitespace (e.g. HT (9), LF (10), FF (12), CR (13), and space (32))
    $block = preg_replace("/^\s+/", "", $block);
    // Remove all trailing whitespace, but preserve a single trailing line break if one exists
    $block = preg_replace("/\s*(\R?)\s*$/", "$1", $block);

    return $block;
}

上面的代码似乎完全忽略了换行符，只匹配简单的大小写（\s*）。我能看到的唯一另一种方法是首先使用“if”语句来测试/\s*\R\s*$/ 模式，然后使用/\s*\R\s*$/ 或/\s+$/，具体取决于是否存在换行符。关于在正则表达式中执行此操作的更简单、更优雅的方法有什么建议吗？

顺便说一句，这是我在 stackoverflow 上的第一篇文章

Answer 1

你可以这样做。 （见 cmets）

<?php

function myTrim($str) {
    //Look for a non whitespace character with whitespace following.
    //Capture the first (either 1 or 2) consecutive line ending characters
    if (preg_match("/[^\s]\s*?(\R)\s*$/", $str, $capture)) {
        // return the trimmed string, plus the line break
        return trim($str) . $capture[1];
    }
    //No line endings were found
    return trim($str);
}

var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \t ") === "The quick brown fox jumps over the lazy dog");
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \r\n\r\n \t \r\n ") === "The quick brown fox jumps over the lazy dog\r\n");
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \r\r \t \r ") === "The quick brown fox jumps over the lazy dog\r");
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \n\n \t \n ") === "The quick brown fox jumps over the lazy dog\n");
//Added a couple more edge test cases
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \n\r\n \t \n ") === "The quick brown fox jumps over the lazy dog\n");
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \r\n\n \t \n ") === "The quick brown fox jumps over the lazy dog\r\n");

//Outputs
//bool(true) bool(true) bool(true) bool(true) bool(true) bool(true)     

Answer 2

简化...

function myTrim($str) {
    // if trailing line break exists, preserve it
    if ( preg_match("/\s*?(\R)\s*$/", $str, $capture) ) {
        // return the trimmed string, plus the line break
        return trim($str) . $capture[1];
    }

    // No line break was found, return the trimmed string
    return trim($str);
}

var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \t ") === "The quick brown fox jumps over the lazy dog");
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \r\n\r\n \t \r\n ") === "The quick brown fox jumps over the lazy dog\r\n");
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \r\r \t \r ") === "The quick brown fox jumps over the lazy dog\r");
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \n\n \t \n ") === "The quick brown fox jumps over the lazy dog\n");
//Added a couple more edge test cases
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \n\r\n \t \n ") === "The quick brown fox jumps over the lazy dog\n");
var_dump(myTrim(" \t \r\n The quick brown fox jumps over the lazy dog \t \r\n\n \t \n ") === "The quick brown fox jumps over the lazy dog\r\n");