如何检查txt文件中的重复内容？

I have a .txt file which contains objects on each line.Meaning the first line is "baby",second line "toddler",next line "dog" and the line after is "cat".

I want to be able to add objects into my txt file using php but i want to prevent duplicates.Somehow my codes only work for "dog".When i try to add "dog" it will say this object already exist but when i try "cat" / "baby" /"toddler" it still adds even though it is already in the list.

CODES

$check = false;
    if(isset($_POST['add'])){
        if($_POST['addLbl'] == ''){
            echo ' Please enter a label';
            $check = true;
        }
        else{
            $data = "
".$_POST['addLbl'];
            $file_lines = file('lbls/predefined_classes.txt');

            foreach($file_lines as $line){
                if($_POST['addLbl'] === $line){
                    $check = true;
                }
            }
            if($check === false){
                $ret = file_put_contents('lbls/predefined_classes.txt',$data,FILE_APPEND | LOCK_EX);
                    if($ret === false){
                        echo ' Unable to add.An error occurred.';
                    }
                    else{
                        echo ' Sucessfully added!';
                        $_POST['addLbl'] = '';
                    }
            }else{
                echo 'The label '.$_POST['addLbl'].' already exists.';
            }

        }

Txt File Content

because you add list manualy and have white space in the end of each line add trim() function solve problem

<?php

$check = false;
if(isset($_POST['add'])){

    if($_POST['addLbl'] == ''){
        echo ' Please enter a label';
        $check = true;
    }
    else{
        $data = "
".$_POST['addLbl'];
        $file_lines = file('lbls/predefined_classes.txt');
        foreach($file_lines as $line){
            if($_POST['addLbl'] === trim($line)){ // trim() added here
                $check = true;
            }
        }
        if($check === false){
            $ret = file_put_contents('lbls/predefined_classes.txt',$data,FILE_APPEND | LOCK_EX);
                if($ret === false){
                    echo ' Unable to add.An error occurred.';
                }
                else{
                    echo ' Sucessfully added!';
                    $_POST['addLbl'] = '';
                }
        }else{
            echo 'The label '.$_POST['addLbl'].' already exists.';
        }

    }
}
    ?>

output test for cat :

The label cat already exists.

try the following, little shorter with same logic. No need for $check among other improvements.

    if(isset($_POST['add'])){
        if($_POST['addLbl'] == ''){
            echo ' Please enter a label';
        }
        else{
            $data = "
".$_POST['addLbl'];
            $file_str = file_get_contents('lbls/predefined_classes.txt');

            if (!strrpos ( $file_str , $data)) { // not found
                $ret = file_put_contents('lbls/predefined_classes.txt',$data,FILE_APPEND | LOCK_EX);
                    if($ret === false){
                        echo ' Unable to add.An error occurred.';
                    }
                    else{
                        echo ' Sucessfully added!';
                        $_POST['addLbl'] = '';
                    }
            }else{
                echo 'The label '.$_POST['addLbl'].' already exists.';
            }
        }
    }

You get lines with the new line character. Read the file and split it into lines.

$newline = PHP_EOL;  // your editor might use another new line character
if(in_array($_POST['addLbl'], explode($newline, file_get_contents('test.txt'))))
  // echo error message
else
  // append to file

The entire task can be done in a few lines. Btw. check also for unset $_POST entries.

if(isset($_POST['add']))
{
  if(!isset($_POST['addLbl']) || $_POST['addLbl'] === '')
    echo ' Please enter a label';
  elseif(in_array($_POST['addLbl'], explode(PHP_EOL, file_get_contents('lbls/predefined_classes.txt'))))
    echo "The label {$_POST['addLbl']} already exists.";
  elseif(false === file_put_contents('lbls/predefined_classes.txt',PHP_EOL . $_POST['addLbl'], FILE_APPEND | LOCK_EX))
    echo ' Unable to add.An error occurred.';
  else
  {
    echo ' Sucessfully added!';
    $_POST['addLbl'] = '';
  }
}

The $file_lines array looks like as below
array
(
[0] => 

[1] => baby

[2] => toddler

[3] => cat

[4] => dog
)

You must remove next line escape sequence(i.e, ) from $line and then compare with $_POST['addLbl']