PHP Warning:  fopen(a.txt): failed to open stream:
No such file or directory in /root/test1.php on line 3

fopen(ファイル名,モード);

#!/usr/bin/php
<?php
$fl = fopen("a.txt","r");
$ln = fgets($fl);
fclose($fl);
print $ln."¥n";
?>

str_replace(array("¥r¥n","¥r","¥n"), "", $buffer);

<?php
  $fp = @fopen('sampledata.dat', 'r');

  if ($fp){
    $i = 1;
    while (!feof($fp)) {
      $buffer = fgets($fp);
      if($i == 3){
        if(strcmp(str_replace(array("¥r¥n","¥r","¥n"), "", $buffer),"<DDD>") == 0){
          print(str_ireplace('>','&gt;',str_ireplace('<','&lt;',$buffer)) . '
');
        }else{
          print(<br />');
        }
      }else{
        print($buffer . '<br />');
      }
      $i++;
    }
  }
  fclose($fp);
?>

aaa
bbb
<DDD>
ccc
ddd
eee
fff
ggg
hhh
iii
jjj
kkk
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