1.testwrite.php

<?php                                                                                                                                                 

$fp = fopen('/home/thcipriani/test.txt', 'w');
fwrite($fp, 'hello');
fwrite($fp, ' ');
fwrite($fp, 'world');
fwrite($fp, "\n");

fclose($fp);

strace-hhvm.out

14371 open("/home/thcipriani/test.txt", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 8                                                                           
14371 lseek(8, 0, SEEK_CUR)             = 0                                                                                                           
14371 lseek(8, 0, SEEK_SET)             = 0                                                                                                           
14371 write(8, "hello", 5)              = 5                                                                                                           
14371 lseek(8, 0, SEEK_CUR)             = 5                                                                                                           
14371 lseek(8, 5, SEEK_SET)             = 5                                                                                                           
14371 write(8, " ", 1)                  = 1                                                                                                           
14371 lseek(8, 0, SEEK_CUR)             = 6                                                                                                           
14371 lseek(8, 6, SEEK_SET)             = 6                                                                                                           
14371 write(8, "world", 5)              = 5                                                                                                           
14371 lseek(8, 0, SEEK_CUR)             = 11                                                                                                          
14371 lseek(8, 11, SEEK_SET)            = 11                                                                                                          
14371 write(8, "\n", 1)                 = 1                                                                                                           
14371 close(8)                          = 0  

strace-php.out

14404 open("/home/thcipriani/test.txt", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4                                                                           
14404 fstat(4, {st_mode=S_IFREG|0664, st_size=0, ...}) = 0                                                                                            
14404 lseek(4, 0, SEEK_CUR)             = 0                                                                                                           
14404 write(4, "hello", 5)              = 5                                                                                                           
14404 write(4, " ", 1)                  = 1                                                                                                           
14404 write(4, "world", 5)              = 5                                                                                                           
14404 write(4, "\n", 1)                 = 1                                                                                                           
14404 close(4)                          = 0