diff: text file permission denied

问题

I am on Windows and using diff to compare two text files. It was working successfully for small files but, when I start comparing 2GB file with another 2GB file it shows me:

diff: C:/inetpub/wwwroot/webclient/database_sequences/est_mouse_2.txt: Permission denied

My code:

$OldDatabaseFile = "est_mouse_1";
$NewDatabaseFile = "est_mouse_2";
shell_exec("C:\\cygwin64\\bin\\bash.exe --login -c 'diff $text_files_path/$OldDatabaseFile.txt $text_files_path/$NewDatabaseFile.txt >  $text_files_path/TempDiff_$OldDatabaseFile$NewDatabaseFile.txt 2>&1'");

est_mouse_1.txt and est_mouse_2.txt are created by me and I check file permission and folder permission, it is full control. And all other text files which I compared are in the same folder and they were successfully compared.

Any idea?

回答1:

You are using cygwin for this operation, Cygwin's heap is extensible. However, it does start out at a fixed size and attempts to extend it may run into memory which has been previously allocated by Windows. Heap memory can be allocated up to the size of the biggest available free block in the processes virtual memory (VM). On 64 bit systems this results in a 4GB VM for a process started from that executable. I think that why you can't compare two 2GB files, I agree that the error pretty strange but explains that your access to the memory is limited. Please see cygwin user guide for the more info.

来源：https://stackoverflow.com/questions/36516603/diff-text-file-permission-denied